Gamma activity in schizophrenia: evidence of impaired network binding?

Objectives: Gamma ('40 Hz') rhythms may play a role in the integration of s ensory processing activity. Impaired temporal integration may be a key feat ure of the associated disturbances in schizophrenia. This is the first stud y to examine the time course of Gamma activity induced in response to stimu li in this disorder. Methods: Gamma activity induced in response to task-relevant and irrelevant auditory oddball stimuli was examined in 35 medicated schizophrenics and 3 5 age- and gender-matched normal controls. We employed a moving Welch windo w with short time FFT to examine the time course of Gamma amplitude. The am plitude spectrum for each time point was de-trended to eliminate any contri bution of broad spectrum activity (EEG or EMG) to Gamma amplitude. Results: For targets, schizophrenics showed a significant decrease in post- stimulus Gamma response amplitude in left hemisphere and frontal sites and an increase in right hemisphere and parieto-occipital sites (P < 0.0009). T he abnormalities correlated with PANSS general symptom scores. In the non-t argets (at a different latency), schizophrenics showed a widespread Gamma d ecrease (P < 0.0005). Conclusions: The Gamma findings in non-targets may reflect an abnormality i n appropriately processing irrelevant stimuli. This could result in defecti ve processing of the context (integration) of relevant target information. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.