- Email: [email protected]
Latent Toxoplasma gondii infection leads to deficits in goal-directed behavior in healthy elderly
Neurobiology of Aging 35 (2014) 1037e1044
Contents lists available at ScienceDirect
Neurobiology of Aging journal homepage: www.elsevier.com/locate/neuaging
Latent Toxoplasma gondii infection leads to deficits in goal-directed behavior in healthy elderly Christian Beste a,1, Stephan Getzmann b, *,1, Patrick D. Gajewski b, Klaus Golka b, Michael Falkenstein b a b
Cognitive Neurophysiology, Department of Child and Adolescent Psychiatry, University of Dresden, Dresden, Germany Leibniz Research Centre for Working Environment and Human Factors at the Technical University of Dortmund (IfADo), Dortmund, Germany
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 August 2013 Received in revised form 11 November 2013 Accepted 13 November 2013 Available online 20 November 2013
Goal-directed behavior is well-known to show declines in elderly individuals, possibly because of alterations in dopaminergic neural transmission. The dopaminergic system is modulated by a number of other different factors. One of these factors, which has attracted a considerable amount of interest in neurobiology, but has only rarely been examined with respect to its possible modulatory role for cognitive functions in elderly individuals, is latent Toxoplasma gondii (T. gondii) infection. Latent T. gondii infection may be of relevance to goal-directed behavior as it alters dopaminergic neural transmission. We examine goal-directed behavior in T. gondii IgG positive and negative elderly subjects in auditory distraction paradigm. We apply event-related potentials to examine which cognitive subprocesses are affected by latent T. gondii infection on a neurophysiological level. We show that latent T. gondii infection compromises the management of auditory distraction in elderly by specifically delaying processes of attentional allocation and disengagement. The results show that latent T. gondii infection is neglected but an important neurobiological modulator of cognitive functions in elderly individuals. Ó 2014 Elsevier Inc. All rights reserved.
Keywords: Elderly individuals Aging Dopamine Cognitive flexibility Event-related potentials Toxoplasma gondii
1. Introduction Goal-directed behavior is orchestrated by a plenty of cognitive subprocesses and neurobiological systems. Very recent results provide conclusive evidence that the cortico-striatal system plays a pivotal role for goal-directed behavior based on auditory stimuli (Znamenskiy and Zador, 2013). Possibly this is the case because the striatum contains auditory sensory neurons (Nagy et al., 2005) likely involved in sound discrimination (Kropotov et al., 2000; Saft et al., 2008) and attentional control (Beste et al., 2008, 2009, 2011, 2012). These cortico-striatal circuits have frequently been shown to undergo degenerative changes in aging (e.g., Buckner, 2004), which likely underlies the susceptibility in elderly individuals to distracting stimuli from different sensory modalities leading to declines in goal-directed behavior (Getzmann et al., 2013a; Horvath et al., 2009; Ruzzoli et al., 2012). Besides changes in structural neuroanatomy, also changes in catecholaminergic neural * Corresponding author at: Leibniz Research Centre for Working Environment and Human Factors, Ardeystraße 67, D-44139 Dortmund, Germany. Tel.: þ49 231 1084 338; fax: þ49 231 1084 401. E-mail address: [email protected] (S. Getzmann). 1 Both authors contributed equally to this work and should be considered co-first authors. 0197-4580/$ e see front matter Ó 2014 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.neurobiolaging.2013.11.012
transmission occur in aging (for review: Bäckman et al., 2010). These changes in dopaminergic neural transmission contribute to deficits in goal-directed behavior in elderly individuals (e.g., Bäckman et al., 2010; Willemssen et al., 2011). However, the dopaminergic system is modulated by a number of different factors. One of these factors, which has attracted a considerable amount of interest in neurobiology, but has not been examined with respect to its possible modulatory role for cognitive functions in elderly individuals, is latent Toxoplasma gondii (T. gondii) infection. T. gondii is one of the most successful protozoan parasites on earth with an estimated prevalence of 30% in the world (Flegr, 2013; Tenter et al., 2000; Webster, 2007). T. gondii contains genes coding for tyrosine hydroxylase (Gaskell et al., 2009) needed to transform tyrosine into L-Dopa (e.g., Fillenz, 1993) in humans. T. gondii has thus been shown to increase the release of dopamine several-fold even after acute infection (McConkey et al., 2013; Prandovszky et al., 2011). Corroborating the role of T. gondii in dopaminergic neural transmission, it has been shown that T. gondii is related to the incidence of schizophrenia (e.g., Webster et al., 2007, 2013) and possibly Parkinson’s disease (Miman et al., 2010). Further evidence shows that haloperidol, a D2-receptor antagonist, is able to alleviate symptoms of acute T. gondii infection (Webster et al., 2006). Studies in healthy young humans suggest that even latent T. gondii infection leads to decreased performance in several
1038
C. Beste et al. / Neurobiology of Aging 35 (2014) 1037e1044
cognitive functions (Flegr, 2007, 2013). Similar results are also obtained in animal studies (e.g., Flegr, 2013; Gatkowska et al., 2012). It is therefore plausible that latent T. gondii infection leads to declines in goal-directed behavior in healthy elderly individuals. Because of the high prevalence, T. gondii infection status may be an important variable contributing to the high inter-individual differences in cognitive functions in elderly individuals. In the present study we use an auditory distraction paradigm and record event-related potentials (ERPs) to examine which cognitive subprocesses involved in goal-directed behavior are modulated by latent T. gondii infection in elderly individuals. In this paradigm a sequence of repeating short and long tones is presented, and distraction is induced by presenting stimuli at a pitch different from the usual tones. Subjects have to attend to a task-relevant tone feature (i.e., tone duration), while ignoring the deviant tone feature (i.e., tone pitch; e.g., Schröger and Wolf, 1998; Schröger et al., 2000). Processes related to stimulus detection are reflected in the P1 and N1 ERPs (e.g., Herrmann and Knight, 2001). The deviance in tone pitch is detected in sensory memory and reflected by the mismatch negativity (MMN) (for review: Näätänen et al., 2012). Subsequent mechanisms of attentional shifting toward the distractor and an adjustment of mental resources are reflected in the P3a (Escera et al., 2000; Getzmann et al., 2013b; Polich, 2007). Processes related to the recovery from distraction are reflected in the reorienting negativity (RON) (e.g., Schröger et al., 2000). T. gondii may in principle affect all of these subprocesses. However, mechanisms related to bottom-up stimulus detection (P1 and N1), and especially sensory memory processes (MMN) have been shown to strongly depend on glutamatergic neural transmission (Beste et al., 2008; Javitt et al., 1996; Turchi and Sarter, 2001; Umbricht et al., 2002). On the contrary, working memory and central executive processes, related to an adjustment of processing resources (as reflected by the P3) as well as the voluntary re-orientation of attention (RON) are functions mediated by prefrontal cortical areas. These are strongly modulated by dopaminergic projections (e.g., Nieoullon, 2002; Seamans and Yang, 2004). Because of the modulatory effects of T. gondii on the dopaminergic system it is therefore possible that only these latter cognitive subprocesses are modulated by latent T. gondii infection and may underlie deficits in goaldirected behavior. Given previous evidence of gender-specific effects of T. gondii infection (e.g., Flegr, 2008, 2012), we additionally analyzed whether these processes may differ between male and female individuals. 2. Methods
laboratory using the enzyme immunoassay Enzygnost Toxoplasmosis/IgG (Siemens Healthcare Diagnostics, Eschborn, Germany). The enzyme immunoassay was processed on a BEP III system (Siemens Healthcare Diagnostics). The sensitivity threshold of Enzygnost Toxoplasmosis/IgG is at least 6 UI/mL (Siemens Healthcare Diagnostics, 2010). For classification into T. gondii negative and positive subgroups, subjects with not detectable IgG antibody levels (n ¼ 36; serum level ¼ 0 UI/mL) were defined as negative, while those subjects with the highest concentration of IgG antibodies (n ¼ 36; mean serum level 152.1 UI/mL; range 54e510 UI/mL) were defined as positive (Fig. 1). The negative and positive subgroups did not differ significantly in gender distribution (according to a c2 test), or in age or level of education (according to 2way analyses of variance [ANOVAs] with between-subject factors group and gender; Table 1). Except for a measure of attentional endurance (assessed by the d2 test; Brickenkamp, 1994), ANOVAs applied to assess the neuropsychological characteristics of the participants did not indicate the significance between-group differences (all p > 0.05; Table 1) in depression (assessed by Becks Depression Inventory; Beck et al., 1961), cognitive failures (assessed by the Cognitive Failures Questionnaire; Broadbent et al., 1982), general cognitive status (assessed by the Mini Mental State Examination; Folstein et al., 1975), visual attention and task switching (assessed by the Trail Making Test; Reitan, 1958), spatial representation (assessed by a mental rotation task; Kersting et al., 2008), or crystalline intelligence (assessed by the Multiple choice Word Test, MWT-B; Lehrl, 1995). Nor there were any significant interactions of group and gender. All participants were informed about the scope of the study and gave written informed consent before any study protocol was commenced. However, the result of the immunoassay on T. gondii specific IgG antibodies was unknown to the participants of the study and to the operators who performed the cognitive testing, as the identification of T. gondii in the participants was conducted after the cognitive testing was finished. All participants gave written informed consent before any study protocol was commenced. They received a payment for their participation. The study conformed to the Code of Ethics of the World Medical Association (Declaration of Helsinki) and was approved by the Institutional Review Board. 2.2. Stimuli, task, and procedure Auditory stimuli were generated digitally using CoolEdit 2000 (Syntrillium Software Co, Phoenix, AZ, USA), and were presented binaurally using stereo headphones (AKG, K271 Studio) at the
A total of 131 healthy volunteers (mean age 70.3 years; range 63e88 years; 87 women) took part in the study. The participants were recruited through a number of newspaper advertisements and flyers distributed in the city of Dortmund (Germany). All data were gathered as part of a training study with a pre- and a postmeasure (for details: Gajewski and Falkenstein, 2012), with only the pre-measure data being reported here. The data of 7 participants were excluded from further analyses because of poor quality of the electroencephalography (EEG) and electro-oculography (EOG) data: 4 data sets showed high alpha activity, and in 3 data sets EOG channels were missing so that ocular artifacts correction was not possible. Identification of Toxoplasma-negative and -positive subjects without any clinical symptoms of acute toxoplasmosis was performed according to the following procedure: venous blood of all individuals was sampled and tested for T. gondii specific IgG antibodies. The analyses were performed in a certified local clinical
Anti-Toxoplasma IgG level [UI/ml]
2.1. Participants
600 male female
500 400 300 200 100 0 1
5
10
15
20
25
30
35
Subject Fig. 1. Individual anti-Toxoplasma IgG concentration of each serum positive participant, shown separately for male and female subjects.
