the recent-onset group (M=-2.53, SD=1.58) relative to the healthycomparison group (M=-3.97; SD=1.92). Consistent with Broc-khaus-Dumke et al's findings, the at-risk group'sMMNamplitudes atFz (M=-3.29; SD=1.49) were intermediate between those of thehealthy comparison group and the recent-onset group, but thosedifferences did not reach statistical significance (d=0.40).Discussion: We found robust and large effect size duration-deviantMMN deficits in recent-onset patients with schizophrenia. Indivi-duals at risk for developing schizophrenia showedmodest effect sizeMMN reductions relative to age-matched healthy comparisonsubjects. Future studies are needed to delineate the nature of MMNabnormalities early in the course of schizophrenia and to clarifywhether those deficits reflect premorbid neuropathology or ongoingdisease processes associated with illness progression.

doi:10.1016/j.schres.2010.02.647

Poster 153VISUAL EVENT-RELATED P3A FROM PASSIVE TASK IN PATIENTSWITH SCHIZOPHRENIA

Yang-Whan Jeon1, E-Jin Park1, Jung-Seo Yi2, Seung Hyun Kim3

1The Catholic University of Korea Seoul, Seoul, South Korea; 2HallymUniversity Seoul, Seoul, South Korea; 3Korea University Seoul, Seoul,South Korea

Background: The paradigm effects were not enough to beelucidated, even though it is well known that the event-relatedpotential P300 was useful for exploring schizophrenia. Most P300studies require the subject to actively respond to the targetstimulus, but P300-like waveforms also can be elicited with'passive' auditory paradigms in which an intentional discriminationbetween the two tones is not required.Methods: This study was designed to examine that visual passiveparadigm is appropriate for relatively uncooperative and admittedpatients with schizophrenia. Visual 3 stimulus oddball paradigm wasemployed for admitted patients with schizophrenia (N=50) andcontrols (N=35). For the patients, the symptoms severity wasassessed by Positive and negative syndrome scale (PANSS). Theparadigm was composed of standard (small circle, 80%), distractors(large rectangle, 10%), and targets (large circle, 10%) in a randommanner once every 2 s. The passive task was presented first, and thesubjectswere instructed to look at themonitor in relaxedmanner. Theactive task was presented in second session, and subjects were askedto press a mouse button to the targets. P3a to the distractors is elicitedin passive and active tasks. P3b to the targets is elicited in active task.Results: In active paradigm, the P3a and P3b were successfullyacquired in all 35 control subjects (100%), but in only 35 patients(75%). In passive paradigm, the P3a was elicited for 45 patients(90%) as well as for 35 control subjects (100%). Passive P3a (F=3.7,p=0.08 in amplitude, F=32, p<0.0001 in latency), active P3a(F=12.6, p=0.001 in amplitude, F=25, p<0.0001 in latency), andactive P3b (F=2.6, p=0.09 in amplitude, F=14.3, p<0.001)) weresmaller and delayed in patients with schizophrenia. With usingmixed between (groups) and within (anterior-posterior andlaterality) repeated measurement ANOVA, the P300 componentsshowed topographic differences between two groups (F=4.4,p=0.03 in passive P3a, F=5.7, p=0.001 in active P3a, andF=5.4, p=0.01 in active P3b).Discussion: Such a passive paradigm could be very interested, sinceit can be used with non-compliant subjects such as young children,individuals with demented illness, and difficult psychiatric patients.However, conventional visual stimuli presented under passiveviewing conditions can not elicit reliable P300 components because

the attentional demands of a visual target in an oddball sequenceare not compelling relative to the alerting qualities of an infrequentauditory target stimulus. Thus, passive and active paradigms canproduce P300 waveforms because component outcomes aredetermined by the eliciting stimuli if only when their physicalqualities coerce attentional engagement. The passive 3 stimulusvisual P300 paradigm could be used for further exploring thepatients with schizophrenia without or minimizing losing theinformation from some patients who are uncooperative with usingonly the conventional active P300 paradigms.

doi:10.1016/j.schres.2010.02.648

Poster 154N2 EVENT-RELATED POTENTIAL IN SCHIZOPHRENIA – DIFFUSIONIN TIME AND SPACE

Stefan Kaiser1,2, Mirjam Rentrop2, Alexander Roth3, KatlehnRodewald2, Joe Simon2, Stephan Walther2, Matthias Weisbrod2,4

