An investigation of motor function in schizophrenia using transcranial magnetic stimulation of the motor cortex

Background. In this first investigation of motor function in schizophrenia using transcranial magnetic stimulation (TMS) the general hypothesis tested was that this methodology could be used to investigate the disruption of corticospinal inhibitory processes suggested by cognitive and psychophysiological paradigms. Method. Nine drug-free DSM-IV schizophrenic patients were compared with nine age- and sex-matched normal subjects. Electromyographic (EMG) recordings were made from the thenar muscles of the dominant hand during sustained, weak voluntary contraction. TMS over a particular threshold applied to the motor cortex would elicit a compound motor evoked potential (cMEP) followed by a period of suppression of EMG. Results. The latency of cMEPs following TMS was significantly shorter in the schizophrenic patients. The two groups did not differ significantly with respect to mean latency of suppression of EMG activity, or stimulus thresholds for either cMEPs or EMG suppression. Conclusion. These findings could be the result of a relative lack of corticospinal inhibition of motor responses; a change in the site of TMS activation; or an abnormality of peripheral nervous function in schizophrenia. Drug effects were unlikely since seven of the patients were drug-naive.