C. Beste et al. / Neurobiology of Aging 35 (2014) 1037e1044
1039
Table 1 Sample characteristics and results of the sociodemographical and neuropsychological assessment for the IgG negative and IgG positive groups, shown separately for male and female subjects Gender
T. gondii gender
Male
Female
Male
Female
df
F
F
F
n ¼ 11 68.7 (1.1) 2.4 (0.3) 4.7 (0.8) 28.9 (3.7)
n ¼ 25 70.2 (0.7) 2.6 (0.4) 6.3 (1.2) 27.6 (2.5)
n ¼ 12 70.2 (1.0) 2,7 (0.3) 5.9 (0.8) 27.7 (3.7)
n ¼ 24 70.1(0.7) 3.0 (0.4) 5.0 (1.1) 31.3 (2.5)
72 71 72 71
0.46 0.88 0.01 0.16
0.74 0.79 0.12 0.14
0.74 0.02 1.56 0.64
383.2 (22.5) 20.9 (5.3) 2.1 (1.9)
405.5 (14.9) 24.0 (3.5) 3.0 (1.3)
378.3 (22.5) 20.0 (5.3) 3.6 (1.9)
398.7 (16.3) 20.8 (3.8) 9.0 (1.4)
68 68 68
0.07 0.20 5.10a
1.23 0.19 3.56
0.01 0.06 1,73
7.8 (1.0) 6.8 (0.9) 28.6 (0.3)
5.8 (0.7) 6.0 (0.6) 28.6 (0.5)
7.4 (1.0) 7.0 (0.9) 28.4 (0.3)
5.6 (0.7) 4.6 (0.6) 29.1 (0.5)
71 66 72
0.16 0.58 0.09
4.82a 4.45a 0.60
0.02 0.99 1.02
30.5 (0.9) 115.1 (3.4)
31.1 (0.9) 117.0 (2.3)
32.4 (0.9) 120.8 (3.4)
31.3 (0.6) 115.6 (2.3)
71 71
1.68 0.57
0.10 0.33
1.15 1.48
38.0 (4.0) 103.6 (11.7)
39.2 (2.5) 91.0 (7.4)
37.8 (2.6) 95.9 (7.5)
70 70
0.20 0.01
0.16 0.51
0.01 0.36
IgG negative
Number Age (y) Mean level of educationa BDI CFQa total score D2a Total number of symbols Number omitted symbols Number confused symbols Mental rotationa Total number Number correct MMSE MWT-Ba Number total IQ TMTa TMT-A TMT-B
IgG positive
36.4 (3.8) 97.1 (11.1)
T. gondii
Key: BDI, Beck Depression Inventory; CFQ, Cognitive Failures Questionnaire; D2, Test of Attention; Mean Level of Education: No degree (1) Primary; (2) Secondary general; (3) Intermediate secondary; (4) Gymnasium; MMSE, Mini Mental State Examination; MWT-B, multiple-choice word test, test of premorbid intelligence; T. gondii, Toxoplasma gondii; TMT, Trail Making Test. a Reduced number of participants. Significance level was set at p < 0.05.
intensity of 70 dB(A). They consisted of sine waves composed of base frequencies of either 500 Hz, 1000 Hz, or 2000 Hz. The stimuli were short (200 ms) and long (400 ms) tones (both including 5 ms rise and 5 ms fall times) presented equiprobably. Eighty percentages of these long and short tones were frequent standard stimuli (1000 Hz), and 20% were rare deviant stimuli (either 500 Hz or 2000 Hz, each 10%). The sequence of standard and deviant stimuli was pseudo-randomized. During testing, the participants sat on a comfortable chair in a dimly lit and quite room. A 2-alternative forced-choice duration discrimination task was used, in which the participants had to press 1 response button for short and the other for long tones irrespective of the pitch of the tone. The response buttons were held in the subject’s hands. The duration-hand contingency was counterbalanced between participants. Participants were instructed to respond in a fast but accurate manner. To avoid EEG alpha-activity and wandering eye-movements during the recordings, participants were instructed to keep their eyes open and to focus on a visual fixation point presented on a monitor placed in front of them. No feedback was given to the participants at any time during the experiment. To secure that the participants were able to reliably distinguish the tone pitches of the frequent and deviant stimuli, samples of the tones were presented and the participants were asked whether they hear the sounds, and whether they perceive the differences in pitch. All participants performed this task without any problems. Then, the participants carried out a short training until the task was familiar. Finally, all participants completed 2 test blocks interrupted by a rest break. A test block consisted of 120 trials (48 short and 48 long standard tones and 12 short and 12 long deviant tones). The stimulus onset asynchrony was 1400 ms. The timing of the stimuli and the recording of the participants’ responses were controlled by custom-written software. Reaction times (RTs) were measured by a high-resolution timer interface connected with the external response buttons. 2.3. Data recording The continuous EEG (amplifier bandpass 0.01e140 Hz) was sampled at 2048 Hz using 32 Ag/AgCl electrodes mounted on an
elastic cap according to the extended 10e20 system. The montage included 8 midline sites and 12 sites on each hemisphere. Horizontal and vertical eye positions were recorded by EOG using 4 electrodes positioned around both eyes. The ground electrode was placed on the center of the forehead, just above the nasion. Two additional electrodes were placed on the left and right mastoids (M1 and M2). Electrode impedance was kept below 10 kU. The raw data were offline downscaled to a sampling rate of 1000 Hz, bandpass filtered (cut-off frequencies 0.05 and 17 Hz), re-referenced to linked mastoids, and segmented into 1300-ms stimulus-locked epochs covering the period from 100 to 1200 ms relative to tone onset, using the BrainVision Analyzer software (version 1.05; Brain Products, Munich, Germany). The data were corrected for ocular artifacts using the Gratton and Coles procedure (Gratton et al., 1983). Individual epochs exceeding a maximum-minimum difference of 300 mV were excluded from further analysis (automatic artifact rejection as implemented in the BrainVision Analyzer software). The remaining epochs were baseline corrected with reference to a 100-ms prestimulus window, and averaged for each participant, separately for epochs with the deviant tones (averaged across the 500-Hz and 2000-Hz stimuli) and the standard tones. Trials with short and long tones were pooled, and averaged across the 2 test blocks to improve the signal-to-noise ratio of the EEG signal. Finally, difference waves were calculated (deviant minus standard) to analyze the deviance-related MMN, P3a, and RON components. 2.4. Data analysis Behavioral and ERP data were analyzed for standard and deviant tones. RT was defined as the time between the offset of the 200-ms tone and the push of a response button. Individual RTs of less than 100 ms and longer than 1200 ms, as well as error trials were excluded from further analysis. Rates of correct responses and mean RTs were subjected to 3-way ANOVAs with between-subject factors group (IgG negative vs. IgG positive) and gender (male vs. female), and within-subject factor stimulus (deviant vs. standard tones). In addition, the deviance-related distraction effect was defined as the percentage change in discrimination accuracy and
1040
C. Beste et al. / Neurobiology of Aging 35 (2014) 1037e1044
speed. It corresponds to (deviant standard tones)/standard tones 100, with deviant tones representing the correct responses and RTs to deviant tones and standard tones representing correct responses and RTs to standard tones. The ERP analysis was restricted to midline electrodes (Fz, FCz, Cz, and Pz) chosen to be commensurate with previous knowledge of the topographical scalp distribution of specific ERPs (review: Barrett et al., 1987; Näätänen and Picton, 1987; Polich, 2007), indicating that the N1, MMN, P3a, RON typically peak over frontocentral areas (FCz), the P2 over central areas (Cz), and the P3b over parietal areas (Pz) of the scalp. Peak amplitudes and latencies of these components were defined as their local maximum positivity or negativity within a particular latency window (N1 at FCz: 50e150 ms; MMN at FCz: 100e200 ms; P2 at Cz: 120e220 ms; P3a at FCz: 225e400 ms; P3b at Pz: 400e700 ms; RON at FCz: 400e700
3.1. Behavioral data IgG negative and positive participants did not differ significantly in the rate of correct responses, while both groups produced fewer correct responses to deviant tones than standard tones (Fig. 2A). The
100 95 90 85 80 75 70 65 0 Standard Deviant Tones
female Correct Responses [%]
male
B Response Times [ms]
3. Results
100 95 90 85 80 75 70 65 0 Standard Deviant Tones
male 550 525 500 475 450 425 400 375
female Response Times [ms]
Correct Responses [%]
A
ms after tone onset). The amplitudes and latencies of these components were subjected to 2-way ANOVAs with between-subject factors group and gender. Levene’s test was used to assess the homogeneity of variance, and the degrees of freedom were adjusted if variances were unequal. Effect sizes were computed to provide a more accurate interpretation of the practical significance of the findings, using the partial eta-squared coefficient.
0
550 525 500 475 450 425 400 375 0 Standard Deviant Tones
Standard Deviant Tones
C
D Change in Response Time [%]
Change [%]
15 12 9 6 3 0 Correct Responses
Response Times
IgG negative IgG positive
50 40 30 20 10 0 -10
r = 0.38 p < 0.05
100 200 300 400 500 Toxoplasma Toxoplasma IgGSerum antibody Concentration Serum Concentration [UI/ml]
0
Fig. 2. (A) Rates of correct responses and (B) response times for IgG serum negative and positive participants, shown separately for the frequent standard tones and the rare deviant tones, and for male and female participants. (C) Deviance-related percentage changes (deviant tones relative to standard tones) for IgG serum negative and positive participants (averaged across males and females), shown for the frequent standard tones and the rare deviant tones. Error bars indicate standard errors across participants (N ¼ 36). (D) Percentage change in response times as function of anti-Toxoplasma IgG concentrations for each serum positive participants (averaged across males and females) with linear regression line.
C. Beste et al. / Neurobiology of Aging 35 (2014) 1037e1044
ANOVA indicated a main effect of stimulus (F [1,68] ¼ 40.35; p < 0.001; partial ɳ2 ¼ 0.37), but no main effect of group (F [1,68] ¼ 0.14; p > 0.05; partial ɳ2 ¼ 0.00) or stimulus group interaction (F [1,68] ¼ 0.01; p > 0.05; partial ɳ2 ¼ 0.00). There were no interactions of group and gender (F [1,68] ¼ 0.24) or stimulus, group, and gender (F [1,68] ¼ 0.59; both p > 0.05; both partial ɳ2 < 0.01), while a main effect of gender (F [1,68] ¼ 6.42; p < 0.05; partial ɳ2 ¼ 0.09) indicated less correct responses of female than of male participants. RTs to deviant tones were significantly increased, relative to standard tones (Fig. 2B), as indicated by a main effect of stimulus (F [1,68] ¼ 61.68; p < 0.001; partial ɳ2 ¼ 0.48). Most importantly, while both groups did not differ in RTs per second, the deviance-related increase in RTs was more pronounced in the IgG positive, than IgG negative, group. Thus, there was a significant stimulus group interaction (F [1,68] ¼ 5.46; p < 0.05; partial ɳ2 ¼ 0.07), but no main effect of group (F [1,68] ¼ 1.63; p > 0.05; partial ɳ2 ¼ 0.02). The ANOVA also revealed a significant group gender interaction (F [1,68] ¼ 5.44; p < 0.05; partial ɳ2 ¼ 0.07): In the male group, RTs were larger in IgG positive, than IgG negative, participants (t [21] ¼ 2.87; p < 0.01), while RTs did not differ between IgG positive and IgG negative participant in the female group (t [21] ¼ 0.86; p > 0.05). There was no significant interaction of stimulus and gender (F [1,68] ¼ 0.85) and no significant main effect of gender (F [1,68] ¼ 0.38; both p > 0.05; both partial ɳ2 < 0.02). Also, there was no significant interaction of stimulus, group, and gender (F [1,68] ¼ 0.15, p > 0.05; partial ɳ2 < 0.01), suggesting that the more pronounced deviance-related increase in RTs in the IgG positive, than IgG negative, group did not depend on gender. Thus, taken male and female subjects together, it appeared that the IgG positive and IgG negative groups did not differ in the deviance-related decrease in correct responses (Fig. 2C; F [1,68] ¼ 0.04; p > 0.05; partial ɳ2 ¼ 0.00), whereas IgG positive participants showed a stronger increase in RTs than their IgG negative counterparts (F [1,70] ¼ 4.75; p < 0.05; partial ɳ2 ¼ 0.06). In addition to this between-group difference, there was a positive correlation of individual anti-Toxoplasma IgG concentrations and RT increase within the IgG positive group (Fig. 2D), indicating that higher anti-Toxoplasma IgG concentrations were associated with delayed duration discrimination of deviant tones. 3.2. ERPs Standard tones produced a typical fronto-central N1-P2 complex peaking at 95 ms and 183 ms, respectively, and a pronounced parietal P3b peaking at about 600 ms (Fig. 3A). In contrast, deviant tones produced, beside a fronto-central N1 and a parietal P3b, a strong fronto-central positivity at about 300 ms after tone onset. The difference waveforms (deviant minus standard tones, Fig. 3B) indicated a fronto-central MMN (peaking at 138 ms), P3a (peaking at 304 ms), and RON (peaking at 521 ms after tone onset). The ERPs to standard tones (N1, P2, P3b) did not differ significantly between groups, neither in amplitudes nor latencies (Table 2), while amplitudes of P2 and P3b were larger in female than in male participants. Also, the N1 response to deviant tones did not differ between groups. However, the analysis of the difference waveforms revealed significantly delayed P3a and RON responses in IgG positive, relative to IgG negative, participants. No significant differences occurred in P3a and RON amplitudes, or in MMN amplitudes or latencies. Also, there were no group gender interactions, neither for ERPs to standard tones, nor for the difference waveforms. In sum, while the 2 groups did not differ in the processing of standard tones, the deviance-related fronto-central positivity P3a and RON components were delayed in the IgG positive group. An additional correlation analysis did not indicate significant correlations of ERPs and individual anti-Toxoplasma IgG concentrations
