The alien hand syndrome (AHS) is rare but an important entity because of its disabling impact on everyday life. The hallmark is the intermanual conflict, a type of inhibitory motor behaviour directed against willed action. Its components have previously been described as single case reports but not as a systematic study. This series includes eight chronic cases, all of them due to infarcts of the anterior cerebral artery. Clinical investigation included testing of motor behaviour related to everyday activities such as tying shoelaces, lightening a candle and other bimanual tasks. Video-analysis showed that conflicting behaviour consists of a spectrum between two distinct forms. One consists either of 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 (e.g. when putting on slippers) or as conflict of intentions (e.g. 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 which 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 where they usually are suppressed 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.
- alien hand syndrome
- hemispheric disconnection
- ideomotor apraxia
- limb apraxia
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