Corticospinal facilitation during first and third person imagery

Motor imagery can be defined as the covert rehearsal of movement. Previous research with transcranial magnetic stimulation (TMS) has demonstrated that motor imagery increases the corticospinal excitability of the primary motor cortex in the area corresponding to the representation of the muscle involved in the imagined movement. This research, however, has been limited to imagery of oneself in motion. We extend the TMS research by contrasting first person imagery and third person imagery of index finger abduction-adduction movements. Motor evoked potentials were recorded from first dorsal interosseous (FDI) and abductor digiti minimi (ADM) during single pulse TMS. Participants performed first and third person motor imagery, visual imagery, and static imagery. Visual imagery involved non biological motion while static imagery involved a first person perspective of the unmoving hand. Relative to static imagery, excitability during imagined movement increased in FDI but not ADM. The facilitation in first person imagery adds to previous findings. A greater facilitation of MEPs recorded from FDI was found in third person imagery where the action was clearly attributable to another person. We interpret this novel result in the context of observed action and imagined observation of self action, and attribute the result to activation of mirror systems for matching the imagined action with an inner visuo-motor template.