The mirror world of motor inhibition: the alien hand syndrome in chronic stroke

Abstract

Alien hand syndrome (AHS) is rare, but important due to its disabling impact on everyday life. The determining characteristic of AHS is intermanual conflict, a type of inhibitory motor behaviour that occurs against willed action. Its components have previously been described as single case reports, but not as a systematic study. This review includes eight chronic cases, all of which are due to infarcts of the anterior cerebral artery. Clinical investigation included testing of motor behaviour related to everyday activities, such as tying shoelaces, lighting a candle and other bimanual tasks. Video-analysis showed that conflicting behaviour occurs in two distinct forms. One consists of interfering, rudimentary, hesitant and repetitive movements of the (alien) hand, often initiated by movements of the other hand. In some instances, disturbance of ongoing action is seen as spacious, ballistic-like extensions of the whole arm. This was most prevalent in three of the eight cases. In one patient, it was also seen as conflict with both feet (eg, when putting on slippers) or as a conflict of intentions (eg, when planning to enter a room). The other form consisted of massive groping and grasping behaviour as the most dominant features, such as a "tug of war between hands", and was seen in five patients. Avoidance behaviour included sitting on the affected arm, holding it under the table or keeping objects out of reach. Enforcement of such strategies was used for rehabilitation and--although beneficial in the training sessions--carried over very little to everyday life. All cases had two distinct brain lesions, one in the genu or anterior rostrum of the corpus callosum and one in the contralateral frontomedial cortical and subcortical region. Chronic AHS is the only clinical syndrome that shows complex inhibitory motor behaviour in a more or less pure form because it has become detached from the control of motor planning and execution. It can best be understood as sequences of complex inhibitory motor programmes that have become isolated from normal motor planning, which usually suppresses them via the contralateral cortico-subcortical prefrontal circuits and the corpus callosum. Thus, the mirror world of complex motor inhibition becomes clinically visible in such patients.