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EN
The effect of stress induced by the novelty of a situation was evaluated by means of event-related potentials (ERPs). Potentials, recorded with Fz, Cz and Pz electrodes, were evoked by flashing red and yellow LED diodes. A standard 'odd ball' procedure was used, in which flashes of one color were mentally counted (target stimuli). ERPs evoked by target and non-target stimuli recorded in the first session of the experiment were compared with those recorded at least 40 min later. The early waves and P200 components indicated the increased responsiveness during the initial sessions. Amplitudes of both components were significantly larger. Latencies of the early waves were also significantly shorter. The effects were present in responses to both target and non-target stimuli. In contrast, the latency of P300 wave was significantly elongated during the first recording. Grand-averaged curves indicated also a reduction of P300 amplitude, but when individual waves were analyzed, the effect did not reach the level of statistical significance. It was suggested that the novel situation could be employed as a model of relatively pure stress, useful in the interpretation of other results such as the effects of pain.
EN
Correlations between measures of attention and topographical abnormalities of evoked cortical potentials elicited during the Continuous Attention Test (CAT) were assessed in 50 schizophrenic patients, compared to 50 healthy subjects. For each group and for each CAT condition evoked responses consisted of six successive epochs (segments) of stable spatially configured potentials. Quantitative descriptors of those configurations (Lehmann 1987) were referred to the CAT data. In patients: (1) segments III-V were delayed, (2) in the non-target condition, diminished global field power (GFP) emerged, coexisting either with lower amplitude of posterior potentials in segment I and II or with lower amplitude of a central positive potential in segment V, (3) an altered topographic pattern of responses to the target stimulus occurred. In healthy subjects detection of the target (as compared to the non-target condition) was associated with a shift of the location of the positive potential in segments IV and V from a central towards the prefrontal area. In patients, in segment V a similar shift reached frontal, but not prefrontal areas, and additionally, the central areas remained active. Delayed latency and low GFP in segment V in the non-target condition in patients correlated with poor CAT performance. A more posterior location of the positive centroid in segment V during detection of the target correlated with better CAT results, and the associated GFP increase with less prolonged reaction time. The data revealed a possible compensatory role of central and frontal areas in the face of weakened prefrontal functions in schizophrenia.
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