Am J Psychiatry 1997; 154:640-646
Copyright © 1997 by American Psychiatric Association
Aberrant semantic activation in schizophrenia: a neurophysiological study
PG Nestor, MO Kimble, BF O'Donnell, L Smith, M Niznikiewicz, ME Shenton and RW McCarley
Department of Psychiatry, Harvard Medical School, Boston, MA, USA.
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.
