Psychiatric Disorders and Electrophysiological Markers

Schizophrenia is considered as the most frequent and the most severe chronic psychotic disorder. Its evolutionary modes and its clinical symptomatology remain particularly heterogeneous. Moreover, the brain processes involved in schizophrenia are still far from being clearly understood. Current empirical studies provide a mean duration comprised between 1 and 3 years without any specific diagnosis or treatment. These diagnosis issues are partly based on difficulties in the early distinction between schizophrenia and bipolar affective disorders (BD).

These results emphasize the necessity of new early indices (or endophenotypes). Such markers are intended to be more specific than classical clinical manifestations. In other words, they have to be absent among patients with differential diagnosis, such as BD. Among other possible early indices, several electrophysiological disturbances have been explored.

Our study is designed to mainly describe the N400 component among patients with schizophrenia or BD. This component is classically interpreted as indexing the integration the meaning of a linguistic stimulus in its preceding context. Our main hypothesis aims to show a specific alteration of N400 component among patients with schizophrenia when compared to participants with BD.

The second aim of this study concerns the exploration of four other event related potentials (ERPs) among patients with schizophrenia or BD:

• the P50 component, involved in early sensory gating processes,
• the P300 component, thought to reflect attentional resource allocation and working memory updating of stimulus context,
• the P600 component, elicited during same paradigms than N400, and reflecting their syntactic congruity.
• the CNV (Contingent Negative Variation), reflecting processes of motor anticipation

Regarding to their potential 'endophenotypes' status, our aim consists in comparing the N400 and three other ERPs among patients with schizophrenia or bipolar affective disorder. Since the schizophrenic specificity of such ERPs alterations still remains rarely studied, we also propose to describe the possible relations between these ERPs results and clinical scores observed among patients.