Effects of methylphenidate on olfaction and frontal and temporal brain oxygenation in children with ADHD

Journal of Psychiatric Research 45 (2011) 1463e1470

Contents lists available at ScienceDirect

Journal of Psychiatric Research journal homepage: www.elsevier.com/locate/psychires

Effects of methylphenidate on olfaction and frontal and temporal brain oxygenation in children with ADHD Martin Schecklmann a, b, c, *, Matthias Schaldecker b, Susanne Aucktor b, Julia Brast c, Katharina Kirchgäßner c, Andreas Mühlberger d, Andreas Warnke c, Manfred Gerlach c, Andreas J. Fallgatter b, e,1, Marcel Romanos c, f,1 a

Department of Psychiatry, Psychosomatics and Psychotherapy, University of Regensburg, Germany Department of Psychiatry, Psychosomatics and Psychotherapy, University Clinic of Würzburg, Germany Department of Child and Adolescent Psychiatry, Psychosomatics and Psychotherapy, University Clinic of Würzburg, Germany d Department of Psychology I, Biological Psychology, Clinical Psychology and Psychotherapy, University of Würzburg, Germany e Department of Psychiatry, Psychosomatics and Psychotherapy, University of Tübingen, Germany f Department of Child and Adolescent Psychiatry, Psychosomatics and Psychotherapy, University Clinic of Munich, Germany b c

a r t i c l e i n f o

a b s t r a c t

Article history: Received 19 January 2011 Received in revised form 23 May 2011 Accepted 30 May 2011

Objective: Olfaction and attention-deficit-/hyperactivity disorder (ADHD) are mediated by dopamine metabolism and fronto-temporal functioning converging in recent findings of increased olfactory sensitivity in children with ADHD modulated by methylphenidate (MPH) and altered frontal and temporal oxygenation in adults with ADHD. Method: We investigated olfactory sensitivity, discrimination, and identification (Sniffin’ Sticks) in 27 children and adolescents with ADHD under chronic MPH medication and after a wash-out period of at least 14 half-lives in balanced order and 22 controls comparable for handedness, age, and intelligence. In addition, inferior frontal and temporal oxygenation was measured by means of functional near-infrared spectroscopy (fNIRS) during the presentation of 2-phenylethanol. Group differences in regard to sex distribution were statistically controlled for by analysis of covariance. Results: Patients did not differ from controls in any olfactory domain under treatment with MPH. Cessation of medication led to a significant increase in olfactory discrimination. Controls displayed typical inferior frontal and temporal brain activity in response to passive olfactory stimulation, while brain oxygenation was diminished in the patient group when assessed without medication. Under medication ADHD patients showed a trend for a normalisation of brain activity in the temporal cortex. Conclusions: The here reported effects of MPH cessation on olfactory discrimination and frontal and temporal oxygenation along with previous findings of increased olfactory sensitivity in medication-naïve ADHD children and its normalisation under chronic MPH treatment lead to the conclusion that MPH exerts differential chronic effects vs. acute cessation effects on altered olfactory function in ADHD. These effects are most probably mediated by modulation of the dopaminergic system. Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction Attention-deficit-/hyperactivity disorder (ADHD) is associated with alterations in the dopaminergic system as indicated by genetic, imaging, neuropsychological, pharmacological and animal studies (Levy and Swanson, 2001; Polanczyk and Rohde, 2007; Sontag et al., 2008; Genro et al., 2010). Both structural and * Corresponding author. University of Regensburg, Department of Psychiatry, Psychosomatics and Psychotherapy, Universitätsstraße 84, 93053 Regensburg, Germany. Tel.: þ49 941 941 2054; fax: þ49 941 941 2025. E-mail address: [email protected] (M. Schecklmann). 1 Both authors contributed equally. 0022-3956/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpsychires.2011.05.011

functional changes implicate prefrontal, cerebellar, and striatal brain areas in the pathophysiology of ADHD (Schneider et al., 2006; Romanos et al., 2010). Although the main focus of neuroimaging and neuropsychological ADHD research lies on higher cognitive functions there is increasing evidence for disturbance of rather basal functions such as olfactory perception (Gansler et al., 1998; Murphy et al., 2001; Karsz et al., 2008; Romanos et al., 2008; Schecklmann et al., 2011). Olfaction is mediated by neurotransmitters such as dopamine (Halasz and Shepherd, 1983; Hsia et al., 1999) and processed in various cortical areas (especially in temporal and frontal cortex) largely circumventing the thalamic relay (Savic, 2002; Albrecht and

1464

M. Schecklmann et al. / Journal of Psychiatric Research 45 (2011) 1463e1470

Wiesmann, 2006). In the olfactory bulbs odour information is synaptically transmitted from primary to secondary olfactory neurons. At this early stage dopaminergic interneurons modulate odour detection and discrimination via D2 receptors by contrast enhancement of incoming odour information (Halasz and Shepherd, 1983; Hsia et al., 1999; Cleland and Sethupathy, 2006). Previous studies on olfaction in ADHD reported alterations in olfactory identification; however, those studies are of limited informative value due to the sole investigation of identification (Gansler et al., 1998; Murphy et al., 2001; Karsz et al., 2008), lack of control for IQ (Karsz et al., 2008) and lack of a control group (Gansler et al., 1998). To overcome these shortcomings, we previously conducted investigations in children and adults with ADHD and controls carefully matched for age, gender and IQ (Romanos et al., 2008; Schecklmann et al., 2011). By using the validated olfactory testing instrument Sniffin’ Sticks (Burghart Instruments, Germany) we found no differences for identification and discrimination, but superior olfactory sensitivity in those children with ADHD who did not receive chronic pharmacotherapy with methylphenidate (MPH). In contrast, olfactory sensitivity of children with ADHD receiving constant stimulant medication did not differ from controls suggesting that pharmacological treatment normalizes increased sensitivity (Romanos et al., 2008). Olfactory stimulation by passive presentation of odours in healthy subjects has been shown to induce oxygenation changes in fronto‑polar, orbito-frontal, and temporal cortex (Fladby et al., 2004; Ishimaru et al., 2004a; Ishimaru et al., 2004b; Harada et al., 2006). In our adult ADHD sample we found diminished inferior frontal and temporal oxygenation during olfactory stimulation measured by the optical method functional near-infrared spectroscopy (fNIRS) (Schecklmann et al., 2011). These findings support the notion of altered olfactory central processing in ADHD. In conclusion, both olfactory functioning and pathophysiological pathways in ADHD are considered to involve dopamine metabolism

