Neural basis of semantic priming in schizophrenia during a lexical decision task: a magneto-encephalography study.

Numerous behavioral and electrophysiological studies have provided evidence of abnormal semantic processing in schizophrenia. However, the neural basis of these deficits is poorly understood. We investigated magnetic cortical responses elicited by a word-pair lexical decision task in 20 patients with schizophrenia and 12 healthy control subjects. The task involved presentation of a prime word (200 ms), followed by a blank (250 ms), and then a target stimulus (1200 ms); the subject had to decide whether the target was a real word or not. During this task, bilateral temporal and left prefrontal activations were observed in both groups. However, in contrast to controls, patients with schizophrenia did not show increased activation in the left temporal and anterior cingulate cortices between 200 and 450 ms in response to semantic incongruity. These results suggested that schizophrenia was associated with a functional disturbance in some semantic regions that gave rise to the N400 component. Moreover, a significant modulation in the right temporal cortex was observed in patients, but not in controls. This suggested the existence of alternative processes in patients because both groups showed similar behavioral priming. Finally, we elucidated some functional abnormalities in the semantic network during prime word processing in patients, indicated by prolonged activation compared to healthy controls. Thus, in addition to context integration impairment, abnormal activations during the prime word provided new evidence of context processing deficits in schizophrenia.