Awareness of somatic events associated with a voluntary action.

How does the brain distinguish actions that we perform from movements imposed on us? To study links between the representations of actions and their somatosensory consequences, we compared the perceived times of voluntary actions or involuntary movements and of a subsequent somatic effect (a TMS-induced twitch of the right index finger). Participants perceived voluntary actions as occurring later and their bodily effects as occurring earlier in the agency context, compared to single-event baseline conditions. When the voluntary action was replaced by a passive, involuntary movement this attraction effect reversed. In a second experiment, subjects rated the intensity of the same TMS-induced somatic effect, again following a voluntary action or a passive movement. When the somatic effect was caused by a voluntary action, it was perceived as significantly less intense than when it followed a passive movement. Our results suggest a binding mechanism integrating awareness of somatic consequences occurring in voluntary action. This 'intentional binding' mechanism might underlie the way in which the mind constructs a strong association between intentions, actions and consequences so as to generate the unique and private phenomenological experience of self-agency.