1041
within the IgG positive group (all p > 0.05), except for a slight positive correlation of IgG concentrations and P3a amplitude (p ¼ 0.054; Bonferroni-corrected value). 4. Discussion In the present study we examined the role of latent T. gondii infection as a modulator for goal-directed behavior in healthy elderly individuals. The results show that latent T. gondii infection compromises goal-directed behavior. Using an auditory distraction paradigm we show that elderly individuals with positive IgG Toxoplasma serum concentrations revealed slower RTs, when confronted with deviant stimuli. No effects of T. gondii infection were evident on standard trials. The effects at the behavioral level were predictable on the basis of individual anti-Toxoplasma IgG concentrations. Higher concentrations were related to longer reaction times on deviant trials. This suggests that declines in goal-directed behavior under auditory distraction are directly related to the effects of T. gondii. The neurophysiological data suggest that these behavioral deficits emerge as a consequence of specific effects of T. gondii on a subset of cognitive processes mediating goal-directed behavior. The ERP data show that T. gondii did not affect amplitude and latency of the N1 and P2, as well as the mismatch negativity MMN. This suggests that attentional selection mechanisms, as reflected by the N1 and P2 (e.g., Herrmann and Knight, 2001; Potts, 2004) are not modulated and do therefore not contribute to the observed slowing in RTs on deviant trials. Similarly, the results suggest that auditory sensory memory processes (reflected by the MMN, e.g., Näätänen et al., 2012) are not modulated by T. gondii. This suggests that T. gondii does not affect the ability of pre-attentive processes detecting differences in incoming sensory information. However, for the P3a as well as for the RON, shifts in latency were evident in T. gondii IgG serum positive elderly individuals. No effects were evident for the amplitudes. The P3a has been suggested to reflect processes of attentional allocation (Hölig and Berti, 2010; Polich, 2007). In deviant trials the P3a may reflect a mechanism of attentional disengagement (Berti, 2008). In this sense, the P3a reflects attentional allocation processes and shifts or switches in attention (e.g.,Escera and Corral, 2007; Escera et al., 2000; Schröger, 1996). The longer latency of the P3a in IgG serum positive elderly individuals suggests that these involuntary processes take longer to become fully effective. As a consequence of this longer latency to activate additional processing resources under auditory distraction, behavioral performance, and goal-directed behavior become deficient. However, the results show that also the RON revealed a prolonged latency in IgG serum positive elderly individuals. The RON has been suggested to reflect the reorientation of attention after distraction (e.g., Schröger et al., 2000). Yet, it is likely that the prolonged RON latency reflects a simple aftereffect of the prolonged P3a latency. The P3a precedes the RON. A shift in latency of the P3a therefore most likely affects the RON latency. Corroborating this interpretation that the RON latency shift does not reflect a “real” effect of different Toxoplasma IgG levels in elderly individuals, the behavioral data on standard trials were not different between the groups. A latency shift in RON would imply that re-orientation processes toward standard trials are deficient. This would most likely entail longer reaction times on standard trials, too, as found in a number of studies (see Flegr, 2013 for overview). It may be regarded counterintuitive why T. gondii, is known to increase dopaminergic turnover, confers negative effects on goaldirected behavior. However, network characteristics in prefrontal cortices, which are important for goal-directed behavior, strongly vary depending on the relative influence of D1 versus D2-receptor
1042
C. Beste et al. / Neurobiology of Aging 35 (2014) 1037e1044
A
B
ERPs
Deviant-Standard Differences
Fz
Fz
P2
FCz
P3a
FCz
MMN
RON
N1 Cz
Cz
P3b
Pz
Pz
2 µV
+ 200 ms
Standards, IgG negative Deviants, IgG negative Standards, IgG positive Deviants, IgG positive
IgG negative IgG positive
Fig. 3. Grand average ERPs of the frequent standard tones and the rare deviant tones (A), and difference waves (B, deviant minus standard tones) at Fz, FCz, Cz, and Pz, shown for IgG serum negative and positive participants (averaged across males and females). The vertical lines reflect the onset of the tone stimulus. ERP components (N1, P2, P3a, P3b, MMN, and RON) are marked at the waveform of maximal amplitude. Abbreviations: ERP, event-related potential; MMN, mismatch negativity; RON, re-orienting negativity.
related neural transmission (Durstewitz and Seamans, 2008; Seamans and Yang, 2004). A highly active dopamine D2 system has been shown to allow the establishment of multiple representations in prefrontal cortical networks and working memory, that is the processing capacity of the network is increased. This state is more responsive and flexible, but also more interference-prone compared with a network state dominated by high dopamine D1 receptor turnover (Durstewitz and Seamans, 2008). The task
applied specifically examines the robustness of representations against interference. It has been shown previously that haloperidol, a D2-receptor antagonist is able to suppress effects of T. gondii infection (Webster et al., 2006; Gajewski et al., submitted). It is therefore likely that especially dopaminergic neural transmission mediated via D2 receptors in enhanced in latent T. gondii infection. Given this, it is plausible that especially the distracting deviant trials show effects of latent T. gondii infection. In a previous study,
C. Beste et al. / Neurobiology of Aging 35 (2014) 1037e1044
1043
Table 2 Mean amplitudes (Amp. in mV) and latencies (Lat. in ms) and standard error of means of the event-related potentials of IgG serum negative and positive participants for standard and deviant tones, shown separately for males and females, with F statistics and effect sizes. Mismatch negativity (MMN), P3a, and re-orienting negativity (RON) refer to the difference event-related potentials (deviant minus standard tones) IgG negative Male Standard tones N1 Amp. P2 Amp. P3b Amp. N1 Lat. P2 Lat P3b Lat. Deviant tones N1 Amp. MMN Amp. P3a Amp. RON Amp. N1 Lat. MMN Lat. P3a Lat. RON Lat.
IgG positive Female
Male
T. gondii Female
F1,
72
T. gondii gender
Gender ɳ2p
F1,
72
ɳ2p
F1,
72
ɳ2p
4.2 1.8 3.9 94.4 173.2 607.5
(0.7) (0.7) (0.7) (2.3) (6.6) (14.1)
4.3 2.7 4.8 94.0 173.9 622.9
(0.5) (0.4) (0.5) (1.5) (4.4) (9.3)
3.9 1.2 2.8 94.3 174.4 611.3
(0.7) (0.6) (0.7) (2.3) (6.3) (13.5)
3.9 3.2 4.5 91.2 176.5 605.9
(0.5) (0.4) (0.5) (1.6) (4.5) (9.2)
0.33 0.07 1.49 0.57 0.11 0.32
0.01 0.00 0.02 0.01 0.01 0.01
0.01 6.89* 4.96* 0.82 0.06 0.18
0.00 0.09 0.07 0.01 0.01 0.01
0.01 0.94 0.59 0.54 0.02 0.78
0.00 0.01 0.01 0.01 0.00 0.01
4.5 1.5 3.7 2.4 98.2 137.2 294.6 481.5
(0.8) (0.6) (0.7) (0.7) (3.7) (8.5) (11.4) (19.2)
5.3 2.3 4.6 2.8 96.7 143.0 289.2 539.8
(0.5) (0.4) (0.4) (0.5) (2.5) (5.7) (7.6) (12.8)
4.5 1.4 3.3 2.8 96.8 134.2 316.4 560.2
(0.8) (0.6) (0.6) (0.5) (3.5) (8.2) (10.9) (18.1)
4.7 2.3 4.0 2.5 97.0 140.3 323.0 564.1
(0.6) (0.4) (0.4) (0.5) (2.5) (5.8) (7.7) (13.0)
0.20 0.00 0.78 0.01 0.03 0.16 8.48** 10.19**
0.01 0.00 0.01 0.00 0.00 0.01 0.11 0.13
0.41 2.41 2.46 0.04 0.05 0.70 0.01 3.73
0.01 0.03 0.04 0.01 0.01 0.01 0.00 0.05
0.16 0.01 0.05 0.35 0.07 0.01 0.39 2.85
0.01 0.00 0.01 0.01 0.00 0.00 0.01 0.04
Key: MMN, mismatch negativity; RON, re-orienting negativity; T. gondii, Toxoplasma gondii. * p < 0.05, ** p < 0.01.
we found that infected individuals showed a clear impairment in different memory functions, while executive functions operating with visual stimuli in the Stroop task (inhibition) and the trails B task (shifting) were not affected. However, attention-related functions with auditory stimuli were not examined in that study (Gajewski et al., 2014). With respect to the interpretation of the results in relation to the dopaminergic system it is important to note that even in the stage of latent T. gondii infection, the dopamine system is affected. Subjects tested are not in the stage of acute of infection, but in the stage of latent infection. This stage (cysts [bradyzoites] stage) is indicated by the positive IgG marker and these cysts persist lifelong in host tissues (e.g., Robert-Gangneux and Darde, 2012). Importantly, Prandovszky et al. (2011) showed that in exactly this “cyst stage” (i.e., where no acute T. gondii infection is evident, but a latent T. gondii infection is evident) in chronically infected mice brains, parasite cysts contained high levels of dopamine based on staining with a commercial antibody specific to dopamine (for review: McConkey et al., 2013). This study clearly shows that the interaction of T. gondii with the dopamine system is not limited to the stage of acute infection, but rather persists in the stage of chronic infection. In their in vitro study Prandovszky et al. (2011) showed that “dopamine release increased in infected cultures in a dosedependent manner with the number of parasites in the culture correlating with the amount of dopamine released” (p. 5). However, it has to be noted that 1 animal study did not account for T. gondii induced changes in the dopamine system (Goodwin et al., 2012). Goodwin et al. (2012) did also not account for behavioral changes, even though most results in the field clearly demonstrate such changes. Hence, the mechanism that dopamine may be the critical factor influenced by T. gondii has to be treated with some caution. However, with respect to the possible neuronal mechanism it has further to be noted that an effect of T. gondii in the behavioral data (i.e., larger RTs in IgG positive, than IgG negative, participants) was evident in men, but not in women, which corroborates data by Flegr et al. (2008). Flegr et al. (2008) noted that this may be because of the hormonal status relating to varying levels in different steroid hormones. This does not foreclose the previously mentioned interpretation suggesting that the dopamine system plays an important role, because steorid hormones are well-known to modulate dopaminergic neural transmission (for review: Zheng et al., 2009).
In summary, the study shows that latent T. gondii infection modulates goal-directed behavior in otherwise healthy elderly individuals. The individual IgG antibody serum concentration was predictive for behavioral performance in goal-directed behavior. The effects of T. gondii are restricted to a subset of cognitive processes mediating goal-directed behavior. In particular processes related to attentional allocation of processing resources. Other processes like bottom-up attentional processes or sensory memory processes are not affected. This dissociated pattern of results may emerge as a consequence of a differential relevance of the dopaminergic systems for these cognitive subprocesses. The results show that latent T. gondii infection is an important neurobiological modulator that needs to be taken into account when examining cognitive functions in elderly individuals. Disclosure statement All authors disclose no actual or potential conflicts of interest including any financial, personal, or other relationships with other people or organizations that could inappropriately influence (bias) their work. Acknowledgements We thank the participants, Ludger Blanke, Pia Deltenre, Brita Rietdorf, Claudia Wipking, Kirsten Liesenhoff-Henze, Marion Page, and Claudia Schulte-Dahmann for excellent technical and organizational assistance, and Dr Meinolf Blaszkewicz for his support. This work was funded by a grant from the German Insurance Association (GDV, Gesamtverband der Deutschen Versicherungswirtschaft) to P.G. and M.F., and by a Grant from the Deutsche Forschungsgemeinschaft (DFG) to C.B. (BE 4045/10-1) and S.G. (GE 1920/3-1). References Bäckman, L., Lindenberger, U., Li, S.C., Nyberg, L., 2010. Linking cognitive aging to alterations in dopamine neurotransmitter functioning: recent data and future avenues. Neurosci. Biobehav. Rev. 34, 670e677. Barrett, G., Neshige, R., Shibasaki, H., 1987. Human auditory and somatosensory event-related potentials: effects of response condition and age. Electroencephalogr. Clin. Neurophysiol. 66, 409e419. Beck, A.T., Ward, C.H., Mendelson, M., Mock, J., Erbaugh, J., 1961. An inventory for measuring depression. Arch. Gen. Psychiatry 4, 561e571.