and frontal and temporal cortex functioning. These considerations converged in recent findings of increased olfactory sensitivity in children with ADHD without standard intake of MPH and altered frontal and temporal oxygenation patterns in adults with ADHD. Thus, we here aimed to further investigate the effects of MPH treatment on olfactory function in a within-subject design. We investigated children with chronic medication during intake of MPH and after short-term cessation of MPH by means of the Sniffin’ Sticks and fNIRS in a balanced order. Based on previous findings we expected normalized olfactory sensitivity and brain activity of the inferior frontal and temporal cortex in children with ADHD during chronic treatment of MPH and we hypothesized that cessation of MPH will reinstate increased sensitivity and diminished brain activity. 2. Method 2.1. Subjects For all details and group statistics please refer to Table 1. A priori we had to exclude four patients (two with combined and two with inattentive subtype) and one control due to technical reasons (participating in only one session or low fNIRS data quality) from the study. We examined a total of 49 children aged 10 to 16 years (27 patients with ADHD and 22 healthy controls). Patients were recruited and diagnosed in the framework of a nationally funded research project (Deutsche Forschungsgemeinschaft, KFO 125) ensuring a qualitatively high diagnostic procedure. All ADHD patients were evaluated by a semi-structured interview (KiddieSads - Present and Lifetime Version, German Version) (Kaufman et al., 1997) carried out by experienced physicians in the Department of Child and Adolescent Psychiatry, Psychosomatics, and Psychotherapy of the University Hospital of Wuerzburg. All patients met criteria for ADHD according to the DSM-IV classification system (314.00 and 314.01). 22 patients fulfilled criteria for the

Table 1 Sample characteristics (mean  sd). Healthy control children (n ¼ 22)

Patient children (n ¼ 27)

Statistics for group comparisons

With/without MPH (n ¼ 13)

Without/with MPH (n ¼ 14)

Statistics for group comparisons

Age (months)

149  19

152  17

157  17

148  16

Intelligence (IQ)

112  13 (n ¼ 21)

109  12 (n ¼ 26)

106  13

112  11 (n ¼ 13)

Handedness (Edinburgh scale) Gender (female/male)

84  14 (n ¼ 21)

84  18

88  14

81  22

14/8

7/20

3/10

4/10

Internal problem behavior (CBCL sum) External problem behavior (CBCL sum) Attention (ADHS-DC score) Hyperactivity (ADHS-DC score) Impulsivity (ADHS-DC score) Impulsivity (IVE sum)

3.7  4.0

8.7  7.5

9.5  7.2

7.9  8.0

3.5  4.3

15.4  8.3

16.7  7.3

14.2  9.2

0.3  0.3

2.0  0.8

2.3  0.6

1.7  0.9

0.1  0.1

0.8  0.8

0.7  0.7

0.9  0.8

0.2  0.3

1.3  0.9

1.3  0.8

1.3  1.0

5.6  3.8 (n ¼ 21)

9.0  3.5

9.1  3.1

9.0  3.9

Depressivity (DIKJ sum)

7.2  5.7 (n ¼ 21)

10.4  6.3

11.3  6.7

9.6  6.1

Constant medication intake (months) Wash-out period without (days) Medication intake with (minutes) Comorbidity (yes/no)

e

e

t ¼ 0.8; df ¼ 47; p ¼ 0.451 t ¼ 0.9; df ¼ 45; p ¼ 0.388 t ¼ 0.1; df ¼ 46; p ¼ 0.966 c2 ¼ 7.0; df ¼ 1; p ¼ 0.008* t ¼ 2.8; df ¼ 47; p ¼ 0.007* t ¼ 6.1; df ¼ 47; p < 0.001* t ¼ 8.9; df ¼ 47; p < 0.001* t ¼ 4.6; df ¼ 47; p < 0.001* t ¼ 5.4; df ¼ 47; p < 0.001* t ¼ 3.3; df ¼ 46; p < 0.002* t ¼ 1.8; df ¼ 46; p ¼ 0.074 e

39.5  17.1

30.6  18.6

e

e

e

2.0  0.4 (n ¼ 12)

11.0  11.9

e

e

e

155.8  109.6

129.1  104.8

e

e

e

6/7

6/8

t ¼ 1.4; df ¼ 25; p ¼ 0.176 t ¼ 1.4; df ¼ 24; p ¼ 0.189 t ¼ 1.0; df ¼ 25; p ¼ 0.347 c2 ¼ 0.1; df ¼ 1; p ¼ 0.745 t ¼ 0.6; df ¼ 25; p ¼ 0.571 t ¼ 0.8; df ¼ 25; p ¼ 0.447 t ¼ 1.9; df ¼ 25; p ¼ 0.069 t ¼ 0.5; df ¼ 25; p ¼ 0.597 t ¼ 0.1; df ¼ 25; p ¼ 0.991 t ¼ 0.1; df ¼ 25; p ¼ 0.955 t ¼ 0.7; df ¼ 25; p ¼ 0.487 t ¼ 1.3; df ¼ 25; p ¼ 0.210 t ¼ 2.6; df ¼ 24; p ¼ 0.016* t ¼ 0.7; df ¼ 25; p ¼ 0.524 c2 ¼ 0.1; df ¼ 1; p ¼ 0.863

*p-Values <0.05; with ¼ measurement with medication; without ¼ measurement without medication.

