When aliens invade: multiple mechanisms for dissociation between will and action

The term alien hand sign was coined by Joseph Bogen to describe a curious wayward behaviour occasionally seen during recovery from transection of the corpus callosum.1 Such patients would react with surprise, concern, and perplexity at the capacity of their non-dominant hand to perform purposeful acts over which they felt no control. The term derived from an appellation originated by Brion and Jedynak—“le signe de la main étrangère”—describing behaviours seen in patients with callosal tumours.2 Although initially thought to be a problem affecting the non-dominant hand of patients with impaired callosal transmission, an identical problem affecting either the dominant or …