1044
C. Beste et al. / Neurobiology of Aging 35 (2014) 1037e1044
Berti, S., 2008. Cognitive control after distraction: event-related brain potentials (ERPs) dissociate between different processes of attentional allocation. Psychophysiology 45, 608e620. Beste, C., Stock, A.K., Ness, V., Epplen, J.T., Arning, L., 2012. Differential effects of ADORA2A gene variations in pre-attentive visual sensory memory subprocesses. Eur. Neuropsychopharmacol. 22, 555e561. Beste, C., Schneider, D., Epplen, J.T., Arning, L., 2011. The functional BDNF Val66Met polymorphism affects functions of pre-attentive visual sensory memory processes. Neuropharmacology 60, 467e471. Beste, C., Domschke, K., Kolev, V., Yordanova, J., Baffa, A., Falkenstein, M., Konrad, C., 2009. Functional 5-HT1a receptor polymorphism selectively modulates errorspecific subprocesses of performance monitoring. Hum. Brain Mapp. 31, 621e630. Beste, C., Saft, C., Güntürkün, O., Falkenstein, M., 2008. Increased cognitive functioning in symptomatic Huntington’s disease as revealed by behavioral and event-related potential indices of auditory sensory memory and attention. J. Neurosci. 28, 11695e11702. Brickenkamp, R., 1994. Test d2, Aufmerksamkeits-belastungs-test, eighth ed. Hogrefe, Goettingen. Broadbent, D.E., Cooper, P.F., FitzGerald, P., Parkes, K.R., 1982. The cognitive failures questionnaire (CFQ) and its correlates. Br. J. Clin. Psychol. 21, 1e16. Buckner, R.L., 2004. Memory and executive function in aging and AD: multiple factors that cause decline and reserve factors that compensate. Neuron 30, 195e208. Durstewitz, D., Seamans, J.K., 2008. The dual-state theory of prefrontal cortex dopamine function with relevance to catechol-o-methyltransferase genotypes and schizophrenia. Biol. Psychiatry 64, 739e749. Escera, C., Alho, K., Schröger, E., Winkler, I., 2000. Involuntary attention and distractibility as evaluated with event-related brain potentials. Audiol. Neurootol. 5, 151e166. Escera, C., Corral, M.J., 2007. Role of mismatch negativity and novelty-P3 in involuntary auditory attention. J. Psychophysiol. 21, 251e264. Flegr, J., 2007. Effects of toxoplasma on human behavior. Schizophr. Bull. 33, 757e760. Flegr, J., Novotná, M., Lindová, J., Havlí cek, J., 2008. Neurophysiological effect of the Rh factor. Protective role of the RhD molecule against Toxoplasma-induced impairment of reaction times in women. Neuro. Endocrinol. Lett. 29, 475e481. ski, M., Deptu1a, A., Zalas-Wie˛ cek, P., Piskunowicz, M., Flegr, J., Guenter, W., Bielin ski, A., Gospodarek, E., Borkowska, A., 2012. Toxoplasma gondii Szwed, K., Bucin infection affects cognitive function e corrigendum. Folia Parasit. 59, 253e254. Flegr, J., 2013. Influence of latent Toxoplasma infection on human personality, physiology and morphology: pros and cons of the Toxoplasma-human model in studying the manipulation hypothesis. J. Exp. Biol. 216, 127e133. Fillenz, M., 1993. Short-term control of transmitter synthesis in central catecholaminergic neurones. Prog. Biophys. Mol. Biol. 60, 29e46. Folstein, M.F., Folstein, S.E., McHugh, P.R., 1975. “Mini-mental state”. A practical method for grading the cognitive state of patients for the clinician. J. Psychiatr. Res. 12, 189e198. Gajewski, P.D., Hengstler, J.G., Falkenstein, M., Golka, K., 2014. Toxoplasma gondii impairs memory in infected seniors. Brain Behav. Immun. 36, 193e199. Gajewski, P.D., Falkenstein, M., 2012. Training-induced improvement of response selection and error detection in aging assessed by task switching: effects of cognitive, physical, and relaxation training. Front. Hum. Neurosci. 6, 130. Gatkowska, J., Wieczorek, M., Dziadek, B., Dzitko, K., Dlugonska, H., 2012. Behavioral changes in mice caused by Toxoplasma gondii invasion of brain. Parasitol. Res. 111, 53e58. Gaskell, E.A., Smith, J.E., Pinney, J.W., Westhead, D.R., McConkey, G.A., 2009. A unique dual activity amino acid hydroxylase in Toxoplasma gondii. PLoS One 4, e4801. Getzmann, S., Gajewski, P.D., Hengstler, J.G., Falkenstein, M., Beste, C., 2013a. BDNF Val66Met polymorphism and goal-directed behaviour in healthy elderly e evidence from auditory distraction. NeuroImage 64, 290e298. Getzmann, S., Gajewski, P.D., Falkenstein, M., 2013b. Does age increase auditory distraction? Electrophysiological correlates of high and low performance in seniors. Neurobiol. Aging 34, 1952e1962. Goodwin, D., Hrubec, T.C., Klein, B.G., Strobl, J.S., Werre, S.R., Han, Q., Zajac, A.M., Lindsay, D.S., 2012. Congenital infection of mice with Toxoplasma gondii induces minimal change in behavior and no change in neurotransmitter concentrations. J. Parasitol. 98, 706e712. Gratton, G., Coles, M.G.H., Donchin, E., 1983. A new method for off-line removal of ocular artifact. Electroencephalogr. Clin. Neurophysiol. 55, 468e484. Herrmann, C.S., Knight, R.T., 2001. Mechanisms of human attention: event-related potentials and oscillations. Neurosci. Biobehav. Rev. 25, 465e476. Hoelig, C., Berti, S., 2010. To switch or not to switch: brain potential indices of attentional control after task-relevant and task-irrelevant changes of stimulus features. Brain Res. 1345, 164e174. Horváth, J., Czigler, I., Birkás, E., Winkler, I., Gervai, J., 2009. Age-related differences in distraction and reorientation in an auditory task. Neurobiol. Aging 30, 1157e1172. Javitt, D.C., Steinschneider, M., Schroeder, C.E., Arezzo, J.C., 1996. Role of cortical Nmethyl-D-aspartate receptors in auditory sensory memory and mismatch
negativity generation: implications for schizophrenia. Proc. Natl. Acad. Sci. U.S.A 93, 11962e11967. Kersting, M., Althoff, K., Jäger, A.O., 2008. WIT-2. Der Wilde-Intelligenztest. Verfahrenshinweise. Hogrefe, Göttingen. Kropotov, J.D., Alho, K., Näätänen, R., Ponomarev, V.A., Kropotova, O.V., Anichkov, A.D., Nechaev, V.B., 2000. Human auditory-cortex mechanisms of preattentive sound discrimination. Neurosci. Lett. 280, 87e90. Lehrl, S., 1995. Mehrfach-Wortwahl-Test (MWT). Medizinische Verlagsgesellschaft, Erlangen. McConkey, G.A., Martin, H.L., Bristow, G.C., Webster, J.P., 2013. Toxoplasma gondii infection and behaviour: location, location, location? J. Exp. Biol. 216, 113e119. Miman, O., Kusbeci, O.Y., Aktepe, O.C., Cetinkaya, Z., 2010. The probable relation between Toxoplasma gondii and Parkinson’s disease. Neurosci. Lett. 475, 129e131. Näätänen, R., Kujala, T., Escera, C., Baldeweg, T., Kreegipuu, K., Carlson, S., Ponton, C., 2012. The mismatch negativity (MMN)ea unique window to disturbed central auditory processing in ageing and different clinical conditions. Clin. Neurophysiol. 123, 424e458. Näätänen, R., Picton, T.W., 1987. The N1 wave of the human electric and magnetic response to sound: a review and an analysis of the component structure. Psychophysiology 24, 375e425. Nagy, A., Paroczy, Z., Norita, M., Benedek, G., 2005. Multisensory responses and receptive field properties of neurons in the substantia nigra and in the caudate nucleus. Eur. J. Neurosci. 22, 419e424. Nieoullon, A., 2002. Dopamine and the regulation of cognition and attention. Prog. Neurobiol. 67, 53e83. Polich, J., 2007. Updating P300: an integrative theory of P3a and P3b. Clin. Neurophysiol. 118, 2128e2148. Potts, G.F., 2004. An ERP index of task relevance evaluation of visual stimuli. Brain Cogn. 56, 5e13. Prandovszky, E., Gaskell, E., Martin, H., Dubey, J.P., Webster, J.P., McConkey, G.A., 2011. The neurotropic parasite Toxoplasma gondii increases dopamine metabolism. PLoS One 6, e23866. Reitan, R.M., 1958. Validity of the Trail Making Test as an indicator of organic brain damage. Percept. Mot. Skills 8, 271e276. Robert-Gangneux, F., Darde, M.L., 2012. Epidemiology of and diagnostic strategies for toxoplasmosis. Clin. Microbiol. Rev. 25, 264e296. Ruzzoli, M., Pirulli, C., Brignani, D., Maioli, C., Miniussi, C., 2012. Sensory memory during physiological aging indexed by mismatch negativity (MMN). Neurobiol. Aging 33, 625.e21e625.e30. Saft, C., Schüttke, A., Beste, C., Andrich, J., Heindel, W., Pfleiderer, B., 2008. fMRI reveals altered auditory processing in manifest and premanifest Huntington’s disease. Neuropsychologia 46, 1279e1289. Schröger, E., 1996. A neural mechanism for involuntary attention shifts to changes in auditory stimulation. J. Cogn. Neurosci. 8, 527e539. Schröger, E., Wolff, C., 1998. Attentional orienting and reorienting is indicated by human event-related brain potentials. Neuroreport 9, 3355e3358. Schröger, E., Giard, M.H., Wolff, C., 2000. Auditory distraction: event-related potential and behavioural indices. Clin. Neurophysiol. 111, 1450e1460. Seamans, J.K., Yang, C.R., 2004. The principal features and mechanisms of dopamine modulation in the prefrontal cortex. Prog. Neurobiol. 74, 1e58. Siemens Healthcare Diagnostics, 2010. Enzygnost Toxoplasmosis/IgG Edition September 2010. Tenter, A.M., Heckeroth, A.R., Weiss, L.M., 2000. Toxoplasma gondii: from animals to humans. Int. J. Parasitol. 30, 1217e1258. Turchi, J., Sarter, M., 2001. Bidirectional modulation of basal forebrain N-methyl-Daspartate receptor function differentially affects visual attention but not visual discrimination performance. Neuroscience 104, 407e417. Umbricht, D., Koller, R., Vollenweider, F.X., Schmid, L., 2002. Mismatch negativity predicts psychotic experiences induced by NMDA receptor antagonist in healthy volunteers. Biol. Psychiatry 51, 400e406. Webster, J.P., Lamberton, P.H., Donnelly, C.A., Torrey, E.F., 2006. Parasites as causative agents of human affective disorders? The impact of anti-psychotic, moodstabilizer and anti-parasite medication on Toxoplasma gondii’s ability to alter host behaviour. Proc. Biol. Sci. 273, 1023e1030. Webster, J.P., 2007. The effect of Toxoplasma gondii on animal behavior: playing cat and mouse. Schizophr. Bull. 33, 752e756. Webster, J.P., Kaushik, M., Bristow, G.C., McConkey, G.A., 2013. Toxoplasma gondii infection, from predation to schizophrenia: can animal behavior help us understand human behaviour? J. Exp. Biol. 216, 99e112. Willemssen, R., Falkenstein, M., Schwarz, M., Müller, T., Beste, C., 2011. Effects of aging, Parkinson’s disease, and dopaminergic medication on response selection and control. Neurobiol. Aging 32, 327e335. Zheng, P., 2009. Neuroactive steorif regulation of neurotransmitter release in the CNS: action, mechanism and possible significance. Prog. Neurobiol. 89, 134e152. Znamenskiy, P., Zador, A., 2013. Corticostriatal neurones in auditory cortex drive decisions during auditory discrimination. Nature 497, 482e486.