M. Schecklmann et al. / Journal of Psychiatric Research 45 (2011) 1463e1470

combined and five for the inattentive subtype of ADHD according to DSM-IV. In an exploratory approach we calculated group comparisons between the two subtype groups for the dependent variables (Sniffin’ Sticks and brain activation). We found no significant differences (t ¼ 1.1; df ¼ 25; p > 0.281) and abstained from further subtype analyses. All patients were on constant medication with MPH, 10 (of 27) patients presented with comorbid oppositional defiant disorder, one with elimination disorder, and one with specific phobia. In the control subjects neurological and psychiatric diagnoses were excluded by introductory interview. All participants were screened for psychiatric symptoms by parental ratings based on the “Child Behavior Checklist” (CBCL) (Achenbach and Rescorla, 2001) and an ADHD rating scale assessing the DSM-IV criteria (ADHS-DC) (Rösler et al., 2004). All children completed a questionnaire for depressive symptoms (“Depressionsinventar für Kinder und Jugendliche” (DIKJ) (Stiensmeier-Pelster et al., 2000), and impulsivity (“Inventar zur Erfassung von Impulsivität, Risikoverhalten und Empathie”; IVE)) (Eysenck et al., 1990; Stadler et al., 2004). Groups did not differ in age, handedness, and intelligence (Table 1). Intelligence was assessed in a clinical setting prior to study participation resulting in the use of different instruments (Grundintelligenztest (Weiss and Osterland, 1997; Weiss, 1998); Hamburg-Wechsler-Intelligenztest für Kinder III (Teves et al., 1999); Kaufman Assessment Battery for Children (Melchers and Preuss, 2001)). Both groups differed significantly in gender distribution, thus gender was introduced as covariate. Healthy controls were recruited via newspaper advertisement, sport clubs, flyers etc. Children with ADHD were rated higher on depressive (DIKJ), general problematic behavioural (CBCL), ADHD (ADHS-DC), and impulsivity (IVE) scales. 13 children with ADHD conducted the measurement first with ADHD medication and then without, 14 children vice versa. Those two ADHD groups based on the testing sequence did not differ significantly for all sample characteristics, for number of comorbidities, for overall intake time of medication, and intake time point of medication before the measurement under MPH (Table 1). Although they differed significantly for the washout period before the measurement without medication this did not seem to confound our results since both ADHD groups did not differ significantly in regard to olfactory function and fNIRS data (t < 1.2; df ¼ 25; p > 0.227). The minimum wash-out period was 14 half-lives of MPH. The study was approved by the Ethics Committee of the University of Wuerzburg. All participants and their parents gave written informed consent after comprehensive explanation of the procedures.

2.2. Measurement of olfactory function To obtain objective, reliable, and valid data for olfactory function we used the Sniffin’ Sticks (Burghart Instruments, Germany) measuring odour sensitivity, discrimination, and identification. The sticks look like felt-tip pens, contain a tampon and a liquid odorant dissolved in propylene glycol (4% dilution with a total volume of 4 ml), and were presented to the blindfolded participants 1 cm in front of the nostrils (compare Fig. 1). In the sensitivity test, a triplet of sticks was presented with one stick containing a defined concentration of 2-phenylethanol and two odourless samples. The subject had to decide which of three sticks smells “like a rose” (scent of 2-phenylethanol). By a staircase method the concentration of 2-phenylethanol is varied (16 different concentrations from 0.00012 to 4%), and the individual sensitivity threshold can be obtained by averaging the last four reversal points. In the discrimination test the subjects had to decide 16 times which stick out of three had a smell distinct from the other two. The identification test consisting of 16 choices requires the identification of the smelled

odour from a choice of (Wolfensberger et al., 2000).

1465

four

verbally

presented

odours

2.3. Measurement of brain activity FNIRS was shown to have high validity (Huppert et al., 2006) and reliability (Plichta et al., 2006, 2007; Schecklmann et al., 2008a), and is apt to measure motorically active children and adults (Ehlis et al., 2008; Schecklmann et al., 2008b; Schecklmann et al., 2010; Schecklmann et al., 2011). For the fNIRS measurement we used a continuous multi-channel wave system (ETG-4000 Optical Topography System; Hitachi Medical Co., Japan) working with two different wavelengths (695  20 nm and 830  20 nm) and a time resolution of 10Hz to measure relative changes of absorbed near-infrared light. These changes are transformed into concentration changes of O2Hb and HHb as indicators for brain activity by means of a modified Beer-Lambert law (Obrig and Villringer, 2003). The unit is mmol*mm, i.e. changes of chromophore concentration depend on the path length of the near-infrared light. We used two identical square probe sets (plastic panels) of optodes (light emitters and detectors) for each side of the head. One probe set consisted of eight light emitters and eight detectors with an inter-optode distance of 30 mm. A measuring point of activation (channel) was defined as the region between one emitter and one detector. Thus one probe set consisted of 24 channels and covered an area of 9*9 cm on the scalp. The panels were fastened to the head by elastic straps. The probe sets were placed on the head with regard to the relevant standard positions of the international 10e20 system for EEG electrode placement (Jasper, 1958; Okamoto et al., 2004). The exact placement of the probe sets and an approximation of the inferior frontal temporal brain areas consequently covered by the NIRS optodes are shown in Fig. 2. Odour stimulus for the measurement of olfactory function was a custom made Sniffin’ Stick containing the pure olfactory stimulant 2-phenylethanol at 16% concentration based on various pre-studies we had performed. Subjects were seated on a comfortable chair with earplugs, were blindfolded and instructed to relax, avoid to clench their teeth and to breathe uniformly. The stimulus was presented 15 times for 10 s in a distance of 1cm in front of the nostrils followed by a jittered interval of 30e40 s without any stimulation. The measurement session lasted about 12 min. Before statistical analysis of fNIRS data, the high frequency portion of the signal was removed by calculating a moving average with a time window of 5 s. Slow drifts in the measurement were excluded by the use of a linear fitting resulting from calculation of the mean of the 10 s right before the olfactory stimulation and the mean of the interval between the 10th and 20th second after the stimulation. A mean trajectory for each condition was calculated by averaging the 15 repetitions. As brain activation is considered as an increase in O2Hb during a task, the trajectory for active brain areas or channels should increase during task and decrease thereafter for O2Hb. In accordance to our recent publication in adults ADHD patients we again abstained from analysing HHB due to concentration changes that were not conform to the haemodynamic response (Schecklmann et al., 2011). This phenomenon has previously been observed and is probably related to an alteration in vasodilatation in the inferior frontal cortex (for an overview Ehlis et al., 2005). For further analysis we defined the area under the curve for the time interval 5 s before and 15 s after the task indicating brain activation (Fig. 1). The beginning and end points of this interval correspond to the cut face of the activation trajectory and the zero line; this is due to the slow drifts correction. We applied regions of interest (ROI) analyses since fNIRS provides highest reliability at a cluster level (Plichta et al., 2006, 2007; Schecklmann et al., 2008a). We defined two ROIs covering parts of the temporal

