Middle latency components of evoked potential responses in schizophrenics

Brief Reports

BIOL PSYCHIATRY 1986;21:1097-1100

Middle Latency Components Responses in Schizophrenics

1097

of Evoked Potential

C. R. Mukundan

Introduction Middle latency components (PlOO-PI, Nl40-N 1, and P200-P2) of evoked potentials in schizophrenia are generally reported to show attenuation compared with those of normal controls (Buchsbaum 1977). These components have been considered to be related to selective attention and its maintenance (Schwent et al. 1976). Pfefferbaum et al. ( 1980), on the other hand, reported that schizophrenics had larger auditory components co~esponding to PI and P2 (only P2 was statistically significant; Pl showed a trend in a small sample), whereas corresponding Nl was significantly reduced in amplitude compared with that of the controls. The aims of the present study were to elicit further evidence with respect to the latency and amplitude measures of middle components and the pattern of habituation over repeated presentation of flashes and tones in schizophrenics.

Methods The schizophrenic group consisted of 29 patients who were selected on the basis of Research Diagnostic Criteria (Spitzer et al. 1978)

Fromthe Clinical

Neuropsychoiogy Laboratory. Department ofClinical Psychology, National Institute of Mental Health and NeuroSc~ences. Bangalore, India. Supported in part by Grant 514.8/8 I -NCD- 1 from the Indian Council of Medical Research. Address reprint requests to Dr. C.R. chology Laboratory, institute of Mental

Department

Mukundan. of Clinical

Health and NeumSciences.

Clinical

Bangalore

India. Received October

0

1986 Society

2. 1985: revised November

of Biological

Psychiatry

Neuropsy-

Psychology,

26.

19X5.

National 560029.

and who were unmedicated at the time of the experiment. Their mean age was 27.5 years (SD 7.5). The control group consisted of 29 normal subjects with a mean age of 26.4 years (SD 6.9). There were 15 men and 14 women in each group. These subjects did not have any previous history of neurological or psychiatric disorder for which they were under treatment. The subject was comfortably seated in a dimly lighted (4 lux) soundproof room, and Nihon Kohden SLS4100 photic and SSS 1101 sonic stimulators were used to present stimuli through a microprocessorcontrolled stimulus programmer system. The intensity of the flash was 2 J, and a 60-dB tone of lOOO-Hz frequency and lOO-msec duration was the auditory stimulus. Both stimuli were presented at a constant interval of 3 sec. The electrode positions used were P4-Cz-P3 and T4Cz-T3, as defined by the lo-20 international system, for the visual and auditory paradigms respectively. AB620G bioamplifiers (Nihon Kohden) were used for signal conditioning, with a time constant of 2 set and high-frequency cutoff of 100 Hz. Averaging was done on an Iwatsu SM2lOOB Signal Analyser. Analysis duration was 250 msec, and the two channels were calibrated using the input:output ratio of the bioampli~ers for a 50-pV calibrating signal; 64 artifact-free sweeps were captured on a floppy diskette for later averaging. During the analysis, the averaging was halted at the 9th averaging, and the latencies and amplitudes of PIOO, N140, and P200 components were measured; the same were measured again after the 64th averaging. All experiments were done with eyes open.

0006-3223/86/$03.50

1098

Brief Report3

BIOL PSYCHIATRY 1986;21:1097-1100

An artifact rejection facility using the usual A/D convertor overflow rejection method was available in the computer system used. The recordings were taken with the A/D convertor charged to three-fourths. In this study, it was also possible to reject a file with artifacts, especially low-amplitude myogenic artifacts. as the analysis was done off line. In that event. the data in the rejected tile were replaced by data from the preceding tile. However, this was very infrequently done. An on-line editing facility was also employed, which disabled the stimulator so that the trigger pulse did not reach the averager. Electroencephalogram (EEG) was separately monitored on a C scope.

PlOO

L

Results The mean latencies and standard deviations in visual and auditory modalities for the two groups after the 64th averaging are given in Table I.

Amplitudes

and Habituation

RP70

c

Pattern

Amplitude was measured as peak-to-peak potential difference. In the visual paradigm (Figure I). the PI component in the patient group showed signifcant amplitude attenuation in the recordings made on the right (t = 2.40. p < 0.05) and the left (I = 2.98. p < 0.01) sides. The NI amplitude was markedly less. though the

Table I, Mean Latcncies and Standard Deviations of Visual and Auditory Evoked Potentials in Schizophrenic and Control Groups Control

Schizophrenic MeXI (msec 1

Mean SI)

