ing the nature of P50 component. We manipulated stimulus fre-quency bands in auditory stimuli in order to investigate the natureof P50 in human auditory evoked potentials. Two paradigms havebeen used to obtain P50: one is a conditioning/testing paradigm inwhich paired of pure tone (1000 Hz) are delivered, and the otherwas presented paired of clicks, both with an intensity of 60 dbsound pressure level above the auditory threshold. A total of 30healthy volunteers were recruited for this study among center ofgenetic engineering (fifteen man and fifteen women, mean age of36.5), all without consumption of caffeine, cigarettes and drugs.No statistically significant differences occurred between the P50Amplitudes and latencies for the pure tone and those for theclicks. Our present results indicate that P50 in humans may reflecta feed-forward mechanism of the brain where a preceding stimu-lus drives Sensory gating mechanisms in preparation for a secondstimulus, but the contained frequencies doesn’t influence on theP50 component. Both types (tones or clicks) can be used in theexploration of patient with this evoked potential.

doi:10.1016/j.clinph.2008.04.266

251. Stop signal task to evaluate inhibition in Parkinson

Disease—E. Casabona, L. Alvarez, I. Pedroso, M.L.

Bringas Vega (Cuba)

This work purposes to characterize the inhibition response inpatients with Parkinson Disease (PD). Forty patients with PDand 40 normal subjects (controls) as closely as possible withregard to age, sex and years of education. All PD patients werereceiving medication during time of testing. The Stop-Signal taskinvolved a simple choice reaction time task (RT GO) during thediscrimination of left and right arrows on the screen of the com-puter. A stop signal (tone 1000 Hz) was presented on 25% of thetrials and the subject must stop the action, and the time employedto make the right inhibition was the SSRT (stop signal reactiontime). We found a significantly longer RT (GO) in PD patientscompared to the control group (PD: 884.1 mseg. Control: 297.7mseg P < 0.000001). Patients with PD did show an impairmentin response inhibition (SSRT P < 0.00003) than the controlgroup, also an expected deficit in response initiation. PD patientsshowed slowness in inhibition tasks The Stop-Signal paradigm isuseful to evaluate inhibition in PD patients.

doi:10.1016/j.clinph.2008.04.267

252. Asymmetries in the modulation of alpha-band power for

high attentional load conditions: Involvement of the atten-

tional control mechanism—A. Perez, E. Martınez Montes,

P.V. Peers, L. Galan, L. Garcıa, M. Valdes Sosa (Cuba)

This work purposes to examine whether the shifts in attentionreflect changes in attentional control or expression mechanisms.In a dual task paradigm with detection task followed after280 ms with a TOJ we examine oscillatory brain activity in thealfa-band. This biasing of the residual attention was associatedwith a decrease (desynchronization) of alpha-band activity overthe left side of the head and an increase (synchronization) ofalpha-band over the right side of the head, specifically at the T4

Electrode. The latter changes occurred before the TOJ task andeven in absence of it. A bias towards detecting right sided targetsas appearing first in the Temporal order judgment task (T2) wasseen when participants were made to detect the initial target. ThisEffect was associated with decreased alpha-band activity over theleft side of the head and increased alpha-band activity over theright, which were observable prior to the onset, and even in theabsence of T2. We argue that this lateralized activity suggests thatrightward shifts in attention may reflect reduced attention controlunder conditions of high load. The development of robust para-digms to assess the relationship between spatial and non-spatialaspects of attentional processing in healthy subjects, therefore,is of considerable importance in allowing us to go on understandthe relationship between spatial and non-spatial aspects ofattention.

doi:10.1016/j.clinph.2008.04.268

253. Perception of emotion and P300 event related potential

in schizophrenic patients and relatives—A. Reyes Berazaın,

M. Martın Reyes, S. Guerra, R. Mendoza Quinonez, M.

Domınguez, T.M. Bravo, M. Valdes Sosa (Cuba)

Schizophrenia is characterized by a global cognitive impair-ment, with varying degrees of deficits. Since genetic factors areimportant in the etiology of the illness, we investigated whetherrelatives of the schizophrenic patients also show cognitive deficits.In the present study we used the P300 event relative potential toexamine the processing of facial emotion recognition in schizo-phrenic patients (N = 27) and first degree relatives (N = 30) andhealth adult subject (N = 74). Study subjects were instructed torespond to a specific target. We used three facial emotion expres-sions, (neutral, happiness and fear). The identification of negativeemotion was poorly in patients than in control. The amplitude ofP300 was reduced for fear and happy in schizophrenic patientsand relatives when comparing to controls. This finding are in linewith neurobehavioral studies, schizophrenic patients showedgreater impairment in the recognition of negative emotions.

doi:10.1016/j.clinph.2008.04.269

254. P50 evoked potential in the behavioral exploration ofepileptic patients under cetogenic diet management—L.A.

Perez, S. Guerra, M.A. Pedroso, M.E. Rizo (Cuba)

Evaluation with P50 evoked potential of the behavioralchanges occurred in children with refractive epilepsies who weretreated with cetogenic diet. Three epileptic children with LennoxGastaut syndrome were studied with classical paradigm condi-tioning/test. We used a stimulus a clicks, which was producedby a square pulse of 0.4 ms. We evaluated the amplitude andlatencies of the obtained answers to the S1 (conditional stimulus)and S2 (test stimulus) previous to treatment and to the threemonths to beginning the dietetic management. We also exploredthe percent of suppression of P50 [1-(Amplitude S2/S1) � 100].And these results are correlated with the behavioral changes ina scale of life quality. A mean comparison test showed significantdifferences in the Percent of suppression of the P50, before and

Society Proceedings / Clinical Neurophysiology 119 (2008) e99–e164 e161