1466

M. Schecklmann et al. / Journal of Psychiatric Research 45 (2011) 1463e1470

Fig. 1. Time courses and areas under the curve for fNIRS signals. (A) Illustration of the fNIRS signals analysis by means of areas under the curve as indicators for brain activity. (B) Areas under the curve for the four regions of interest. (C) Time courses of regions of interest.

and the inferior frontal cortex (Fig. 2) and for each we averaged the areas under the curves. The choice of ROIs was based on our previous findings with the here applied pure olfactory stimulus 2phenylethanol activating those two regions (Schecklmann et al., 2011). Association of channels and brain areas were deducted from the work of Okamoto and colleagues (Okamoto et al., 2004) (http://brain.job.affrc.go.jp/wordpress/), which interrelates EEG positions and fNIRS probe sets. Basal brain activation is indicated by one-sided t-tests against zero for the ROIs and by according t-maps interpolated for all channels over the whole probe-set for each hemisphere and each group separately.

calculated between Sniffin’ Sticks subtests with significant group differences and brain activation, and between impulsivity and Sniffin’ Sticks subtests and brain activation. Significant correlations were visually inspected and corrected by exclusion of outliers. As we used an ROI approach minimizing the problem of multiple testing we abstained from Bonferroni correction. In addition, according to previous experience with olfactory fNIRS paradigms we expected only small effects. Thus, conservative correction would not be adequate. All analyses were performed with MatLab 6.5 (The MathWorks, Inc., USA) and SPSS (SPSS Inc., USA). 3. Results

2.4. Statistical analyses 3.1. Olfactory function For group comparisons between controls and patients with and without medication we used analyses of variance with gender as covariate (ANCOVAs). For the comparison of measurements with and without medication within the patient group we used twosided Student t-tests. Pearson correlation coefficients were

Between-group contrasts (Fig. 3) between controls and patients with medication and between controls and patients without medication showed no significant differences for olfactory sensitivity (without medication: F ¼ 0.9; df ¼ 1.46; p ¼ 0.345; with

M. Schecklmann et al. / Journal of Psychiatric Research 45 (2011) 1463e1470

1467

Fig. 3. Olfactory functions.

showed a high effect size (h2 ¼ 0.140). Olfactory discrimination did not differ for controls and patients with medication (F ¼ 2.2; df ¼ 1.46; p ¼ 0.145). 3.2. Brain activity (Figs. 1 and 2)

Fig. 2. fNIRS probe sets and fNIRS activation. (A) Arrangement of the fNIRS probe sets. Numbers indicate measurement channels. Channels in red and blue ink indicate the regions of interest temporal and inferior frontal cortex. Channels in black ink represent channels of no interest. Probe sets were geared to and measured cortical regions were concluded from particular electrode positions according to the international 10e20 system. (B) T-maps of brain activation as elicited by t-tests against zero (for interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).

medication: F ¼ 0.3; df ¼ 1.47; p ¼ 0.569) and identification (without medication: F ¼ 0.2; df ¼ 1.46; p ¼ 0.667; with medication: F ¼ 0.1; df ¼ 1.46; p ¼ 0.855). Within-subject comparisons in the group of patients revealed no significant differences for sensitivity (t ¼ 0.4; df ¼ 26; p ¼ 0.732) and identification (t ¼ 0.4; df ¼ 26; p ¼ 0.675) between measurements with and without medication. For olfactory discrimination, patients without medication had higher scores in contrast to controls (F ¼ 7.5; df ¼ 1.46; p ¼ 0.009) and in contrast to the measurement with medication with a statistical trend (t ¼ 1.9; df ¼ 26; p ¼ 0.068). The significant difference between patients without medication and controls

Controls showed positive activation in the four ROIs (left IFC: t ¼ 1.7; df ¼ 21; p ¼ 0.053; right IFC: t ¼ 2.1; df ¼ 21; p ¼ 0.022; left TC: t ¼ 0.9; df ¼ 21; p ¼ 0.178; right TC: t ¼ 1.6; df ¼ 21; p ¼ 0.067) during the presentation of 2-phenylethanol, i.e., oxygenated haemoglobin increased during olfactory stimulation and decreased thereafter. This activation was weak as indicated by one ROI with significant effects and by two ROIs with marginal significant effects. Patients showed no significant brain activations irrespective of medication status. Patients showed even decreases during the stimulation period with peaks after the olfactory stimulation. Except for the medicated condition small positive time courses were found for the right temporal cortex. Controls showed significantly higher activation in contrast to the patients without medication in all ROIs (left IFC: F ¼ 6.4; df ¼ 1,46; p ¼ 0.015; right IFC: F ¼ 7.7; df ¼ 1,46; p ¼ 0.008; left TC: F ¼ 7.8; df ¼ 1,46; p ¼ 0.007; right TC: F ¼ 5.2; df ¼ 1,46; p ¼ 0.028) and in contrast to the patients with medication in the left (F ¼ 6.6; df ¼ 1,46; p ¼ 0.014) and right IFC (F ¼ 3.6; df ¼ 1,46; p ¼ 0.064), but not in the left (F ¼ 2.2; df ¼ 1,46; p ¼ 0.141) and right TC (F ¼ 1.5; df ¼ 1,46; p ¼ 0.229). Patients with medication showed no differences in brain activation in contrast to the measurement without medication for the left IFC (t ¼ 0.6; df ¼ 26; p ¼ 0.573), for the right IFC (t ¼ 1.3; df ¼ 26; p ¼ 0.206), and for the right TC (t ¼ 1.3; df ¼ 26; p ¼ 0.215); left TC was significantly associated with lower negative oxygenation during medication than without medication (t ¼ 2.1; df ¼ 26; p ¼ 0.044). 3.3. Correlations Correlations between olfactory discrimination and oxygenation in the particular ROIs were not significant. We found no significant correlations between activity in left and right inferior frontal and temporal cortex with olfactory discrimination for controls and patients in both medication conditions. Only patients without medication showed significant correlations of left inferior frontal (r ¼ 0.404; p ¼ 0.037) and left temporal cortex activation (r ¼ 0.436; p ¼ 0.023) with olfactory discrimination, i.e., the higher the activation the lower the discrimination performance.

