MEG gamma band activity in schizophrenia patients smd healthy subjects in a mental arithmetic task and at rest

Objectives: High Frequency oscillations have been suggested as a correlate of cognitive processes and have recently also been implicated in aberrant f orms of information processing. The present study investigated whether magn etoencephalographic (MEG) gamma band activity (20-71 Hz) can serve as an in dex of cognitive processes in the absence of external stimulation and to wh at extent gamma activity differs between healthy people and schizophrenia p atients. Methods: The amount and topography of MEG power in the gamma band range was examined in 15 schizophrenia patients and 15 healthy comparison subjects w hile performing a complex mental arithmetic task and at rest. Results: In healthy subjects a left frontal and left fronto-temporal increa se in gamma power was observed during mental arithmetic. Schizophrenia pati ents either failed to display such a task effect (30-45 Hz) or had reversed lateralization with enhanced activity over right frontal and right fronto- temporal regions under cognitive demands (45-71 Hz). In the frequency band from 60 to 71 Hz patients showed less gamma at fronto-temporal, posterio-te mporal and occipital sites irrespective of the task. Conclusions: These results indicate, first, that gamma topography can index cognitive activation in a very complex and purely internal task. Second, g roups differed in the pattern of activation during the task, a result which may be consistent with working memory dysfunction in schizophrenia. Third, the general topographic difference between healthy subjects and patients i s in line with the notion of abnormalities in the thalamocortical circuit i n schizophrenia. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved .