Changes of intracortical inhibition during motor imagery in human subjects

Paired-pulse transcranial magnetic stimulation with a conditioning-test par adigm was used to assess changes of corticocortical inhibition and facilita tion during mental simulation of sequential finger movements in normal subj ects. The cortico-cortical inhibition (at interstimulus interval, ISI, of 3 ms) was significantly reduced in the relaxed opponens pollicis (OP) muscle during motor imagery, regardless of the absolute size of the test motor ev oked potential. The amount of cortico-cortical inhibition was similar to th at observed during a mild voluntary contraction of the OF. No change of cor tico-cortical facilitation was observed at the ISI of 12 ms. The data suppo rt the hypothesis that similar neural structures, including the primary mot or cortex, are activated during both mental simulation and actual execution of motor activities. (C) 1999 Elsevier Science Ireland Ltd. All rights res erved.