1468

M. Schecklmann et al. / Journal of Psychiatric Research 45 (2011) 1463e1470

4. Discussion We comprehensively investigated the effects of MPH treatment on olfactory function in 27 children with ADHD and 22 matched controls in regard to sensitivity, discrimination, and identification. In our previous investigation two independent patient groups of chronically medicated and medication-naïve ADHD patients were investigated in a between-group design revealing higher olfactory sensitivity in the untreated patient group. Here, we investigated MPH effects in patients with chronic MPH medication in a withingroup design. Half of the patients were assessed once during their regular prescribed intake of medication and again after cessation of treatment, while the other half was first assessed without, then after reinstatement of pharmacological treatment. In contrast to our previous finding, sensitivity did not differ significantly between patients without medication and controls and no medication effect on sensitivity was found (Romanos et al., 2008). However, we found significant differences for olfactory discrimination in the unmedicated condition between patients and controls while MPH treatment led to normalisation of discrimination. Both in our previous as well as in this study we determined improved olfaction in ADHD in the non-medicated condition and its normalisation by methylphenidate, yet in two distinct olfactory domains. Since in both cases we found strong effect sizes we consider our results to be valid. We assume that the methodological differences between both investigations may underlie the discrepant affection of olfactory domains. Our current finding suggests that cessation of stimulant medication exerts effects on olfactory function within several days leading to improved capability to discern distinct odours (discrimination), whereas our previous report captured chronic medication effects resulting in normalisation in olfactory sensitivity. Since both olfactory discrimination and sensitivity are considered as early functions of the olfactory bulb that is substantially modulated by dopaminergic neurotransmission (Halasz and Shepherd, 1983; Hsia et al., 1999; Cleland and Sethupathy, 2006), it is tempting to speculate that both increased sensitivity in medication-naïve patients and its normalisation with MPH treatment as well as increased discrimination induced by cessation of MPH treatment in patients with chronic medication may be related to modulation of dopaminergic neurotransmission. While acute MPH effects are generally attributed to blockade of the dopamine transporter that is highly expressed in the basal ganglia and to some extent as well in the olfactory bulb, the mechanisms of chronic MPH effects and their reversal are not very well understood on a molecular level (Thanos et al., 2008). We previously hypothesized that alterations in olfactory function in ADHD may be related to modulation in dopaminergic neurogenesis in the olfactory bulb (Romanos et al., 2008). Dopaminergic interneurons in the olfactory bulb are submitted to constant renewal, as stem cell in the subventricular zone migrate into the olfactory bulb within several weeks thus differentiating to inhibitory dopaminergic neurons (Whitman and Greer, 2009; Arenkiel, 2010). Some post-mortem studies found increased numbers of dopaminergic interneurons in the olfactory bulbs of patients with Parkinson’s disease. These findings along with animal models suggest that striatal dopaminergic cell loss may result in a compensatory increase of neurogenesis in the subventricular zone thus impairing olfactory function due to increased inhibition on olfactory information in the olfactory bulb (Huisman et al., 2004; Borta and Hoglinger, 2007; Berendse and Ponsen, 2009). One speculative explanation for improved olfaction in ADHD may be the hypothesis that alterations in striatal dopaminergic function in ADHD could lead to decreased neurogenesis thus resulting in decreased dopaminergic tone in the olfactory bulb. However, to confirm or refute this notion further studies are necessary. We

therefore conclude that modulation of the dopamine system by stimulant medication may on the one hand induce long-term effects on olfactory function (indicated by normalization of increased sensitivity by MPH) and their reversal may constitute in increased discrimination after cessation of MPH. Thus, the lack of improvement of olfactory sensitivity in this study may possibly be due to insufficient cessation time. Although both olfactory sensitivity as well as discrimination are considered to be mainly mediated by function of the olfactory bulb, the temporal and functional interplay between both remains elusive (Friedrich, 2006; Cave and Baker, 2009). Further studies are required for validation of this hypothesis and to further elucidate the temporal characteristics of olfactory modulation exerted by dopaminergic medication. Potential confounding may be due to sample characteristics. We here included five children with inattentive subtype in contrast to our previous study with combined type only; however, explorative analyses revealed no bias due to the inattentive subtype. Furthermore, in our previous study children in average were 2 years younger; thus our findings may possibly be indicative of developmental changes in the olfactory system during childhood. The hedonic value of odours has been shown to modulate brain activity in patients with Parkinson’s disease and should therefore be controlled for in future studies (Hummel et al., 2010). In line with our previous study in adults, controls displayed bilateral activation of inferior frontal cortex (IFC) and temporal cortex (TC) while activation in ADHD was overall diminished following cessation of MPH treatment (Schecklmann et al., 2011). While activation during MPH treatment was still reduced in IFC, brain activation during MPH intake to some extent normalized in TC, although activation did not reach the level of controls. Even if activity in frontal and temporal neocortex during passive smelling is a common finding (Fladby et al., 2004; Ishimaru et al., 2004a, 2004b; Royet and Plailly, 2004; Harada et al., 2006; Kobayashi et al., 2007; Lombion et al., 2008), the functional relevance of these areas in olfactory processing remains an open question. It is assumed that higher cognitive functions such as odour evaluation and semantic processes are mediated in these areas (Kobal and Kettenmann, 2000; Savic, 2002; Royet and Plailly, 2004). Several imaging studies showed IFC and TC activation during olfactory discrimination tasks (Savic et al., 2000; Kareken et al., 2003; Plailly et al., 2007). Here, negative correlations between olfactory discrimination and brain activity in left IFC and TC in patients after cessation of MPH support the notion that alterations in discrimination are in part mediated by temporal cortex function, while no correlation was present in those participants (controls and patients with MPH) that displayed normal discrimination and normal or normalized brain activity. Furthermore, the fact that lower temporal cortex brain activation was correlated with better discrimination further supports our data indicating that ADHD children after cessation of MPH display improved discrimination, while medication seems to normalize both olfactory function and temporal cortex activation. No significant correlations were found on the right hemisphere neither for controls nor for patients after cessation of MPH or during standard MPH treatment. Time courses in the patient group indicated not only decreases (i.e. a negative trajectory), but also a delayed peaking after the stimulation. Negative fMRI signals are considered to hyperpolarisation or inhibition as evoked in cortical tissue around activated areas (Harel et al., 2002; Devor et al., 2007). Fukuda and colleagues explored the fNIRS time courses during cognitive tasks and could present valid data that particular mental diseases are associated with particular trajectories (Suto et al., 2004). Schizophrenia seems to be associated with additional fNIRS signal peaks that are interpreted as inefficient cognitive recruitment. However, deactivations with delayed peaks in the patient group e as found in