Contents lists available at ScienceDirect
Neurobiology of Aging journal homepage: www.elsevier.com/locate/neuaging
Latent Toxoplasma gondii infection leads to deficits in goal-directed behavior in healthy elderly Christian Beste a,1, Stephan Getzmann b, *,1, Patrick D. Gajewski b, Klaus Golka b, Michael Falkenstein b a b
Cognitive Neurophysiology, Department of Child and Adolescent Psychiatry, University of Dresden, Dresden, Germany Leibniz Research Centre for Working Environment and Human Factors at the Technical University of Dortmund (IfADo), Dortmund, Germany
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 August 2013 Received in revised form 11 November 2013 Accepted 13 November 2013 Available online 20 November 2013
Goal-directed behavior is well-known to show declines in elderly individuals, possibly because of alterations in dopaminergic neural transmission. The dopaminergic system is modulated by a number of other different factors. One of these factors, which has attracted a considerable amount of interest in neurobiology, but has only rarely been examined with respect to its possible modulatory role for cognitive functions in elderly individuals, is latent Toxoplasma gondii (T. gondii) infection. Latent T. gondii infection may be of relevance to goal-directed behavior as it alters dopaminergic neural transmission. We examine goal-directed behavior in T. gondii IgG positive and negative elderly subjects in auditory distraction paradigm. We apply event-related potentials to examine which cognitive subprocesses are affected by latent T. gondii infection on a neurophysiological level. We show that latent T. gondii infection compromises the management of auditory distraction in elderly by specifically delaying processes of attentional allocation and disengagement. The results show that latent T. gondii infection is neglected but an important neurobiological modulator of cognitive functions in elderly individuals. Ó 2014 Elsevier Inc. All rights reserved.
Keywords: Elderly individuals Aging Dopamine Cognitive flexibility Event-related potentials Toxoplasma gondii
1. Introduction Goal-directed behavior is orchestrated by a plenty of cognitive subprocesses and neurobiological systems. Very recent results provide conclusive evidence that the cortico-striatal system plays a pivotal role for goal-directed behavior based on auditory stimuli (Znamenskiy and Zador, 2013). Possibly this is the case because the striatum contains auditory sensory neurons (Nagy et al., 2005) likely involved in sound discrimination (Kropotov et al., 2000; Saft et al., 2008) and attentional control (Beste et al., 2008, 2009, 2011, 2012). These cortico-striatal circuits have frequently been shown to undergo degenerative changes in aging (e.g., Buckner, 2004), which likely underlies the susceptibility in elderly individuals to distracting stimuli from different sensory modalities leading to declines in goal-directed behavior (Getzmann et al., 2013a; Horvath et al., 2009; Ruzzoli et al., 2012). Besides changes in structural neuroanatomy, also changes in catecholaminergic neural * Corresponding author at: Leibniz Research Centre for Working Environment and Human Factors, Ardeystraße 67, D-44139 Dortmund, Germany. Tel.: þ49 231 1084 338; fax: þ49 231 1084 401. E-mail address: [email protected] (S. Getzmann). 1 Both authors contributed equally to this work and should be considered co-first authors. 0197-4580/$ e see front matter Ó 2014 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.neurobiolaging.2013.11.012
transmission occur in aging (for review: Bäckman et al., 2010). These changes in dopaminergic neural transmission contribute to deficits in goal-directed behavior in elderly individuals (e.g., Bäckman et al., 2010; Willemssen et al., 2011). However, the dopaminergic system is modulated by a number of different factors. One of these factors, which has attracted a considerable amount of interest in neurobiology, but has not been examined with respect to its possible modulatory role for cognitive functions in elderly individuals, is latent Toxoplasma gondii (T. gondii) infection. T. gondii is one of the most successful protozoan parasites on earth with an estimated prevalence of 30% in the world (Flegr, 2013; Tenter et al., 2000; Webster, 2007). T. gondii contains genes coding for tyrosine hydroxylase (Gaskell et al., 2009) needed to transform tyrosine into L-Dopa (e.g., Fillenz, 1993) in humans. T. gondii has thus been shown to increase the release of dopamine several-fold even after acute infection (McConkey et al., 2013; Prandovszky et al., 2011). Corroborating the role of T. gondii in dopaminergic neural transmission, it has been shown that T. gondii is related to the incidence of schizophrenia (e.g., Webster et al., 2007, 2013) and possibly Parkinson’s disease (Miman et al., 2010). Further evidence shows that haloperidol, a D2-receptor antagonist, is able to alleviate symptoms of acute T. gondii infection (Webster et al., 2006). Studies in healthy young humans suggest that even latent T. gondii infection leads to decreased performance in several
1038
C. Beste et al. / Neurobiology of Aging 35 (2014) 1037e1044
cognitive functions (Flegr, 2007, 2013). Similar results are also obtained in animal studies (e.g., Flegr, 2013; Gatkowska et al., 2012). It is therefore plausible that latent T. gondii infection leads to declines in goal-directed behavior in healthy elderly individuals. Because of the high prevalence, T. gondii infection status may be an important variable contributing to the high inter-individual differences in cognitive functions in elderly individuals. In the present study we use an auditory distraction paradigm and record event-related potentials (ERPs) to examine which cognitive subprocesses involved in goal-directed behavior are modulated by latent T. gondii infection in elderly individuals. In this paradigm a sequence of repeating short and long tones is presented, and distraction is induced by presenting stimuli at a pitch different from the usual tones. Subjects have to attend to a task-relevant tone feature (i.e., tone duration), while ignoring the deviant tone feature (i.e., tone pitch; e.g., Schröger and Wolf, 1998; Schröger et al., 2000). Processes related to stimulus detection are reflected in the P1 and N1 ERPs (e.g., Herrmann and Knight, 2001). The deviance in tone pitch is detected in sensory memory and reflected by the mismatch negativity (MMN) (for review: Näätänen et al., 2012). Subsequent mechanisms of attentional shifting toward the distractor and an adjustment of mental resources are reflected in the P3a (Escera et al., 2000; Getzmann et al., 2013b; Polich, 2007). Processes related to the recovery from distraction are reflected in the reorienting negativity (RON) (e.g., Schröger et al., 2000). T. gondii may in principle affect all of these subprocesses. However, mechanisms related to bottom-up stimulus detection (P1 and N1), and especially sensory memory processes (MMN) have been shown to strongly depend on glutamatergic neural transmission (Beste et al., 2008; Javitt et al., 1996; Turchi and Sarter, 2001; Umbricht et al., 2002). On the contrary, working memory and central executive processes, related to an adjustment of processing resources (as reflected by the P3) as well as the voluntary re-orientation of attention (RON) are functions mediated by prefrontal cortical areas. These are strongly modulated by dopaminergic projections (e.g., Nieoullon, 2002; Seamans and Yang, 2004). Because of the modulatory effects of T. gondii on the dopaminergic system it is therefore possible that only these latter cognitive subprocesses are modulated by latent T. gondii infection and may underlie deficits in goaldirected behavior. Given previous evidence of gender-specific effects of T. gondii infection (e.g., Flegr, 2008, 2012), we additionally analyzed whether these processes may differ between male and female individuals. 2. Methods
laboratory using the enzyme immunoassay Enzygnost Toxoplasmosis/IgG (Siemens Healthcare Diagnostics, Eschborn, Germany). The enzyme immunoassay was processed on a BEP III system (Siemens Healthcare Diagnostics). The sensitivity threshold of Enzygnost Toxoplasmosis/IgG is at least 6 UI/mL (Siemens Healthcare Diagnostics, 2010). For classification into T. gondii negative and positive subgroups, subjects with not detectable IgG antibody levels (n ¼ 36; serum level ¼ 0 UI/mL) were defined as negative, while those subjects with the highest concentration of IgG antibodies (n ¼ 36; mean serum level 152.1 UI/mL; range 54e510 UI/mL) were defined as positive (Fig. 1). The negative and positive subgroups did not differ significantly in gender distribution (according to a c2 test), or in age or level of education (according to 2way analyses of variance [ANOVAs] with between-subject factors group and gender; Table 1). Except for a measure of attentional endurance (assessed by the d2 test; Brickenkamp, 1994), ANOVAs applied to assess the neuropsychological characteristics of the participants did not indicate the significance between-group differences (all p > 0.05; Table 1) in depression (assessed by Becks Depression Inventory; Beck et al., 1961), cognitive failures (assessed by the Cognitive Failures Questionnaire; Broadbent et al., 1982), general cognitive status (assessed by the Mini Mental State Examination; Folstein et al., 1975), visual attention and task switching (assessed by the Trail Making Test; Reitan, 1958), spatial representation (assessed by a mental rotation task; Kersting et al., 2008), or crystalline intelligence (assessed by the Multiple choice Word Test, MWT-B; Lehrl, 1995). Nor there were any significant interactions of group and gender. All participants were informed about the scope of the study and gave written informed consent before any study protocol was commenced. However, the result of the immunoassay on T. gondii specific IgG antibodies was unknown to the participants of the study and to the operators who performed the cognitive testing, as the identification of T. gondii in the participants was conducted after the cognitive testing was finished. All participants gave written informed consent before any study protocol was commenced. They received a payment for their participation. The study conformed to the Code of Ethics of the World Medical Association (Declaration of Helsinki) and was approved by the Institutional Review Board. 2.2. Stimuli, task, and procedure Auditory stimuli were generated digitally using CoolEdit 2000 (Syntrillium Software Co, Phoenix, AZ, USA), and were presented binaurally using stereo headphones (AKG, K271 Studio) at the
A total of 131 healthy volunteers (mean age 70.3 years; range 63e88 years; 87 women) took part in the study. The participants were recruited through a number of newspaper advertisements and flyers distributed in the city of Dortmund (Germany). All data were gathered as part of a training study with a pre- and a postmeasure (for details: Gajewski and Falkenstein, 2012), with only the pre-measure data being reported here. The data of 7 participants were excluded from further analyses because of poor quality of the electroencephalography (EEG) and electro-oculography (EOG) data: 4 data sets showed high alpha activity, and in 3 data sets EOG channels were missing so that ocular artifacts correction was not possible. Identification of Toxoplasma-negative and -positive subjects without any clinical symptoms of acute toxoplasmosis was performed according to the following procedure: venous blood of all individuals was sampled and tested for T. gondii specific IgG antibodies. The analyses were performed in a certified local clinical
Anti-Toxoplasma IgG level [UI/ml]
2.1. Participants
600 male female
500 400 300 200 100 0 1
5
10
15
20
25
30
35
Subject Fig. 1. Individual anti-Toxoplasma IgG concentration of each serum positive participant, shown separately for male and female subjects.