(IlNXI

SD

ViWd

PI00 Nl40 P200

Y4.6 124.8 176.9

13.7 14.6 16.5

9X.4 124.5 177.3

Il.6 14.2 14.x

62.5 9x.4 161.4

10.5

63.7 I(M).4 163 3

IO.8 13.4 17.6

Audiro,l

P70 NIOO PI60

II.8 16.X

Figure I. The means and standard deviations of PI of visual evoked potential (a) and PI (b) and Nl ic) of auditory evoked potential in the schizophrenic and control groups. (a) Right. P4-CZ: left. P3-CZ. th and c) Right. T4-CZ: left. TS-CZ.

difference was statistically not significant. In the auditory paradigm, the PI showed significant attenuation in the right (t = 2.76. p < 0.01) and left (t = 2.46, p < 0.02) centrotemporal leads in the patients. With respect to the Nl amplitude, a lateralization effect seemed to appear as the amplitude in the patient group showed a significant (f = 2.59. 17 < 0.02) attenuation

BIOL PSYCHIATRY 1986;21:1097-1100

Brief Reports

on the left side. Hence, a median test was carried out on the difference scores of right minus left divided by the mean of right and left. However, the difference did not emerge as significant. There was no evidence of a significant difference in the mean amplitudes of P2 between the two groups in either paradigm. Comparison of the difference of amplitudes of the three components after the 9th and the 64th averagings showed that amplitude decrement of NlOO was significantly less in the patient group (Figure 2). The mean decrements of amplitudes of this potential in the patient group were 2.20 (SD 2.19) and 2.10 (SD 3.28) PV for the right and left leads, respectively, whereas the normal group showed mean decrements of 6.49 (SD 5.14) and 4.90 (SD 3.28) kV, respectively. Between-group comparisons of the amplitude decrements showed that the mean differences were significant (x2 = 7.25,~ < 0.01 for right and xz = 7.46, p < 0.01 for left). Analysis of difference scores of the NlOO amplitudes after the 9th averaging did not show a lateralization effect between the two groups, though within the control group, the left mean amplitude was significantly greater (t = 2.68, p < 0.02) than the right mean amplitude. However, this difference was not significant after the 64th averaging. The Pl, N140, and P2 components in both paradigms did show a trend of amplitude decrement, though it was not statis-

tically significant. It should be added that throughout the study, no sex differences were found.

Discussion Latency data are in agreement with the findings so far known, which indicate that a structural damage of the brain system involved in the electrogenesis of these potentials is not implied in schizophrenia. With respect to amplitude, though all three components in patients have shown attenuation, only PI amplitudes are significantly reduced in both paradigms. This could imply a dysfunction of the parietal area, which is considered to be a nonspecific source for the electrogenesis of these potentials other than the specific cortical sensory projection areas. Considering that N 100 has also shown a marked attenuation, postulation of a temporoparietal dysfunction in schizophrenia is generally supported, though a limbic influence on these deficits cannot be ruled out from these findings. There was no evidence for a lateralized dysfunction in schizophrenia. With respect to habituation of the NlOO component, the control group showed an average 46.4% decrement, whereas it was only 30.5% in the patients. A similar habituation effect with repeated auditory stimulation in cats was reported earlier by Calford (1983). This finding suggests that the range of responsiveness of the

Figure 2. The AEP after the 9th (top) and the 64th (bottom) averaging schizophrenic

250ms

in a normal subject

patient (b).

*

a

1099

b

(a) and a

I loo

UlOL PSYCHIATRY lY86;?1:1097- 1100

brain to external stimulation of certain intensity is reduced in patients in the clinical condition under investigation. Failure to observe similar effect with the photic stimuli may hc due to the greater intensity effect of the flashes. The differential effect on only one component can be understood only when the electrogenesis of these potentials is well established. Illustrative

averaging

on amplitude

digms are available

I wish

of AEP,

decrements

EPs of all subjects and data

for all components

in both para-

from the author by special request.

to thank Ms. Hema Nalini

for their help with these experiments.

and Mr. Rajan Mathai

References Buchsbaum MS ( 19771. The middle evohed response cots poncnts and \chwophrenw .S&i~~?hr R~rll 3:93- IOJ. C’,dford MB (1983): ‘The parcellatwn ot the medial penl~ ulate body of the cat defined by the auditory reaponw propcrtic\ of sqlc units. .I N~~N~o.\cI 3:2350 -2364 Ptrifcrbaum A. Horvath TB. Roth WT. Tlnklenberg JR. Kopell BS ( 1980): Au&tory bram stem and cortical evoked potential in \chiTophrenia. f?iol P.\\c,hi~rr\, IS:209 221 Schwcnt VI,. Snyder E, Hillyard SA (1970): i\uditor?; cwked potentials during multichannel wlectl\c listening cut\ I F.v/, P.\whoi 2:317~ 125