M. Schecklmann et al. / Journal of Psychiatric Research 45 (2011) 1463e1470

our study e are still difficult to interpret and might constitute an expression of blood flow reallocation. We suggest conducting fMRI studies in the future to shed more light on this open question. The lack of frontal activation increase mediated by MPH may be surprising since the frontal cortex is subjected to substantial dopaminergic modulation (Seamans and Yang, 2004). Furthermore, frontal cortex dysfunction has been repeatedly discussed as the neural substrate of core deficits in ADHD aetiopathology (Schecklmann et al., 2010) and various neuropsychological studies found normalizing effects through stimulant medication on deficient executive function related to prefrontal cortex functioning (Seifert et al., 2003; Rubia et al., 2009). However, several structural and functional findings highlight the role of temporal cortex in ADHD (Kaya et al., 2002; Kim et al., 2002; Lorberboym et al., 2004; Akay et al., 2006; Schneider et al., 2006). For example, Akay and colleagues found an improvement in temporal hypoperfusion after two months of MPH treatment. Although some authors explicitly suggest broadening the focus of ADHD research beyond the frontostriatal areas to the more neglected temporal cortex, only few imaging studies in ADHD investigated the lateral temporal cortex during cognitive tasks (Rubia et al., 2007; Kobel et al., 2009). We previously reported in an fNIRS study altered inferior frontal and temporal activity during verbal fluency tasks in adult ADHD (Schecklmann et al., 2008b). This is in line with findings in fMRI studies implicating the lateral temporal cortex with working memory and selective attention (Banich et al., 2001; Collette et al., 2001). Imaging studies during perception of odours indicate that apart from its relevance for odour discrimination the temporal cortex plays an important role in odour memory (Kobal and Kettenmann, 2000; Savic et al., 2000). In conclusion, we found effects on olfactory function both at a behavioural (olfactory discrimination) as well as a functional level (temporal brain activity) after cessation of chronic MPH treatment in children with ADHD. In light of the present and former findings (Romanos et al., 2008; Schecklmann et al., 2011) we conclude that ADHD is accompanied by alterations in olfactory function on a behavioural as well as a central functional level. We furthermore conclude that intake of MPH exerts normalizing effects on both levels, although our findings suggest differential effects by chronic treatment vs. rather immediate cessation effects that are presumably related to modulation of the dopaminergic system. Olfactory function may be a promising candidate as biomarker of altered dopaminergic function in ADHD and may be a useful tool to monitor treatment effects. Conflict of interest All the authors declare that they have no conflicts of interest. Contributors The authors Schecklmann and Romanos designed the study, wrote the protocol, managed the literature researches, and wrote the first draft of the manuscript. The author Schecklmann undertook the analyses. The authors Schecklmann, Romanos, Schaldecker, Aucktor, Brast, and Kirchgäßner recruited and measured patients and were involved in analyses. All the authors contributed to and have approved the final manuscript. Role of funding source The study was supported by the Deutsche Forschungsgemeinschaft, KFO 125 without a further role in study design, collection, analysis and interpretation of data, in the writing of the report and in the decision to submit the paper for publication.

1469

Acknowledgements The authors would like to thank Hitachi Medical Corporation for the ETG-4000 equipment and the skilled technical and methodical support. References Achenbach TM, Rescorla LA. Manual for the ASEBA School-Age Forms & Profiles. Burlington: University of Vermont, Research Center for Children, Youth, Families; 2001. Akay AP, Kaya GC, Emiroglu NI, Aydin A, Monkul ES, Tasci C, et al. Effects of longterm methylphenidate treatment: a pilot follow-up clinical and SPECT study. Progress in Neuro-Psychopharmacology and Biological Psychiatry 2006;30: 1219e24. Albrecht J, Wiesmann M. The human olfactory system. Anatomy and physiology. Nervenarzt 2006;77:931e9. Arenkiel BR. Adult neurogenesis supports short-term olfactory memory. Journal of Neurophysiology 2010;103:2935e7. Banich MT, Milham MP, Jacobson BL, Webb A, Wszalek T, Cohen NJ, et al. Attentional selection and the processing of task-irrelevant information: insights from fMRI examinations of the Stroop task. Progress in Brain Research 2001;134:459e70. Berendse HW, Ponsen MM. Diagnosing premotor Parkinson’s disease using a twostep approach combining olfactory testing and DAT SPECT imaging. Parkinsonism Related Disorders 2009;15(Suppl. 3):S26e30. Borta A, Hoglinger GU. Dopamine and adult neurogenesis. Journal of Neurochemistry 2007;100:587e95. Cave JW, Baker H. Dopamine systems in the forebrain. Advances in Experimental Medicine and Biology 2009;651:15e35. Cleland TA, Sethupathy P. Non-topographical contrast enhancement in the olfactory bulb. BMC Neuroscience 2006;7:7. Collette F, Van der Linden M, Dabe P, Degueldre C, Delfiore G, Luxen A, et al. Contribution of lexico-semantic processes to verbal short-term memory tasks: a PET activation study. Memory 2001;9:249e59. Devor A, Tian P, Nishimura N, Teng IC, Hillman EM, Narayanan SN, et al. Suppressed neuronal activity and concurrent arteriolar vasoconstriction may explain negative blood oxygenation level-dependent signal. Journal of Neuroscience 2007;27:4452e9. Ehlis AC, Bahne CG, Jacob CP, Herrmann MJ, Fallgatter AJ. Reduced lateral prefrontal activation in adult patients with attention-deficit/hyperactivity disorder (ADHD) during a working memory task: a functional near-infrared spectroscopy (fNIRS) study. Journal of Psychiatric Research 2008;42:1060e7. Ehlis AC, Herrmann MJ, Wagener A, Fallgatter AJ. Multi-channel near-infrared spectroscopy detects specific inferior-frontal activation during incongruent Stroop trials. Biological Psychology 2005;69:315e31. Eysenck SBG, Daum I, Schugens MM, Diehl JM. I7 IMPULSIVITAETSFRAGEBOGEN NACH EYSENCK impulsiveness, venturesomeness, and empathy in adults (IVE; Eysenck, Pearson, Easting, Allsopp, 1985) e German version/author Synonym(e): Eysenck Impulsiveness Questionnaire; 1990. Fladby T, Bryhn G, Halvorsen O, Rose I, Wahlund M, Wiig P, et al. Olfactory response in the temporal cortex of the elderly measured with near-infrared spectroscopy: a preliminary feasibility study. Journal of Cerebral Blood Flow and Metabolism 2004;24:677e80. Friedrich RW. Mechanisms of odor discrimination: neurophysiological and behavioral approaches. Trends in Neurosciences 2006;29:40e7. Gansler DA, Fucetola R, Krengel M, Stetson S, Zimering R, Makary C. Are there cognitive subtypes in adult attention deficit/hyperactivity disorder? The Journal of Nervous and Mental Disease 1998;186:776e81. Genro JP, Kieling C, Rohde LA, Hutz MH. Attention-deficit/hyperactivity disorder and the dopaminergic hypotheses. Expert Review of Neurotherapeutics 2010; 10:587e601. Halasz N, Shepherd GM. Neurochemistry of the vertebrate olfactory bulb. Neuroscience 1983;10:579e619. Harada H, Tanaka M, Kato T. Brain olfactory activation measured by near-infrared spectroscopy in humans. Journal of Laryngology & Otology 2006;120:638e43. Harel N, Lee SP, Nagaoka T, Kim DS, Kim SG. Origin of negative blood oxygenation level-dependent fMRI signals. Journal of Cerebral Blood Flow and Metabolism 2002;22:908e17. Hsia AY, Vincent JD, Lledo PM. Dopamine depresses synaptic inputs into the olfactory bulb. Journal of Neurophysiology 1999;82:1082e5. Huisman E, Uylings HB, Hoogland PV. A 100% increase of dopaminergic cells in the olfactory bulb may explain hyposmia in Parkinson’s disease. Movement Disorders 2004;19:687e92. Hummel T, Witt M, Reichmann H, Welge-Luessen A, Haehner A. Immunohistochemical, volumetric, and functional neuroimaging studies in patients with idiopathic Parkinson’s disease. Journal of Neurological Sciences 2010;289:119e22. Huppert TJ, Hoge RD, Diamond SG, Franceschini MA, Boas DA. A temporal comparison of BOLD, ASL, and NIRS hemodynamic responses to motor stimuli in adult humans. Neuroimage 2006;29:368e82. Ishimaru T, Yata T, Hatanaka-Ikeno S. Hemodynamic response of the frontal cortex elicited by intravenous thiamine propyldisulphide administration. Chemical Senses 2004a;29:247e51.