C. Beste et al. / Neurobiology of Aging 35 (2014) 1037e1044
1039
Table 1 Sample characteristics and results of the sociodemographical and neuropsychological assessment for the IgG negative and IgG positive groups, shown separately for male and female subjects Gender
T. gondii gender
Male
Female
Male
Female
df
F
F
F
n ¼ 11 68.7 (1.1) 2.4 (0.3) 4.7 (0.8) 28.9 (3.7)
n ¼ 25 70.2 (0.7) 2.6 (0.4) 6.3 (1.2) 27.6 (2.5)
n ¼ 12 70.2 (1.0) 2,7 (0.3) 5.9 (0.8) 27.7 (3.7)
n ¼ 24 70.1(0.7) 3.0 (0.4) 5.0 (1.1) 31.3 (2.5)
72 71 72 71
0.46 0.88 0.01 0.16
0.74 0.79 0.12 0.14
0.74 0.02 1.56 0.64
383.2 (22.5) 20.9 (5.3) 2.1 (1.9)
405.5 (14.9) 24.0 (3.5) 3.0 (1.3)
378.3 (22.5) 20.0 (5.3) 3.6 (1.9)
398.7 (16.3) 20.8 (3.8) 9.0 (1.4)
68 68 68
0.07 0.20 5.10a
1.23 0.19 3.56
0.01 0.06 1,73
7.8 (1.0) 6.8 (0.9) 28.6 (0.3)
5.8 (0.7) 6.0 (0.6) 28.6 (0.5)
7.4 (1.0) 7.0 (0.9) 28.4 (0.3)
5.6 (0.7) 4.6 (0.6) 29.1 (0.5)
71 66 72
0.16 0.58 0.09
4.82a 4.45a 0.60
0.02 0.99 1.02
30.5 (0.9) 115.1 (3.4)
31.1 (0.9) 117.0 (2.3)
32.4 (0.9) 120.8 (3.4)
31.3 (0.6) 115.6 (2.3)
71 71
1.68 0.57
0.10 0.33
1.15 1.48
38.0 (4.0) 103.6 (11.7)
39.2 (2.5) 91.0 (7.4)
37.8 (2.6) 95.9 (7.5)
70 70
0.20 0.01
0.16 0.51
0.01 0.36
IgG negative
Number Age (y) Mean level of educationa BDI CFQa total score D2a Total number of symbols Number omitted symbols Number confused symbols Mental rotationa Total number Number correct MMSE MWT-Ba Number total IQ TMTa TMT-A TMT-B
IgG positive
36.4 (3.8) 97.1 (11.1)
T. gondii
Key: BDI, Beck Depression Inventory; CFQ, Cognitive Failures Questionnaire; D2, Test of Attention; Mean Level of Education: No degree (1) Primary; (2) Secondary general; (3) Intermediate secondary; (4) Gymnasium; MMSE, Mini Mental State Examination; MWT-B, multiple-choice word test, test of premorbid intelligence; T. gondii, Toxoplasma gondii; TMT, Trail Making Test. a Reduced number of participants. Significance level was set at p < 0.05.
intensity of 70 dB(A). They consisted of sine waves composed of base frequencies of either 500 Hz, 1000 Hz, or 2000 Hz. The stimuli were short (200 ms) and long (400 ms) tones (both including 5 ms rise and 5 ms fall times) presented equiprobably. Eighty percentages of these long and short tones were frequent standard stimuli (1000 Hz), and 20% were rare deviant stimuli (either 500 Hz or 2000 Hz, each 10%). The sequence of standard and deviant stimuli was pseudo-randomized. During testing, the participants sat on a comfortable chair in a dimly lit and quite room. A 2-alternative forced-choice duration discrimination task was used, in which the participants had to press 1 response button for short and the other for long tones irrespective of the pitch of the tone. The response buttons were held in the subject’s hands. The duration-hand contingency was counterbalanced between participants. Participants were instructed to respond in a fast but accurate manner. To avoid EEG alpha-activity and wandering eye-movements during the recordings, participants were instructed to keep their eyes open and to focus on a visual fixation point presented on a monitor placed in front of them. No feedback was given to the participants at any time during the experiment. To secure that the participants were able to reliably distinguish the tone pitches of the frequent and deviant stimuli, samples of the tones were presented and the participants were asked whether they hear the sounds, and whether they perceive the differences in pitch. All participants performed this task without any problems. Then, the participants carried out a short training until the task was familiar. Finally, all participants completed 2 test blocks interrupted by a rest break. A test block consisted of 120 trials (48 short and 48 long standard tones and 12 short and 12 long deviant tones). The stimulus onset asynchrony was 1400 ms. The timing of the stimuli and the recording of the participants’ responses were controlled by custom-written software. Reaction times (RTs) were measured by a high-resolution timer interface connected with the external response buttons. 2.3. Data recording The continuous EEG (amplifier bandpass 0.01e140 Hz) was sampled at 2048 Hz using 32 Ag/AgCl electrodes mounted on an
elastic cap according to the extended 10e20 system. The montage included 8 midline sites and 12 sites on each hemisphere. Horizontal and vertical eye positions were recorded by EOG using 4 electrodes positioned around both eyes. The ground electrode was placed on the center of the forehead, just above the nasion. Two additional electrodes were placed on the left and right mastoids (M1 and M2). Electrode impedance was kept below 10 kU. The raw data were offline downscaled to a sampling rate of 1000 Hz, bandpass filtered (cut-off frequencies 0.05 and 17 Hz), re-referenced to linked mastoids, and segmented into 1300-ms stimulus-locked epochs covering the period from 100 to 1200 ms relative to tone onset, using the BrainVision Analyzer software (version 1.05; Brain Products, Munich, Germany). The data were corrected for ocular artifacts using the Gratton and Coles procedure (Gratton et al., 1983). Individual epochs exceeding a maximum-minimum difference of 300 mV were excluded from further analysis (automatic artifact rejection as implemented in the BrainVision Analyzer software). The remaining epochs were baseline corrected with reference to a 100-ms prestimulus window, and averaged for each participant, separately for epochs with the deviant tones (averaged across the 500-Hz and 2000-Hz stimuli) and the standard tones. Trials with short and long tones were pooled, and averaged across the 2 test blocks to improve the signal-to-noise ratio of the EEG signal. Finally, difference waves were calculated (deviant minus standard) to analyze the deviance-related MMN, P3a, and RON components. 2.4. Data analysis Behavioral and ERP data were analyzed for standard and deviant tones. RT was defined as the time between the offset of the 200-ms tone and the push of a response button. Individual RTs of less than 100 ms and longer than 1200 ms, as well as error trials were excluded from further analysis. Rates of correct responses and mean RTs were subjected to 3-way ANOVAs with between-subject factors group (IgG negative vs. IgG positive) and gender (male vs. female), and within-subject factor stimulus (deviant vs. standard tones). In addition, the deviance-related distraction effect was defined as the percentage change in discrimination accuracy and
1040
C. Beste et al. / Neurobiology of Aging 35 (2014) 1037e1044
speed. It corresponds to (deviant standard tones)/standard tones 100, with deviant tones representing the correct responses and RTs to deviant tones and standard tones representing correct responses and RTs to standard tones. The ERP analysis was restricted to midline electrodes (Fz, FCz, Cz, and Pz) chosen to be commensurate with previous knowledge of the topographical scalp distribution of specific ERPs (review: Barrett et al., 1987; Näätänen and Picton, 1987; Polich, 2007), indicating that the N1, MMN, P3a, RON typically peak over frontocentral areas (FCz), the P2 over central areas (Cz), and the P3b over parietal areas (Pz) of the scalp. Peak amplitudes and latencies of these components were defined as their local maximum positivity or negativity within a particular latency window (N1 at FCz: 50e150 ms; MMN at FCz: 100e200 ms; P2 at Cz: 120e220 ms; P3a at FCz: 225e400 ms; P3b at Pz: 400e700 ms; RON at FCz: 400e700
3.1. Behavioral data IgG negative and positive participants did not differ significantly in the rate of correct responses, while both groups produced fewer correct responses to deviant tones than standard tones (Fig. 2A). The
100 95 90 85 80 75 70 65 0 Standard Deviant Tones
female Correct Responses [%]
male
B Response Times [ms]
3. Results
100 95 90 85 80 75 70 65 0 Standard Deviant Tones
male 550 525 500 475 450 425 400 375
female Response Times [ms]
Correct Responses [%]
A
ms after tone onset). The amplitudes and latencies of these components were subjected to 2-way ANOVAs with between-subject factors group and gender. Levene’s test was used to assess the homogeneity of variance, and the degrees of freedom were adjusted if variances were unequal. Effect sizes were computed to provide a more accurate interpretation of the practical significance of the findings, using the partial eta-squared coefficient.
0
550 525 500 475 450 425 400 375 0 Standard Deviant Tones
Standard Deviant Tones
C
D Change in Response Time [%]
Change [%]
15 12 9 6 3 0 Correct Responses
Response Times
IgG negative IgG positive
50 40 30 20 10 0 -10
r = 0.38 p < 0.05
100 200 300 400 500 Toxoplasma Toxoplasma IgGSerum antibody Concentration Serum Concentration [UI/ml]
0
Fig. 2. (A) Rates of correct responses and (B) response times for IgG serum negative and positive participants, shown separately for the frequent standard tones and the rare deviant tones, and for male and female participants. (C) Deviance-related percentage changes (deviant tones relative to standard tones) for IgG serum negative and positive participants (averaged across males and females), shown for the frequent standard tones and the rare deviant tones. Error bars indicate standard errors across participants (N ¼ 36). (D) Percentage change in response times as function of anti-Toxoplasma IgG concentrations for each serum positive participants (averaged across males and females) with linear regression line.
C. Beste et al. / Neurobiology of Aging 35 (2014) 1037e1044
ANOVA indicated a main effect of stimulus (F [1,68] ¼ 40.35; p < 0.001; partial ɳ2 ¼ 0.37), but no main effect of group (F [1,68] ¼ 0.14; p > 0.05; partial ɳ2 ¼ 0.00) or stimulus group interaction (F [1,68] ¼ 0.01; p > 0.05; partial ɳ2 ¼ 0.00). There were no interactions of group and gender (F [1,68] ¼ 0.24) or stimulus, group, and gender (F [1,68] ¼ 0.59; both p > 0.05; both partial ɳ2 < 0.01), while a main effect of gender (F [1,68] ¼ 6.42; p < 0.05; partial ɳ2 ¼ 0.09) indicated less correct responses of female than of male participants. RTs to deviant tones were significantly increased, relative to standard tones (Fig. 2B), as indicated by a main effect of stimulus (F [1,68] ¼ 61.68; p < 0.001; partial ɳ2 ¼ 0.48). Most importantly, while both groups did not differ in RTs per second, the deviance-related increase in RTs was more pronounced in the IgG positive, than IgG negative, group. Thus, there was a significant stimulus group interaction (F [1,68] ¼ 5.46; p < 0.05; partial ɳ2 ¼ 0.07), but no main effect of group (F [1,68] ¼ 1.63; p > 0.05; partial ɳ2 ¼ 0.02). The ANOVA also revealed a significant group gender interaction (F [1,68] ¼ 5.44; p < 0.05; partial ɳ2 ¼ 0.07): In the male group, RTs were larger in IgG positive, than IgG negative, participants (t [21] ¼ 2.87; p < 0.01), while RTs did not differ between IgG positive and IgG negative participant in the female group (t [21] ¼ 0.86; p > 0.05). There was no significant interaction of stimulus and gender (F [1,68] ¼ 0.85) and no significant main effect of gender (F [1,68] ¼ 0.38; both p > 0.05; both partial ɳ2 < 0.02). Also, there was no significant interaction of stimulus, group, and gender (F [1,68] ¼ 0.15, p > 0.05; partial ɳ2 < 0.01), suggesting that the more pronounced deviance-related increase in RTs in the IgG positive, than IgG negative, group did not depend on gender. Thus, taken male and female subjects together, it appeared that the IgG positive and IgG negative groups did not differ in the deviance-related decrease in correct responses (Fig. 2C; F [1,68] ¼ 0.04; p > 0.05; partial ɳ2 ¼ 0.00), whereas IgG positive participants showed a stronger increase in RTs than their IgG negative counterparts (F [1,70] ¼ 4.75; p < 0.05; partial ɳ2 ¼ 0.06). In addition to this between-group difference, there was a positive correlation of individual anti-Toxoplasma IgG concentrations and RT increase within the IgG positive group (Fig. 2D), indicating that higher anti-Toxoplasma IgG concentrations were associated with delayed duration discrimination of deviant tones. 3.2. ERPs Standard tones produced a typical fronto-central N1-P2 complex peaking at 95 ms and 183 ms, respectively, and a pronounced parietal P3b peaking at about 600 ms (Fig. 3A). In contrast, deviant tones produced, beside a fronto-central N1 and a parietal P3b, a strong fronto-central positivity at about 300 ms after tone onset. The difference waveforms (deviant minus standard tones, Fig. 3B) indicated a fronto-central MMN (peaking at 138 ms), P3a (peaking at 304 ms), and RON (peaking at 521 ms after tone onset). The ERPs to standard tones (N1, P2, P3b) did not differ significantly between groups, neither in amplitudes nor latencies (Table 2), while amplitudes of P2 and P3b were larger in female than in male participants. Also, the N1 response to deviant tones did not differ between groups. However, the analysis of the difference waveforms revealed significantly delayed P3a and RON responses in IgG positive, relative to IgG negative, participants. No significant differences occurred in P3a and RON amplitudes, or in MMN amplitudes or latencies. Also, there were no group gender interactions, neither for ERPs to standard tones, nor for the difference waveforms. In sum, while the 2 groups did not differ in the processing of standard tones, the deviance-related fronto-central positivity P3a and RON components were delayed in the IgG positive group. An additional correlation analysis did not indicate significant correlations of ERPs and individual anti-Toxoplasma IgG concentrations
