Hemisphere-specific effects of mirror box-induced disownership on corticomotor excitability

Body ownership refers to the feeling that the body belongs to oneself. This sense could be manipulated using the mirror box illusion (MBI), which modulates somatosensory processing. However, whether alterations in body ownership influence motor processing remains unclear. Therefore, we aimed to investigate the hemisphere-specific effects of altered body ownership on corticomotor excitability using transcranial magnetic stimulation (TMS).

Twenty healthy participants were enrolled. A mirror box was used to modulate the sense of body ownership. Participants observed the mirror reflection of either their right or left hand and tapped both index fingers either synchronously or asynchronously across a 15.2-cm gap for 60 sec. Their actual finger on the reflected side was obscured with a cardboard and cloth. Motor-evoked potentials (MEPs) were elicited from the first dorsal interosseous muscle of the hidden hand using TMS over the right or left primary motor cortex (M1). Changes in body ownership were assessed using the vividness of illusion (VI) and proprioceptive drift.

MEP amplitudes increased after synchronous tapping compared with those after asynchronous tapping in the right hand (left M1 stimulation), with no such effect in the left hand. The VI score and proprioceptive drift were greater after synchronous tapping but did not differ between hands.

Participants perceived their hands as closer to the mirror than their actual position, regardless of side. Mirror box-induced disownership produced a hemisphere-specific modulation of corticomotor excitability, suggesting that altered body ownership influences motor output in a lateralized manner.