CHANGES IN HUMAN MOTOR CORTEX EXCITABILITY INDUCED BY DOPAMINERGIC AND ANTIDOPAMINERGIC DRUGS

Transcranial magnetic stimulation was used to probe the acute effect o f a single oral dose of various dopaminergic (levodopa, selegiline, br omocriptine) and antidopaminergic drugs (sulpiride, haloperidol) on mo tor cortex excitability in healthy volunteers. Motor threshold, intrac ortical inhibition and intracortical facilitation were tested in the a bductor digiti minimi muscle. The latter two parameters were studied i n a conditioning-test paired stimulus paradigm. The principal findings were an increase in intracortical inhibition by bromocriptine, and, c onversely, a decrease in intracortical inhibition and an increase in i ntracortical facilitation by haloperidol. Effects peaked at delays con sistent with the pharmacokinetics of the two drugs and were fully reve rsible. In conclusion, dopamine receptor agonists and antagonists can be considered inverse modulators of motor cortex excitability: the for mer enhance inhibition while the latter reduce it. The relation of the present findings to current models of motor excitability abnormalitie s in movement disorders will be discussed. (C) 1997 Elsevier Science I reland Ltd.