1041
within the IgG positive group (all p > 0.05), except for a slight positive correlation of IgG concentrations and P3a amplitude (p ¼ 0.054; Bonferroni-corrected value). 4. Discussion In the present study we examined the role of latent T. gondii infection as a modulator for goal-directed behavior in healthy elderly individuals. The results show that latent T. gondii infection compromises goal-directed behavior. Using an auditory distraction paradigm we show that elderly individuals with positive IgG Toxoplasma serum concentrations revealed slower RTs, when confronted with deviant stimuli. No effects of T. gondii infection were evident on standard trials. The effects at the behavioral level were predictable on the basis of individual anti-Toxoplasma IgG concentrations. Higher concentrations were related to longer reaction times on deviant trials. This suggests that declines in goal-directed behavior under auditory distraction are directly related to the effects of T. gondii. The neurophysiological data suggest that these behavioral deficits emerge as a consequence of specific effects of T. gondii on a subset of cognitive processes mediating goal-directed behavior. The ERP data show that T. gondii did not affect amplitude and latency of the N1 and P2, as well as the mismatch negativity MMN. This suggests that attentional selection mechanisms, as reflected by the N1 and P2 (e.g., Herrmann and Knight, 2001; Potts, 2004) are not modulated and do therefore not contribute to the observed slowing in RTs on deviant trials. Similarly, the results suggest that auditory sensory memory processes (reflected by the MMN, e.g., Näätänen et al., 2012) are not modulated by T. gondii. This suggests that T. gondii does not affect the ability of pre-attentive processes detecting differences in incoming sensory information. However, for the P3a as well as for the RON, shifts in latency were evident in T. gondii IgG serum positive elderly individuals. No effects were evident for the amplitudes. The P3a has been suggested to reflect processes of attentional allocation (Hölig and Berti, 2010; Polich, 2007). In deviant trials the P3a may reflect a mechanism of attentional disengagement (Berti, 2008). In this sense, the P3a reflects attentional allocation processes and shifts or switches in attention (e.g.,Escera and Corral, 2007; Escera et al., 2000; Schröger, 1996). The longer latency of the P3a in IgG serum positive elderly individuals suggests that these involuntary processes take longer to become fully effective. As a consequence of this longer latency to activate additional processing resources under auditory distraction, behavioral performance, and goal-directed behavior become deficient. However, the results show that also the RON revealed a prolonged latency in IgG serum positive elderly individuals. The RON has been suggested to reflect the reorientation of attention after distraction (e.g., Schröger et al., 2000). Yet, it is likely that the prolonged RON latency reflects a simple aftereffect of the prolonged P3a latency. The P3a precedes the RON. A shift in latency of the P3a therefore most likely affects the RON latency. Corroborating this interpretation that the RON latency shift does not reflect a “real” effect of different Toxoplasma IgG levels in elderly individuals, the behavioral data on standard trials were not different between the groups. A latency shift in RON would imply that re-orientation processes toward standard trials are deficient. This would most likely entail longer reaction times on standard trials, too, as found in a number of studies (see Flegr, 2013 for overview). It may be regarded counterintuitive why T. gondii, is known to increase dopaminergic turnover, confers negative effects on goaldirected behavior. However, network characteristics in prefrontal cortices, which are important for goal-directed behavior, strongly vary depending on the relative influence of D1 versus D2-receptor
1042
C. Beste et al. / Neurobiology of Aging 35 (2014) 1037e1044
A
B
ERPs
Deviant-Standard Differences
Fz
Fz
P2
FCz
P3a
FCz
MMN
RON
N1 Cz
Cz
P3b
Pz
Pz
2 µV
+ 200 ms
Standards, IgG negative Deviants, IgG negative Standards, IgG positive Deviants, IgG positive
IgG negative IgG positive
Fig. 3. Grand average ERPs of the frequent standard tones and the rare deviant tones (A), and difference waves (B, deviant minus standard tones) at Fz, FCz, Cz, and Pz, shown for IgG serum negative and positive participants (averaged across males and females). The vertical lines reflect the onset of the tone stimulus. ERP components (N1, P2, P3a, P3b, MMN, and RON) are marked at the waveform of maximal amplitude. Abbreviations: ERP, event-related potential; MMN, mismatch negativity; RON, re-orienting negativity.
related neural transmission (Durstewitz and Seamans, 2008; Seamans and Yang, 2004). A highly active dopamine D2 system has been shown to allow the establishment of multiple representations in prefrontal cortical networks and working memory, that is the processing capacity of the network is increased. This state is more responsive and flexible, but also more interference-prone compared with a network state dominated by high dopamine D1 receptor turnover (Durstewitz and Seamans, 2008). The task
applied specifically examines the robustness of representations against interference. It has been shown previously that haloperidol, a D2-receptor antagonist is able to suppress effects of T. gondii infection (Webster et al., 2006; Gajewski et al., submitted). It is therefore likely that especially dopaminergic neural transmission mediated via D2 receptors in enhanced in latent T. gondii infection. Given this, it is plausible that especially the distracting deviant trials show effects of latent T. gondii infection. In a previous study,
C. Beste et al. / Neurobiology of Aging 35 (2014) 1037e1044
1043
Table 2 Mean amplitudes (Amp. in mV) and latencies (Lat. in ms) and standard error of means of the event-related potentials of IgG serum negative and positive participants for standard and deviant tones, shown separately for males and females, with F statistics and effect sizes. Mismatch negativity (MMN), P3a, and re-orienting negativity (RON) refer to the difference event-related potentials (deviant minus standard tones) IgG negative Male Standard tones N1 Amp. P2 Amp. P3b Amp. N1 Lat. P2 Lat P3b Lat. Deviant tones N1 Amp. MMN Amp. P3a Amp. RON Amp. N1 Lat. MMN Lat. P3a Lat. RON Lat.
IgG positive Female
Male
T. gondii Female
F1,
72
T. gondii gender
Gender ɳ2p
F1,
72
ɳ2p
F1,
72
ɳ2p
4.2 1.8 3.9 94.4 173.2 607.5
(0.7) (0.7) (0.7) (2.3) (6.6) (14.1)
4.3 2.7 4.8 94.0 173.9 622.9
(0.5) (0.4) (0.5) (1.5) (4.4) (9.3)
3.9 1.2 2.8 94.3 174.4 611.3
(0.7) (0.6) (0.7) (2.3) (6.3) (13.5)
3.9 3.2 4.5 91.2 176.5 605.9
(0.5) (0.4) (0.5) (1.6) (4.5) (9.2)
0.33 0.07 1.49 0.57 0.11 0.32
0.01 0.00 0.02 0.01 0.01 0.01
0.01 6.89* 4.96* 0.82 0.06 0.18
0.00 0.09 0.07 0.01 0.01 0.01
0.01 0.94 0.59 0.54 0.02 0.78
0.00 0.01 0.01 0.01 0.00 0.01
4.5 1.5 3.7 2.4 98.2 137.2 294.6 481.5
(0.8) (0.6) (0.7) (0.7) (3.7) (8.5) (11.4) (19.2)
5.3 2.3 4.6 2.8 96.7 143.0 289.2 539.8
(0.5) (0.4) (0.4) (0.5) (2.5) (5.7) (7.6) (12.8)
4.5 1.4 3.3 2.8 96.8 134.2 316.4 560.2
(0.8) (0.6) (0.6) (0.5) (3.5) (8.2) (10.9) (18.1)
4.7 2.3 4.0 2.5 97.0 140.3 323.0 564.1
(0.6) (0.4) (0.4) (0.5) (2.5) (5.8) (7.7) (13.0)
0.20 0.00 0.78 0.01 0.03 0.16 8.48** 10.19**
0.01 0.00 0.01 0.00 0.00 0.01 0.11 0.13
0.41 2.41 2.46 0.04 0.05 0.70 0.01 3.73
0.01 0.03 0.04 0.01 0.01 0.01 0.00 0.05
0.16 0.01 0.05 0.35 0.07 0.01 0.39 2.85
0.01 0.00 0.01 0.01 0.00 0.00 0.01 0.04
Key: MMN, mismatch negativity; RON, re-orienting negativity; T. gondii, Toxoplasma gondii. * p < 0.05, ** p < 0.01.
we found that infected individuals showed a clear impairment in different memory functions, while executive functions operating with visual stimuli in the Stroop task (inhibition) and the trails B task (shifting) were not affected. However, attention-related functions with auditory stimuli were not examined in that study (Gajewski et al., 2014). With respect to the interpretation of the results in relation to the dopaminergic system it is important to note that even in the stage of latent T. gondii infection, the dopamine system is affected. Subjects tested are not in the stage of acute of infection, but in the stage of latent infection. This stage (cysts [bradyzoites] stage) is indicated by the positive IgG marker and these cysts persist lifelong in host tissues (e.g., Robert-Gangneux and Darde, 2012). Importantly, Prandovszky et al. (2011) showed that in exactly this “cyst stage” (i.e., where no acute T. gondii infection is evident, but a latent T. gondii infection is evident) in chronically infected mice brains, parasite cysts contained high levels of dopamine based on staining with a commercial antibody specific to dopamine (for review: McConkey et al., 2013). This study clearly shows that the interaction of T. gondii with the dopamine system is not limited to the stage of acute infection, but rather persists in the stage of chronic infection. In their in vitro study Prandovszky et al. (2011) showed that “dopamine release increased in infected cultures in a dosedependent manner with the number of parasites in the culture correlating with the amount of dopamine released” (p. 5). However, it has to be noted that 1 animal study did not account for T. gondii induced changes in the dopamine system (Goodwin et al., 2012). Goodwin et al. (2012) did also not account for behavioral changes, even though most results in the field clearly demonstrate such changes. Hence, the mechanism that dopamine may be the critical factor influenced by T. gondii has to be treated with some caution. However, with respect to the possible neuronal mechanism it has further to be noted that an effect of T. gondii in the behavioral data (i.e., larger RTs in IgG positive, than IgG negative, participants) was evident in men, but not in women, which corroborates data by Flegr et al. (2008). Flegr et al. (2008) noted that this may be because of the hormonal status relating to varying levels in different steroid hormones. This does not foreclose the previously mentioned interpretation suggesting that the dopamine system plays an important role, because steorid hormones are well-known to modulate dopaminergic neural transmission (for review: Zheng et al., 2009).
In summary, the study shows that latent T. gondii infection modulates goal-directed behavior in otherwise healthy elderly individuals. The individual IgG antibody serum concentration was predictive for behavioral performance in goal-directed behavior. The effects of T. gondii are restricted to a subset of cognitive processes mediating goal-directed behavior. In particular processes related to attentional allocation of processing resources. Other processes like bottom-up attentional processes or sensory memory processes are not affected. This dissociated pattern of results may emerge as a consequence of a differential relevance of the dopaminergic systems for these cognitive subprocesses. The results show that latent T. gondii infection is an important neurobiological modulator that needs to be taken into account when examining cognitive functions in elderly individuals. Disclosure statement All authors disclose no actual or potential conflicts of interest including any financial, personal, or other relationships with other people or organizations that could inappropriately influence (bias) their work. Acknowledgements We thank the participants, Ludger Blanke, Pia Deltenre, Brita Rietdorf, Claudia Wipking, Kirsten Liesenhoff-Henze, Marion Page, and Claudia Schulte-Dahmann for excellent technical and organizational assistance, and Dr Meinolf Blaszkewicz for his support. This work was funded by a grant from the German Insurance Association (GDV, Gesamtverband der Deutschen Versicherungswirtschaft) to P.G. and M.F., and by a Grant from the Deutsche Forschungsgemeinschaft (DFG) to C.B. (BE 4045/10-1) and S.G. (GE 1920/3-1). References Bäckman, L., Lindenberger, U., Li, S.C., Nyberg, L., 2010. Linking cognitive aging to alterations in dopamine neurotransmitter functioning: recent data and future avenues. Neurosci. Biobehav. Rev. 34, 670e677. Barrett, G., Neshige, R., Shibasaki, H., 1987. Human auditory and somatosensory event-related potentials: effects of response condition and age. Electroencephalogr. Clin. Neurophysiol. 66, 409e419. Beck, A.T., Ward, C.H., Mendelson, M., Mock, J., Erbaugh, J., 1961. An inventory for measuring depression. Arch. Gen. Psychiatry 4, 561e571.
