The Effect of Lorazepam on the Silent Period of the Motor Evoked Potential

ABSTRACT

OBJECTIVE: The purpose of this study was to find out whether the duration of the silent period evoked by magnetic transcranial stimulation could be modulated by lorazepam. METHOD: Ten healthy volunteers were tested using the transcranial magnetic stimulation. Responses were recorded in the active abductor digiti minimi muscle, and baseline values were compared to the data obtained at 2 and 5 hours after administration of a single oral dose of 2.5 mg lorazepam. RESULTS: The motor threshold and size of the motor evoked potential remained unchanged after administration of lorazepam. The duration of cortical silent period was prolonged from 169.9+/-33.7 msec at baseline study to 248.1+/-50.4 msec at 2 hours and 248.5+/-47.3 msec at 5 hours after administration of the drug (p<0.01), but the peripheral silent period did not show any significant change. CONCLUSION: We have shown that the cortical silent period evoked by magnetic transcranial stimulation can be prolonged by administration of lorazepam. And the lack of effect on the motor threshold and on the size of the motor evoked potential after administration of lorazepam may indicate that these parameters are physiologically distinct from the cortical silent period. Therefore, prolonged cortical silent period may be resulted from the reinforcement of GABA action by lorazepam at the level of the motor cortex.