EFFECTS OF DIAZEPAM, BACLOFEN AND THIOPENTAL ON THE SILENT PERIOD EVOKED BY TRANSCRANIAL MAGNETIC STIMULATION IN HUMANS

The cortical silent period evoked by magnetic transcranial stimulation and the peripheral silent period were studied in healthy subjects aft er intravenous injection of diazepam, baclofen or thiopental. None of the drugs tested changed the peripheral silent period. But, unexpected ly, diazepam significantly shortened the cortical silent period, the i nhibitory effect lasting about 30 min. In experiments using paired tra nscranial stimuli, the conditioning shock inhibited the test response to a similar extent with and without diazepam. Although baclofen did n ot change the cortical silent period, it reduced the size of the H ref lex in the forearm muscles. Thiopental also left the duration of the c ortical silent period unchanged. These findings show that the cortical silent period can be modified pharmacologically. Diazepam possibly sh ortens the silent period by modulating GABA A receptors at a subcortic al site.