Corticospinal excitability is specifically modulated by motor imagery: a magnetic stimulation study

Transcranial magnetic stimulation (TMS) was used to investigate whether the excitability of the corticospinal system is selectively affected by motor imagery. To this purpose, we performed two experiments. In the first one we recorded motor evoked potentials from right hand and arm muscles during me ntal simulation of flexion/extension movements of both distal and proximal joints. In the second experiment we applied magnetic stimulation to the rig ht and the left motor cortex of subjects while they were imagining opening or closing their right or their left hand. Motor evoked potentials (MEPs) w ere recorded from a hand muscle contralateral to the stimulated cortex. The results demonstrated that the excitability pattern during motor imagery dynamically mimics that occurring during movement execution. In addition, while magnetic stimulation of the left motor cortex revealed increased cort icospinal excitability when subjects imagined ipsilateral as well as contra lateral hand movements, the stimulation of the right motor cortex revealed a facilitatory effect induced by imagery of contralateral hand movements on ly. In conclusion, motor imagery is a high level process, which, however, m anifests itself in the activation of those same cortical circuits that are normally involved in movement execution. (C) 1999 Elsevier Science Ltd. All rights reserved.