Atypical antipsychotics normalize low-gamma evoked oscillations in patients with schizophrenia

The symptoms of schizophrenia might be mediated by a cortical network disconnection which may disrupt the cortical oscillatory activity. Steady-state responses are an easy and consistent way to explore cortical oscillatory activity. A chirp-modulated tone (increasing the frequency of the modulation in a linear manner) allows a fast measure of the steady-state response to different modulation rates. With this approach, we studied the auditory steady-state responses in two groups of patients with schizophrenia (drug-naive and treated with atypical antipsychotic drugs), in order to assess the differences in their responses with respect to healthy subjects, and study any potential effect of medication. Drug-naive patients had reduced amplitude and inter-trial phase coherence of the response in the 30-50 Hz range, and reduced amplitude of the response in the 90-100 Hz range, when compared to controls. In the treated patients group, the response in the 30-50 Hz range was normalized to values similar to the control group, but the reduction in amplitude in the 90-100 Hz range remained as in the drug-naive group. These results suggest that gamma activity impairment in schizophrenia is a complex phenomenon that affects a wide band of frequencies and may be influenced by antipsychotic treatment.