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impended adaptation to new conditions, in cases when a whole series of new connections has to be created, the formation of one or several of them blocks the further associative activity-the result is a generalization of partial, “accidental” connection.

442 SCHIZOPHRENIA AND LEFT FRONTO-TEMPORAL EEG ABNORMALITIES IN THE AFTERMATH OF THE CHERNOBYL DISASTER K.N. Loganovsky*, T.K., Loganovskaja Neurology Department, Institute for Clinical Radiology, Scientific Centre for Radiation Medicine, Academy of Medical Sciences of Ukraine, 53 Melnikov Street, Kiev, 254050 Ukraine Nakane and Ohta (1986) revealed very high (6%) prevalence rate of schizophrenia in A-bomb survivors. It has been carried out the epidemiological study of schizophrenia in the Chernobyl exclusion zone on the base of the Chernobyl psych@@ archives (1986-1997) analysis and registration of computerized 19-channel EEG, visual checkerboard (VEP) and somato-sensory evoked potentials (SSEP) in 100 patients who had a verified acute radiation sickness (ARS) and randomly selected 100 chronically irradiated Chernobyl disaster survivors, who have been working in the Chernobyl exclusion zone since 1986-87 during 5 and morf years. Since 1990 a significant increase (more than 4 times: 5.4 per 10,000 in the zone and 1.1 per 10,000 in Ukraine) in schizophrenia incidence has been taking place among the exclusion zone workers in comparison with the general population. The relative risks are 2.4 for 1986-1996 and 3.4 for 1990-1996 indicate that working and living in the exclusion>one is associated with more than twofold and even triple increase in the risk of schizophrenia onset. It has also been revealed that a statistically significant increase of the schizophrenia percentage amongst all psychoses in the exclusion zone personnel in comparison with the general Ukrainian population (73% vs 43% correspondingly). The relative risk is 1.7 and indicate that working and living in the exclusion zone is associated with practically a twofold (85%) increase in the risk of schizophrenia in the structure of psychoses. Schizophrenia takes a first place in the structure of the severe mental disorders of the exclusion zone personnel. The percentage of the schizophrenic psychoses to another psychoses in the exclusion zone personnel is very high: 79%. The schizophrenic psychoses related to the affective ones like 16:l. At the sametime a majority of the Chernobyl survivors irradiated by doses more than 0.30 Sv (including ARS-patients) had left front-temporal EEGabnormalities- on the background polymorphous “flat” (lowvoltage) EEG the paroxysmal activity (spikes, polyspikes, acute and &waves, sometimes-spike-wave) was shifted to the left fronto-temporal region. There was a s@ificant predominance of 6 and /?-(dominant frequency-20 Hz)-powers of EEG, particularly, in the frontal lobe also shifted to the left frontotemporal or parieto-temporal regions, that correlated with

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severity degree of ARS and, consequently, with absorbed doses of ionizing radiation. There was a depression 6 and a-range (especially in the left occipito-parietal region). Decreased VEP latency and increased amplitude for P,oO (p < 0.01) or a total deformation of main VEP components (P,,“, N~45 and Pzoo) associated with increased SSEP latencies and a decreased amplitude of late (PjoO and NdO,,) components together with an increased contralateral latency of N,, for right medianus nerve simulation. The cerebral hypothesis (structural and functional abnormalities of limbic system and the left hemisphere) for an explanation of an increase of the risk of schizophrenia and schizotypical disorders after exposure to ionizing radiation was proposed.

443 TRANSIENT SCHIZOPHRENIA

VISUAL

CHANNEL

FUNCTIONS

IN

S. K&i”‘*, A. Antal*, G. Szekeres’, G. Benedek2, Z. Janka’ Albert Szent-Gy@yi, Medical University, Departments of Psychiatry’ and *Physiology, Szeged, POB 1192, H-6701, HunWY The information-processing theories of schizophrenia hypothesize the overactivity of low spatial frequency-sensitive transient visual channels. The present study investigates this hypothesis, using visual contrast sensitivity (CS) measuremerits.-1.0never medicated, first-episode schizophrenic patients (7 male and 3 female, mean age: 21.5 f 7.4 years, mean duration of education: 11.5 f 3.4 years, mean BPRS score: 31.2 + 9.7) and 10 gender, age, and education matched healthy control subjects participated in the study. The CS was measured with a standard computerized test (Venus, NeuroScientific Corporation, USA). In this procedure the minimal luminance-contrast of grating stimuli, which is indispensable for the detection, is evaluated. This is the contrast threshold, and its inverse is the CS. In the static CS condition (SCS), 9 spatial frequencies (SFs) were tested (0.48, 1.19, 1.91, 2.87, 3.58, 4.78, 5.73,7.17, and 14.38 cpd). In the dynamic CS condition (DCS), a 4 Hz temporal modulation was used at the same SFs. In the SCS test, schizophrenics showed abnormally elevated CSs at the two lowest SFs (0.48 cpd (p < 0.001) and 1.19 cpd (p < 0.02)). In the DCS condition, CS was significantly higher in the schizophrenia group at the 3 lowest SFs (0.48 cpd (p < O.OOOl), 1.19 (p < 0.001) cpd, 1.91 cpd (p < 0.005)). In summary, there were selectively elevated CS values at the low SFs, which was more pronounced when a temporal modulation was used. These data suggest the overactivity of transient visual channels in schizophrenic patients.

