Alien motor phenomena: a window on to agency.
BACKGROUND
Alien motor phenomena arise in neurological and psychiatric contexts and are likely to implicate several distributed brain systems.


METHODS
A selective literature review, focusing on cognitive neurobiological accounts of alien/anarchic limb, somatoparaphrenia, and delusions of alien control (passivity phenomena); supplemented by an account of the cognitive neuroanatomy of action and agency (subjective sense of causation) in the normal state.


RESULTS
Alien motor phenomena reflect impairments of agency through at least two mechanisms. (1) A disinhibition of ''lower'' motor centres giving rise to relatively stereotypic and contextually inappropriate motor routines (as emerge following medial frontal and corpus callosal lesions). (2) A disturbance of the perception of self-initiated movement, so that control of movement (causation) is attributed to an alien entity (phenomena associated with right parietal lobe lesions, focal epilepsy, and hyperactivity in acute schizophrenia).


CONCLUSIONS
Whereas alien/anarchic limb dysfunction may be relatively easily explained in cognitive neurobiological terms, a comprehensive account of alien control will require further empirical ingenuity. Current models invoke disturbed feed-forward mechanisms, imitation, and the sense of another's agency (''nonself attribution'').
University of Sheffield, Academic Department of Psychiatry, The Longley Centre, UK. S.A.Spence@Sheffield.ac.uk
Sean A
SA
Spence