Body schema and corporeal self-recognition in the alien hand syndrome

Objective: The alien hand syndrome (AHS) is a rare neuropsychological disorder characterized by involuntary,yet purposeful, hand movements. Patients with the AHS typically complain about a loss of agencyassociated with a feeling of estrangement for actions performed by the affected limb. The present studyexplores the integrity of the body representation in AHS, focusing on 2 main processes: multisensoryintegration and visual self-recognition of body parts. Three patients affected by AHS following a righthemispherestroke, with clinical symptoms akin to the posterior variant of AHS, were tested and theirperformance was compared with that of 18 age-matched healthy controls. Method: AHS patients and controlsunderwent 2 experimental tasks: a same-different visual matching task for body postures, which assessed theability of using your own body schema for encoding others' body postural changes (Experiment 1), and anexplicit self-hand recognition task, which assessed the ability to visually recognize your own hands (Experiment2). Results: As compared to controls, all AHS patients were unable to access a reliable multisensoryrepresentation of their alien hand and use it for decoding others' postural changes; however, they could relyon an efficient multisensory representation of their intact (ipsilesional) hand. Two AHS patients also presentedwith a specific impairment in the visual self-recognition of their alien hand, but normal recognition of theirintact hand. Conclusion: This evidence suggests that the AHS following a right-hemisphere stroke mayinvolve a disruption of the multisensory representation of the alien limb; instead, self-hand recognitionmechanisms may be spared.