1044
C. Beste et al. / Neurobiology of Aging 35 (2014) 1037e1044
Berti, S., 2008. Cognitive control after distraction: event-related brain potentials (ERPs) dissociate between different processes of attentional allocation. Psychophysiology 45, 608e620. Beste, C., Stock, A.K., Ness, V., Epplen, J.T., Arning, L., 2012. Differential effects of ADORA2A gene variations in pre-attentive visual sensory memory subprocesses. Eur. Neuropsychopharmacol. 22, 555e561. Beste, C., Schneider, D., Epplen, J.T., Arning, L., 2011. The functional BDNF Val66Met polymorphism affects functions of pre-attentive visual sensory memory processes. Neuropharmacology 60, 467e471. Beste, C., Domschke, K., Kolev, V., Yordanova, J., Baffa, A., Falkenstein, M., Konrad, C., 2009. Functional 5-HT1a receptor polymorphism selectively modulates errorspecific subprocesses of performance monitoring. Hum. Brain Mapp. 31, 621e630. Beste, C., Saft, C., Güntürkün, O., Falkenstein, M., 2008. Increased cognitive functioning in symptomatic Huntington’s disease as revealed by behavioral and event-related potential indices of auditory sensory memory and attention. J. Neurosci. 28, 11695e11702. Brickenkamp, R., 1994. Test d2, Aufmerksamkeits-belastungs-test, eighth ed. Hogrefe, Goettingen. Broadbent, D.E., Cooper, P.F., FitzGerald, P., Parkes, K.R., 1982. The cognitive failures questionnaire (CFQ) and its correlates. Br. J. Clin. Psychol. 21, 1e16. Buckner, R.L., 2004. Memory and executive function in aging and AD: multiple factors that cause decline and reserve factors that compensate. Neuron 30, 195e208. Durstewitz, D., Seamans, J.K., 2008. The dual-state theory of prefrontal cortex dopamine function with relevance to catechol-o-methyltransferase genotypes and schizophrenia. Biol. Psychiatry 64, 739e749. Escera, C., Alho, K., Schröger, E., Winkler, I., 2000. Involuntary attention and distractibility as evaluated with event-related brain potentials. Audiol. Neurootol. 5, 151e166. Escera, C., Corral, M.J., 2007. Role of mismatch negativity and novelty-P3 in involuntary auditory attention. J. Psychophysiol. 21, 251e264. Flegr, J., 2007. Effects of toxoplasma on human behavior. Schizophr. Bull. 33, 757e760. Flegr, J., Novotná, M., Lindová, J., Havlí cek, J., 2008. Neurophysiological effect of the Rh factor. Protective role of the RhD molecule against Toxoplasma-induced impairment of reaction times in women. Neuro. Endocrinol. Lett. 29, 475e481. ski, M., Deptu1a, A., Zalas-Wie˛ cek, P., Piskunowicz, M., Flegr, J., Guenter, W., Bielin ski, A., Gospodarek, E., Borkowska, A., 2012. Toxoplasma gondii Szwed, K., Bucin infection affects cognitive function e corrigendum. Folia Parasit. 59, 253e254. Flegr, J., 2013. Influence of latent Toxoplasma infection on human personality, physiology and morphology: pros and cons of the Toxoplasma-human model in studying the manipulation hypothesis. J. Exp. Biol. 216, 127e133. Fillenz, M., 1993. Short-term control of transmitter synthesis in central catecholaminergic neurones. Prog. Biophys. Mol. Biol. 60, 29e46. Folstein, M.F., Folstein, S.E., McHugh, P.R., 1975. “Mini-mental state”. A practical method for grading the cognitive state of patients for the clinician. J. Psychiatr. Res. 12, 189e198. Gajewski, P.D., Hengstler, J.G., Falkenstein, M., Golka, K., 2014. Toxoplasma gondii impairs memory in infected seniors. Brain Behav. Immun. 36, 193e199. Gajewski, P.D., Falkenstein, M., 2012. Training-induced improvement of response selection and error detection in aging assessed by task switching: effects of cognitive, physical, and relaxation training. Front. Hum. Neurosci. 6, 130. Gatkowska, J., Wieczorek, M., Dziadek, B., Dzitko, K., Dlugonska, H., 2012. Behavioral changes in mice caused by Toxoplasma gondii invasion of brain. Parasitol. Res. 111, 53e58. Gaskell, E.A., Smith, J.E., Pinney, J.W., Westhead, D.R., McConkey, G.A., 2009. A unique dual activity amino acid hydroxylase in Toxoplasma gondii. PLoS One 4, e4801. Getzmann, S., Gajewski, P.D., Hengstler, J.G., Falkenstein, M., Beste, C., 2013a. BDNF Val66Met polymorphism and goal-directed behaviour in healthy elderly e evidence from auditory distraction. NeuroImage 64, 290e298. Getzmann, S., Gajewski, P.D., Falkenstein, M., 2013b. Does age increase auditory distraction? Electrophysiological correlates of high and low performance in seniors. Neurobiol. Aging 34, 1952e1962. Goodwin, D., Hrubec, T.C., Klein, B.G., Strobl, J.S., Werre, S.R., Han, Q., Zajac, A.M., Lindsay, D.S., 2012. Congenital infection of mice with Toxoplasma gondii induces minimal change in behavior and no change in neurotransmitter concentrations. J. Parasitol. 98, 706e712. Gratton, G., Coles, M.G.H., Donchin, E., 1983. A new method for off-line removal of ocular artifact. Electroencephalogr. Clin. Neurophysiol. 55, 468e484. Herrmann, C.S., Knight, R.T., 2001. Mechanisms of human attention: event-related potentials and oscillations. Neurosci. Biobehav. Rev. 25, 465e476. Hoelig, C., Berti, S., 2010. To switch or not to switch: brain potential indices of attentional control after task-relevant and task-irrelevant changes of stimulus features. Brain Res. 1345, 164e174. Horváth, J., Czigler, I., Birkás, E., Winkler, I., Gervai, J., 2009. Age-related differences in distraction and reorientation in an auditory task. Neurobiol. Aging 30, 1157e1172. Javitt, D.C., Steinschneider, M., Schroeder, C.E., Arezzo, J.C., 1996. Role of cortical Nmethyl-D-aspartate receptors in auditory sensory memory and mismatch
negativity generation: implications for schizophrenia. Proc. Natl. Acad. Sci. U.S.A 93, 11962e11967. Kersting, M., Althoff, K., Jäger, A.O., 2008. WIT-2. Der Wilde-Intelligenztest. Verfahrenshinweise. Hogrefe, Göttingen. Kropotov, J.D., Alho, K., Näätänen, R., Ponomarev, V.A., Kropotova, O.V., Anichkov, A.D., Nechaev, V.B., 2000. Human auditory-cortex mechanisms of preattentive sound discrimination. Neurosci. Lett. 280, 87e90. Lehrl, S., 1995. Mehrfach-Wortwahl-Test (MWT). Medizinische Verlagsgesellschaft, Erlangen. McConkey, G.A., Martin, H.L., Bristow, G.C., Webster, J.P., 2013. Toxoplasma gondii infection and behaviour: location, location, location? J. Exp. Biol. 216, 113e119. Miman, O., Kusbeci, O.Y., Aktepe, O.C., Cetinkaya, Z., 2010. The probable relation between Toxoplasma gondii and Parkinson’s disease. Neurosci. Lett. 475, 129e131. Näätänen, R., Kujala, T., Escera, C., Baldeweg, T., Kreegipuu, K., Carlson, S., Ponton, C., 2012. The mismatch negativity (MMN)ea unique window to disturbed central auditory processing in ageing and different clinical conditions. Clin. Neurophysiol. 123, 424e458. Näätänen, R., Picton, T.W., 1987. The N1 wave of the human electric and magnetic response to sound: a review and an analysis of the component structure. Psychophysiology 24, 375e425. Nagy, A., Paroczy, Z., Norita, M., Benedek, G., 2005. Multisensory responses and receptive field properties of neurons in the substantia nigra and in the caudate nucleus. Eur. J. Neurosci. 22, 419e424. Nieoullon, A., 2002. Dopamine and the regulation of cognition and attention. Prog. Neurobiol. 67, 53e83. Polich, J., 2007. Updating P300: an integrative theory of P3a and P3b. Clin. Neurophysiol. 118, 2128e2148. Potts, G.F., 2004. An ERP index of task relevance evaluation of visual stimuli. Brain Cogn. 56, 5e13. Prandovszky, E., Gaskell, E., Martin, H., Dubey, J.P., Webster, J.P., McConkey, G.A., 2011. The neurotropic parasite Toxoplasma gondii increases dopamine metabolism. PLoS One 6, e23866. Reitan, R.M., 1958. Validity of the Trail Making Test as an indicator of organic brain damage. Percept. Mot. Skills 8, 271e276. Robert-Gangneux, F., Darde, M.L., 2012. Epidemiology of and diagnostic strategies for toxoplasmosis. Clin. Microbiol. Rev. 25, 264e296. Ruzzoli, M., Pirulli, C., Brignani, D., Maioli, C., Miniussi, C., 2012. Sensory memory during physiological aging indexed by mismatch negativity (MMN). Neurobiol. Aging 33, 625.e21e625.e30. Saft, C., Schüttke, A., Beste, C., Andrich, J., Heindel, W., Pfleiderer, B., 2008. fMRI reveals altered auditory processing in manifest and premanifest Huntington’s disease. Neuropsychologia 46, 1279e1289. Schröger, E., 1996. A neural mechanism for involuntary attention shifts to changes in auditory stimulation. J. Cogn. Neurosci. 8, 527e539. Schröger, E., Wolff, C., 1998. Attentional orienting and reorienting is indicated by human event-related brain potentials. Neuroreport 9, 3355e3358. Schröger, E., Giard, M.H., Wolff, C., 2000. Auditory distraction: event-related potential and behavioural indices. Clin. Neurophysiol. 111, 1450e1460. Seamans, J.K., Yang, C.R., 2004. The principal features and mechanisms of dopamine modulation in the prefrontal cortex. Prog. Neurobiol. 74, 1e58. Siemens Healthcare Diagnostics, 2010. Enzygnost Toxoplasmosis/IgG Edition September 2010. Tenter, A.M., Heckeroth, A.R., Weiss, L.M., 2000. Toxoplasma gondii: from animals to humans. Int. J. Parasitol. 30, 1217e1258. Turchi, J., Sarter, M., 2001. Bidirectional modulation of basal forebrain N-methyl-Daspartate receptor function differentially affects visual attention but not visual discrimination performance. Neuroscience 104, 407e417. Umbricht, D., Koller, R., Vollenweider, F.X., Schmid, L., 2002. Mismatch negativity predicts psychotic experiences induced by NMDA receptor antagonist in healthy volunteers. Biol. Psychiatry 51, 400e406. Webster, J.P., Lamberton, P.H., Donnelly, C.A., Torrey, E.F., 2006. Parasites as causative agents of human affective disorders? The impact of anti-psychotic, moodstabilizer and anti-parasite medication on Toxoplasma gondii’s ability to alter host behaviour. Proc. Biol. Sci. 273, 1023e1030. Webster, J.P., 2007. The effect of Toxoplasma gondii on animal behavior: playing cat and mouse. Schizophr. Bull. 33, 752e756. Webster, J.P., Kaushik, M., Bristow, G.C., McConkey, G.A., 2013. Toxoplasma gondii infection, from predation to schizophrenia: can animal behavior help us understand human behaviour? J. Exp. Biol. 216, 99e112. Willemssen, R., Falkenstein, M., Schwarz, M., Müller, T., Beste, C., 2011. Effects of aging, Parkinson’s disease, and dopaminergic medication on response selection and control. Neurobiol. Aging 32, 327e335. Zheng, P., 2009. Neuroactive steorif regulation of neurotransmitter release in the CNS: action, mechanism and possible significance. Prog. Neurobiol. 89, 134e152. Znamenskiy, P., Zador, A., 2013. Corticostriatal neurones in auditory cortex drive decisions during auditory discrimination. Nature 497, 482e486.