CORTICAL OUTPUT MODULATION AFTER RAPID REPETITIVE MOVEMENTS

Transcranial magnetic stimulation was used to evaluate changes in moto r cortex excitability after rapid repetitive movements in five healthy subjects aged 23-30 years, by considering the amplitude of motor evok ed potentials (MEPs) at rest and after one minute of maximal frequency repetitive abduction-adduction movements of the thumb. In addition, M and F waves were evaluated by stimulating the median nerve at the wri st. All of the examined subjects showed a clear modification in post-e xercise MEP amplitudes, with a mean maximal reduction of 50-60% in com parison with basal values and complete recovery after a period of abou t 35 minutes. The time course of this phenomenon showed a triphasic pa ttern: (I) a rapid decrease phase up to the fifth minute; (II) a maxim al depression phase for a period of about ten minutes; (III) a slow re turn to basal values. No significant changes were observed in post-exe rcise M and F waves. These results show the existence of a reversible modulation of the excitability of the upper motor neuron after rapid r epetitive movements. It is likely that this modulation takes place at the level of the motor cortex and that its anatomofunctional substrate is represented by the activation of inhibitory intracortical circuits .