Trancranial magnetic stimulation (TMS) provides a non-invasive means for exploring physiological alterations of central motor control in a variety of neuropsychiatric diseases. The present study aimed to assess the neurophysiological profile of muscle evoked responses to a standard TMS procedure in 51 medicated patients with schizophrenia and 51 age- and sex-matched healthy subjects. Motor evoked potentials (MEPs) from the abductor pollicis brevis muscle were elicited by stimulation of the contralateral motor cortex with a circular coil. The hot spot was marked, and the resting motor threshold (RMTh), the stimulus intensity for maximum MEP (SI-max), the post-stimulus silent period of voluntary muscle activity, and MEP latency and amplitude were measured. The main findings were the significantly higher than normal values for RMTh and SI-max, which are both indices of neuronal excitability. In particular, patients who had ziprasidone in their therapeutic regimen demonstrated the highest SI-max for both hemispheres, and the highest RMTh for the left hemisphere, patients receiving olanzapine demonstrated the lowest RMTh for the left hemisphere, and those on quetiapine showed intermediate values. The silent period was longer in the patients than in the controls when a RMTh-related SI was used and did not differ between the two groups when a fixed SI was used. We concluded that the observed TMS changes could be interpreted as primary alterations of intracortical motor excitability followed by defects of cortical inhibition and should be attributed to schizophrenia, antipsychotic medication or the interaction between the two factors.
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