1470

M. Schecklmann et al. / Journal of Psychiatric Research 45 (2011) 1463e1470

Ishimaru T, Yata T, Horikawa K, Hatanaka S. Near-infrared spectroscopy of the adult human olfactory cortex. Acta Otolaryngol Supplement; 2004b:95e8. Jasper HH. The ten-twenty electrode system of the International Federation. Electroencephalography and Clinical Neurophysiology 1958;10:371e5. Kareken DA, Mosnik DM, Doty RL, Dzemidzic M, Hutchins GD. Functional anatomy of human odor sensation, discrimination, and identification in health and aging. Neuropsychology 2003;17:482e95. Karsz FR, Vance A, Anderson VA, Brann PG, Wood SJ, Pantelis C, et al. Olfactory impairments in child attention-deficit/hyperactivity disorder. Journal of Clinical Psychiatry 2008;69:1462e8. Kaufman J, Birmaher B, Brent D, Rao U, Flynn C, Moreci P, et al. Schedule for affective disorders and schizophrenia for school-age children-present and lifetime version (K-SADS-PL): initial reliability and validity data. Journal of American Academy of Child and Adolescent Psychiatry 1997;36:980e8. Kaya GC, Pekcanlar A, Bekis R, Ada E, Miral S, Emiroglu N, et al. Technetium-99m HMPAO brain SPECT in children with attention deficit hyperactivity disorder. Annals of Nuclear Medicine 2002;16:527e31. Kim BN, Lee JS, Shin MS, Cho SC, Lee DS. Regional cerebral perfusion abnormalities in attention deficit/hyperactivity disorder. Statistical parametric mapping analysis. European Archives of Psychiatry and Clinical Neuroscience 2002;252: 219e25. Kobal G, Kettenmann B. Olfactory functional imaging and physiology. International Journal of Psychophysiology 2000;36:157e63. Kobayashi E, Kusaka T, Karaki M, Kobayashi R, Itoh S, Mori N. Functional optical hemodynamic imaging of the olfactory cortex. Laryngoscope 2007;117: 541e6. Kobel M, Bechtel N, Weber P, Specht K, Klarhofer M, Scheffler K, et al. Effects of methylphenidate on working memory functioning in children with attention deficit/hyperactivity disorder. European Journal of Paediatric Neurology 2009; 13:516e23. Levy F, Swanson JM. Timing, space and ADHD: the dopamine theory revisited. Australian and New Zealand Journal of Psychiatry 2001;35:504e11. Lombion S, Comte A, Tatu L, Brand G, Moulin T, Millot JL. Patterns of cerebral activation during olfactory and trigeminal stimulations. Human Brain Mapping; 2008. Lorberboym M, Watemberg N, Nissenkorn A, Nir B, Lerman-Sagie T. Technetium 99m ethylcysteinate dimer single-photon emission computed tomography (SPECT) during intellectual stress test in children and adolescents with pure versus comorbid attention-deficit hyperactivity disorder (ADHD). Journal of Child Neurology 2004;19:91e6. Melchers P, Preuss U. K-ABC Kaufman Assessment Battery for Children. Deutsche Version. Goettingen: Hogrefe Verlag; 2001. Murphy KR, Barkley RA, Bush T. Executive functioning and olfactory identification in young adults with attention deficit-hyperactivity disorder. Neuropsychology 2001;15:211e20. Obrig H, Villringer A. Beyond the visibleeimaging the human brain with light. Journal of Cerebral Blood Flow and Metabolism 2003;23:1e18. Okamoto M, Dan H, Sakamoto K, Takeo K, Shimizu K, Kohno S, et al. Threedimensional probabilistic anatomical cranio-cerebral correlation via the international 10e20 system oriented for transcranial functional brain mapping. Neuroimage 2004;21:99e111. Plailly J, Radnovich AJ, Sabri M, Royet JP, Kareken DA. Involvement of the left anterior insula and frontopolar gyrus in odor discrimination. Human Brain Mapping 2007;28:363e72. Plichta MM, Herrmann MJ, Baehne CG, Ehlis AC, Richter MM, Pauli P, et al. Eventrelated functional near-infrared spectroscopy (fNIRS): are the measurements reliable? Neuroimage 2006;31:116e24. Plichta MM, Herrmann MJ, Baehne CG, Ehlis AC, Richter MM, Pauli P, et al. Eventrelated functional near-infrared spectroscopy (fNIRS) based on craniocerebral correlations: Reproducibility of activation? Human Brain Mapping 2007;28: 733e41. Polanczyk G, Rohde LA. Epidemiology of attention-deficit/hyperactivity disorder across the lifespan. Current Opinions in Psychiatry 2007;20:386e92. Romanos M, Renner TJ, Schecklmann M, Hummel B, Roos M, von Mering C, et al. Improved odor sensitivity in attention-deficit/hyperactivity disorder. Biological Psychiatry 2008;64:938e40.

