Aberrant semantic activation in schizophrenia: a neurophysiological study

OBJECTIVE: Schizophrenia has long been thought to be characterized by a fundamental disturbance in semantic associations, which has often been presumed to be of neurobiological origin. The authors examined the neurophysiological characteristics of semantic processing in schizophrenic patients. METHOD: During EEG recording, 15 schizophrenic patients and 15 age-matched comparison subjects read sentences that had either sensible or nonsensical endings. The authors recorded the N400 component, a specific negative event-related brain potential occurring approximately 400 msec after the final word in the sentence. N400 is highly, if not uniquely, sensitive to semantic expectancy and context, and larger, more negative N400 amplitude is associated with increased semantic unexpectancy. RESULTS: In relation to the normal comparison subjects, the schizophrenic patients demonstrated prolonged N400 latency after nonsensical sentence endings and also showed enhanced N400 negativity, regardless of the sense of the sentence ending. CONCLUSIONS: These findings suggest slower and more diffuse semantic activation in patients with schizophrenia, perhaps reflective of a disease-related failure to maintain and to use semantic context.