1Psychiatric University Hospital, Zurich, Switzerland; 2Section ofExperimental Psychopathology, Department of General AdultPsychiatry, Centre for Psychosocial Medicine, Heidelberg, Germany;3Wilhelm-Schickard-Institute for Computer Science, Eberhard KarlsUniversity, Tübingen, Germany; 4SRH Klinikum Karlsbad-Langensteinbach, Germany

Background: Recent theories of schizophrenia have proposed afundamental instability of information processing on a neurophy-siological level. This instability can be measured as an increase inEEG noise or an increase in latency variability of event-relatedpotentials (ERPs). Another common observation is a more diffuseactivation of the prefrontal cortex on cognitive tasks, which isthought to reflect compensatory processes required due toinefficient processing. In the present study we examined temporalvariability as well as spatial distribution of the N2 component of thevisual ERP as an index of prefrontal cortical function.Methods: 28 patients with schizophrenia and 28 control partic-pants matched for gender, age and eduction participated in thestudy. Patients were stable patients recruited from a rehabilitationsetting with relatively preserved cognitive performance. Subjectsperformed a visual Go/Nogo task, while event-related potentialswere obtained. Trial-to-trial latency variability was calculated witha Wavelet-based method developed by our group (Roth et al., 2007,Int J Psychophysiology). Spatial distribution was assessed usingrepeated measures ANOVA across frontal electrodes.Results: On a behavioral level patients did not differ from controlparticipants on reaction time. There was trend-level impairment onoverall task performance in the Go-condition, but not in the Nogocondition. Patients with schizophrenia showed a reduced N2amplitude at midline electrodes. Importantly, patients with schizo-phrenia had increased N2 latency variability at electrodes Fz and Czin both task conditions (Go and Nogo). This increase in latencyvariability did not fully account for the amplitude reduction of theaverage ERPs. Regarding spatial distribution healthy participantsshowed a focused fronto-central N2 peak in both conditions. Incontrast, patients with schizophrenia showed a more diffusepattern with additional negative peaks over lateral electrodes.Discussion: These results clearly show that schizophrenia isassociated with higher temporal variability of ERPs as well as amore diffuse scalp distribution. The present study expands previousobservations by demonstrating these effects on the same ERPcomponent measure. This association suggests that the temporalvariability might index a fundamental instability of informationprocessing. Since there were few differences in task performance,

Abstracts366

the more diffuse spatial distribution might represent processescompensating for this temporal instability.

doi:10.1016/j.schres.2010.02.649

Poster 155DISTURBANCES IN EXECUTIVE CONTOL IN PATIENTS WITHSCHIZOPHRENIA

Menahem I. Krakowski1,2, Pierfillipo De Sanctis1, John Foxe1,31Nathan Kline Institute, Orangeburg, NY, USA; 2New York University,New York, NY, USA; 3Albert Einstein, Bronx, NY, USA

Background: Patients with schizophrenia have difficulties withexecutive control functions. It has been suggested that these deficitsin executive control are related to dysfunctional frontal and fronto-central activation patterns.Methods: This study investigated the cortical organization ofexecutive control in subjects with schizophrenia and healthycontrols using event-related potentials (ERPs). ERPs were collectedwhile subjects performed a visual Go/NoGo task which requiredthem to inhibit successfully during the NoGo trials the potentresponse tendency that was established by the frequent Go trials.ERPs were acquired from 64 scalp electrodes referenced to the noseand digitized at 512 Hz. Epochs of 900 ms were analyzed including100 ms pre-stimulus baseline. The interstimulus interval was1,000 ms. We compared the event-related brain potential (ERP)over the fronto-central scalp region (FCz) of 38 subjects with aDSM-IV diagnosis of schizophrenia and 23 matched healthy controlsubjects (18 -55 years of age).Results: There was a significant difference between the controlsubjects and the subjects with schizophrenia in correct rejectionaccuracy (t59=-2.4, p=.02). Therewas a 78% correct rejection rate inthe control subjects and a 57% rate in the subjects with schizophrenia.Event-related potentials revealed the neurophysiological substrate ofthis dysfunction. The N2 enhancement in response to successful NoGotrials relative to Go trials was used as a metric of successful inhibitorycontrol. There was a significant difference between the two groups inN2 peak amplitude (t59=-4.8, p<.0001), indicating a markeddifference in cortical activation during early processing. In the controlsubjects, there was a pronounced N2 component in the NoGo trials ascompared to the Go trials. This component was completely absent inthe subjects with schizophrenia. In the later stages of processing (P3time window), the P3 component was clearly present in theschizophrenic subjects, but it was still significantly less pronouncedthan in the control subjects (p<.05).Discussion: Schizophrenic patients performed worse than thecontrols when the button press was to withhold response, indicatinga failure of response inhibition. Both behavioral and ERP datademonstrate an impairment in executive control function in thesepatients. They exhibit deficient processing in a neuronal network infronto-central regions. This deficit is most prominent in the earlierstages of executive control function, but exists also in the later stages.

