ALTERED EXCITABILITY OF THE MOTOR CORTEX AFTER MINOR HEAD-INJURY REVEALED BY TRANSCRANIAL MAGNETIC STIMULATION

This study attempts to find out whether the motor evoked potential (ME P) elicited by single pulse and slow-rate (1 Hz) repetitive transcrani al magnetic stimulation (TMS) can disclose concealed subclinical impai rments in the cerebral motor system of patients with minor head injury . The motor response to single pulse TMS (STMS) of the patient group w as characterized by significantly higher threshold compared with that of the control group. The central motor conduction time, as well as th e peripheral conduction time were normal in all patients pointing to c ortical impairment. Two main patterns of MEP changes in response to re petitive TMS (RTMS) were observed in the patient group. A. - progressi ve decrease of the MEP amplitude throughout the stimulation session to a near complete abolition. B. - irregularity of the amplitude and the waveform of the MEP in a chaotic form. The MEP latency remained stabl e during the whole stimulation session. The MEP abnormalities recovere d gradually over the period of a few months. The higher threshold of t he motor response to STMS and the abnormal patterns of the MEP to RTMS seem to reflect transient impairment of cortical excitability or ''co rtical fatigue'' in patients who sustained minor head injures. Further study is needed to evaluated the extent and the pathophysiological me chanisms of the central nervous system fatigue phenomenon following he ad injury.