Romanos M, Weise D, Schliesser M, Schecklmann M, Loffler J, Warnke A, et al. Structural abnormality of the substantia nigra in children with attentiondeficit hyperactivity disorder. Journal of Psychiatry and Neuroscience 2010; 35:55e8. Rösler M, Retz W, Retz-Junginger P, Thome J, Supprian T, Nissen T, et al. Tools for the diagnosis of attention-deficit/hyperactivity disorder in adults. Self-rating behaviour questionnaire and diagnostic checklist. Nervenarzt 2004;75:888e95. Royet JP, Plailly J. Lateralization of olfactory processes. Chemical Senses 2004;29: 731e45. Rubia K, Halari R, Cubillo A, Mohammad AM, Brammer M, Taylor E. Methylphenidate normalises activation and functional connectivity deficits in attention and motivation networks in medication-naive children with ADHD during a rewarded continuous performance task. Neuropharmacology 2009;57:640e52. Rubia K, Smith AB, Brammer MJ, Taylor E. Temporal lobe dysfunction in medicationnaive boys with attention-deficit/hyperactivity disorder during attention allocation and its relation to response variability. Biological Psychiatry 2007;62: 999e1006. Savic I. Imaging of brain activation by odorants in humans. Current Opinion in Neurobiology 2002;12:455e61. Savic I, Gulyas B, Larsson M, Roland P. Olfactory functions are mediated by parallel and hierarchical processing. Neuron 2000;26:735e45. Schecklmann M, Ehlis AC, Plichta MM, Fallgatter AJ. Functional near-infrared spectroscopy: a long-term reliable tool for measuring brain activity during verbal fluency. Neuroimage 2008a;43:147e55. Schecklmann M, Ehlis AC, Plichta MM, Romanos J, Heine M, Boreatti-Hummer A, et al. Diminished prefrontal oxygenation with normal and above-average verbal fluency performance in adult ADHD. Journal of Psychiatric Research 2008b;43: 98e106. Schecklmann M, Romanos M, Bretscher F, Plichta MM, Warnke A, Fallgatter AJ. Prefrontal oxygenation during working memory in ADHD. Journal of Psychiatric Research 2010;44:621e8. Schecklmann M, Schenk E, Maisch A, Kreiker S, Jacob C, Warnke A, et al. Altered frontal and temporal brain function during olfactory stimulation in adult attention-deficit/hyperactivity disorder. Neuropsychobiology 2011;63:66e76. Schneider M, Retz W, Coogan A, Thome J, Rosler M. Anatomical and functional brain imaging in adult attention-deficit/hyperactivity disorder (ADHD) e a neurological view. European Archives of Psychiatry and Clinical Neuroscience 2006; 256(Suppl. 1):i32e41. Seamans JK, Yang CR. The principal features and mechanisms of dopamine modulation in the prefrontal cortex. Progress in Neurobiology 2004;74:1e58. Seifert J, Scheuerpflug P, Zillessen KE, Fallgatter A, Warnke A. Electrophysiological investigation of the effectiveness of methylphenidate in children with and without ADHD. Journal of Neural Transmission 2003;110:821e9. Sontag TA, Hauser J, Kaunzinger I, Gerlach M, Tucha O, Lange KW. Effects of the noradrenergic neurotoxin DSP4 on spatial memory in the rat. Journal of Neural Transmission 2008;115:299e303. Stadler C, Janke W, Schmeck K. Inventar zur Erfassung von Impulsivität, Risikoverhalten und Empathie bei 9- bis 14-jährigen Kindern (IVE). Göttingen, Germany: Hogrefe; 2004. Stiensmeier-Pelster J, Schürmann M, Duda K. Depressionsinventar für Kinder und Jugendliche. Deutsche Version des Children’s Depression Inventory; 2000. Suto T, Fukuda M, Ito M, Uehara T, Mikuni M. Multichannel near-infrared spectroscopy in depression and schizophrenia: cognitive brain activation study. Biological Psychiatry 2004;55:501e11. Teves U, Schallberger P, Rossmann U. Hamburg-Wechsler-Intelligenztest für Kinder III (HAWIK-III). Bern: Huber; 1999. Thanos PK, Michaelides M, Benveniste H, Wang GJ, Volkow ND. The effects of cocaine on regional brain glucose metabolism is attenuated in dopamine transporter knockout mice. Synapse 2008;62:319e24. Weiss RH. Grundintelligenztest Skala 2 CFT 20. Goettingen: Hogrefe Verlag; 1998. Weiss RH, Osterland J. Grundintelligenztest Skala 1 CFT 1. Goettingen: Hogrefe Verlag; 1997. Whitman MC, Greer CA. Adult neurogenesis and the olfactory system. Progress in Neurobiology 2009;89:162e75. Wolfensberger M, Schnieper I, Welge-Lussen A. Sniffin’Sticks: a new olfactory test battery. Acta Otolaryngology 2000;120:303e6.