Spontaneous gamma coherence as a possible trait marker of schizophrenia-An explorative study

Integration of sensory information by cortical network binding appears to be crucially involved in sensory processing activity. Studies in schizophrenia using functional neuroimaging, event-related potentials and EEG coherence indicate an impairment of cortical network coupling in this disorder. Previous electrophysiological investigations in animals and humans suggested that gamma activity (oscillations at around 30-100Hz) is essential for cortical network binding. This is the first investigation of spontaneous gamma activity in schizophrenics and their first degree relatives as compared to normal controls.

Resting EEG was recorded in 20 drug naïve/drug free male schizophrenic patients, their pair matched male first degree relatives and 20 age-, sex-, education- and handedness-matched normal controls. Power spectrum and coherence of gamma band activity was analysed using MATLAB 6.5.

Schizophrenic patients had significantly less interhemispheric spontaneous gamma coherence and increased gamma power compared to normal controls. But there was no significant difference in gamma coherence between patients and their first degree relatives. Spontaneous gamma coherence had significant correlation with few PANSS subscale scores.

There is cortical hyperactivation and a reduced spontaneous and induced gamma coherence abnormality in schizophrenia. The abnormal gamma coherence appears explaining the psychopathology and poor performance on cognitive task in schizophrenia. This study has also generated hypotheses that the gamma band abnormality may be a trait abnormality in schizophrenics as seen by the similarity between the patient and their clinically asymptomatic first degree relatives.