444 EXECUTIVE CONTROL IS DISTURBED IN SCHIZOPHRENIA: EVIDENCE FROM EVENT-RELATED POTENTIALS IN A GO/NO GO TASK

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M. Weisbrod *l , M . Kiefer’, F. Marzinzik’, M. Scherg’, M. Spitzer 2 ‘University of Heidelberg, Department of Psychiatry, VossStrasse 4, Heidelberg, D-69115, Germany %niversity of Ulm The control of action and thought plays an important role in the organization of human behavior. Theories of attention have postulated an “executive control system” engaged in situations requiring decision making, conflict resolution, error correction, and response inhibition. Some schizophrenic symptoms can be conceptualized as failure of the “executive control system”. This system can be examined using go/no go tasks which require inhibition of a prepared response. In our study event related potentials (ERPs) were recorded while 16 healthy controls and 16 schizophrenic patients performed two different auditory go/no go tasks. In healthy controls two ERP effects were shown to be specifically associated with response inhibition: 1) A bilateral inferior frontal effect in the time window of the N2 ERP component. 2) An augmented fronto-central positivity in the time window of the P3 which was most prominent over left fronto-central electrode sites irrespective of the side of motor response. Source analyses suggested generators in the inferior prefrontal cortices to underly the effect in the N2 window, and sources near the frontal midline (approximately anterior cingulate cortex) and in the left premotor or motor cortex to underly the effect in the P3 window. In respect to the effect in the N2 window schizophrenic patients were not different from healthy controls. In contrast, the effect in the P3 window was significantly different between schizophrenic patients and controls. This finding points to dysfunctions in the anterior cingulate as the neuronal substrat of disturbed executive functions in schizophrenia.

445 ELECTROPHYSIOLOGICAL CORRELATES IMPAIRED A’ITENTION IN SCHIZOPHRENIA A. Basidska* Department of Psychiatry, Medical University Nowowiejska 27, Warsaw, 00-665, Poland

OF

of Warsaw,

50 male schizophrenic patients and 50 male age-matched volunteers performed the Continuous Attention Task (CAT). Target was defined as direct repetition of the same geometrical pattern. Visual potentials (VEP) evoked by CAT items were compared between the two groups and the differences were compared with CAT results. CAT revealed in patients signticantly higher index of errors (contributed by numerous omissions, while commission indices in both groups were comparable); lower detection index and longer reaction time, as compared to the control subjects. VEP examination re-

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vealed in patients 1) lower non-target amplitudes of components Pl, Nl and P3a; 2) change during detection of target, i.e. an increase of amplitudes of occipital and posterotemporal Nl as well as of frontal P3a, while in the control group no significant changes of amplitude of that components occurred 3) delayed target P2, N2 and P3a latencies 4) lower amplitude of target P3b. Atypical increase of Nl amplitude, as well as delayed P2, N2 and P3a latencies and lower amplitude of non-target P3a, correlated with indices of omissions and errors. However, an increase of P3a correlated with relatively shorter reaction time. Those results confirm earlier data related to smaller sample and imply an occurrence of either pathological or compensatory mechanisms on higher level of processing in face of primary disturbances on lower, automatic stage.

446 IMPAIRED SCHIZOPHRENIC

VISUAL SUBTYPES

PROCESSING

IN

B. Van Sweden’*, F. Mesotten2, L. Crevits3 ‘Dept. Clin. Neurophysiol, ‘Dept. Psychiatry, Medical Centre St.-Jozef, Bilzen, B-3740 Belgium, 3Dept. Clin. Neurophysiol University Hospital Ghent, Belgium Topographic differences in flash (FEP) and pattern reversal (PREP) data are compared in paranoid (n = 381, disorganised (n = 23) and residual (n = 23) schizophrenia. The P, generated over the occipito-temporal regions reflects the ventral information stream encompassing feature analysis and object recognition. Pattern identification is well preserved in paranoid and residual schizophrenia. The dorsal visual information stream in contrast involves spatial perception and visuomotor functions and is reflected in the N,,, generated over the occipito-parietal cortex. This response is intact in paranoid, but diminished and delayed in residual and disorganised schizophrenics. Normal FEP/PREP data concur with a well preserved global personality functioning in paranoid schizophrenia. Latency increase and amplitude decrease of the pattern Nu, concur with abnormal antisaccades documented in disorganised behaviour.

447 EYE TRACKING SCHIZOPHRENIA DURING PURSUIT MOVEMENTS

ABNORMALITIES IN FIXATION AND SMOOTH

J.K. Rybakowskit* , A. Borkowska2 ‘Department of Adult Psychiatry, University of Medical Sciences, Szpitalna 27/33 Str, Poznan, 60-572 Poland 2Department of Psychiatry, Medical Academy, Bydgoszcz, POland Purpose of study. Eye tracking abnormalities have been considered as neurophysiological markers of schizophrenia. A pathology of left cerebral hemisphere in this illness has been