Repetitive transcranial magnetic stimulation reveals abnormal plastic response to premotor cortex stimulation in schizophrenia

Background: Schizophrenia may be characterized by abnormal plastic modulation in cortical neuronal circuits. Activation of premotor cortex using repetitive transcranial magnetic stimulation (rTMS) produces suppression of cortical excitability in primary motor motor cortez. We hypothesized that premotor rTMS would cause less suppression of motor conical excitability in patients with schizopbrenia than in control subjects. Methods. Twelve patients diagnosed with schizophrenia and twelve healthy control subjects underwent subthresbold rTMS to the premotor area in a 15-min conditioning train. Measurements of primary motor conical excitability (motor evoked potential; MEP), the resting motor threshold (RMT), and cortical inhibition (Q) were taken before and after the rTMS. Results: There was no difference in RMT between groups at baseline, although the patient group bad less CI than the control group at baseline. Following rTMS, the change in both MEP size and RMT between groups was significant. After rTMS, MEP size was suppressed in the control group and increased in the patient group, whereas RMT increased in the normal control group and decreased in the patient group. Conclusions: Patients with schizopbrenia demonstrate abnormal brain responses to rTMS applied to the premotor cortex that appear to relate to reduced motor cortical inhibition.