Surround inhibition in motor execution and motor imagery

Surround inhibition (SI) is a neural mechanism to focus neuronal activity and facilitate selective motor execution (ME). The aim of the present study was to investigate whether SI is also generated during motor imagery (MI). Furthermore, we investigated whether the extent of SI during MI depends on the strength of SI during ME and/or vividness of MI. The extent of SI was examined during MI and ME of index finger flexion. Transcranial magnetic stimulation was applied at rest, during initiation of the movement (phasic phase) and during tonic muscle contraction of the index finger flexors. Motor evoked potentials (MEPs) were recorded from a surround muscle, abductor digiti minimi (ADM) and a synergistic muscle, the first dorsal interosseous muscle. The amplitude of ADM MEP was reduced during the phasic phase, which indicates that SI occurred during ME. In seven of 14 subjects, SI was also observed during MI, although this effect was not significant. There was a moderate correlation between the extent of SI during ME and MI. Furthermore, good imagers who experienced vivid MI during the MI task showed stronger SI than poor imagers. These results indicate that common neural substrates involved in SI during ME are at least in part recruited during MI. In clinical situations, the therapeutic use of MI to generate vivid MI may be one of effective tool to develop the strength of SI, which facilitate selective execution of desired movements.