doi:10.1016/j.schres.2010.02.650

Poster 156THE MEDIAL PREFRONTAL AND ORBITOFRONTAL CORTICESINTERACT TO REGULATE NEURONAL ACTIVITY IN NUCLEUSACCUMBENS SUBREGIONS

Daniel J. LodgeUniv. Texas Hlth. Sci. Ctr. San Antonio, TX, USA

Background: Impairments in behavioral flexibility are consistentlyobserved in schizophrenia patients and likely result from adisruption in prefrontal cortical system function. The majorprefrontal regions implicated in schizophrenia are the medialprefrontal cortex (mPFC) and, to a lesser extent, the orbitofrontalcortex (OFC). These regions carry out independent, but comple-mentary forms of cognitive processing in changing environmentalconditions. It has been demonstrated that the prefrontal cortexprovides a topographic input to medium spiny neurons in thenucleus accumbens (NAc). The data presented here examines howafferents from the mPFC and OFC interact to regulate informationprocessing within individual NAc neurons.Methods: Male SD rats were anesthetized with chloral hydrate(400 mg/kg i.p.) and placed in a stereotaxic apparatus. Single unitevoked responses were recorded from neurons in the NAc core(AP: +1.5, L: +2.0, DV: -5.5-7.5) and shell (AP: +1.5, L:+1.0, DV:-5.5-7.5). Using concentric bipolar stimulating electrodes, alternat-ing single-current pulses (0.25 msec; 0.2-1.0 mA)were delivered at arate of 0.5 Hz to the OFC (AP:+3.0, L: +3.5, DV: -5.0) andmPFC (AP:+3.0, L: +0.5, DV: -5.0). Neurons receiving short latency(<25 msec), orthodromic, excitatory input from either the mPFC orOFC were examined.Results: Here we demonstrate that although the mPFC and OFCinnervate anatomically distinct sub-regions of the NAc, activitywithin these cortical regions is integrated to determine the outputof individual NAc neurons. Thus, neurons located in the NAc corepreferentially respond to activation of the OFC whereas neurons inthe shell subdivision were more likely to be activated by mPFCstimulation. Furthermore, the excitatory response to OFC stimula-tion in the NAc core was dramatically attenuated by pre-stimulation(10-40 msec prior) of the mPFC. Similarly, the OFC was also able toinhibit mPFC-evoked responses in the shell of the NAc, albeit in asmaller proportion of neurons. Finally, lidocaine inactivation of theOFC resulted in a significant increase in the response to mPFCstimulation in the NAc shell suggesting a tonic suppression of mPFCevoked activity.Discussion: Taken as a whole, these data demonstrate that the mPFCand OFC interact to negatively regulate evoked activity in the NAc andtherefore exist in a delicate state of balance with respect to theirinfluence on information processing within ventral striatal circuits.Such information is of relevance given the impairments in behavioralflexibility consistently observed in schizophrenia patients.

doi:10.1016/j.schres.2010.02.651

Poster 157CORTICAL THICKNESS DEFICITS AND GAMMA BAND OSCILATIONSIN SCHIZOPHRENIA

Sharmili Sritharan1,2, Christine Gruetzner1,2,Anna Rotarska-Jagiela1,2, Wolf Singer1,3, Peter J. Uhlhaas1,21Max-Planck-Institute for Brain Research Frankfurt am Main, Hessen,Germany; 2Department of Psychiatry,Johann-Wolfgang-GoetheUniversity Frankfurt am Main, Hessen, Germany; 3Frankfurt Institute ofAdvanced Studies Frankfurt am Main, Hessen, Germany

Background: Synchronisation of oscillatory activity provides apossible mechanism for the communication within and betweencortical areas of the brain. There is increasing evidence that theimpairment of this mechanism may contribute to the functionaldisconnectivity of cortical networks that underlies the profoundcognitive deficits and symptoms associated with schizophrenia. Therelationship to the underlying anatomical abnormalities, however,are still unclear. The current study aimed to examine the relation-

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