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Alien Hand Syndrome

Shashwat Goyal

Blog Post-1

Alien hand syndrome (aka Dr. Strangelove syndrome) is a disorder which causes movements in a person’s limbs independent of their will. The condition was first described by Goldstein in 1908 as “a type of apraxia with the feeling of estrangement between the patient and hand.” While this name can be used for a variety of conditions, most commonly occurring in the left hand. The movements can include complex motor functions such as reaching for, holding and manipulating objects or counteracting the actions of the controlled hand. Patients report having no control over the independent limb, often having no realization that one of their limbs is moving on its own. In the following paragraphs, I will be describing the most common variants of this syndrome, as well as explaining the neurological causes behind it (as understood currently).
The use of the term “alien hand” implies a somewhat different condition, as it requires the patient to feel the hand is a separate entity, one that they may assign personalities. Patients descriptions of such limbs range from “cheeky” to “monster from the moon”. One patient even named hers “baby Joseph” as it would often pinch her nipples, causing a sensation like the biting of a breast-feeding baby.
It’s most commonly seen in people who’ve had damage or surgery resulting in severing of the corpus callosum (structure that connects the two hemispheres of the brain). It is also reported in cases of stroke, infection, tumour, aneurysm, migraine, and degenerative brain diseases like Alzheimer’s and Creutzfeldt-Jakob. Other areas associated with this condition are frontal, parietal and occipital. The most common variants are the callosal and frontal lesions.
The callosal variant involves damage to the corpus callosum and affects the non-dominant hand. Patients of this variant commonly show “inter-manual conflict”, where the alien hand acts against the controlled hand, such as taking a cigarette (that the patient has put in their mouth using their controlled hand) out of the mouth and throwing it away. It is thought that there is a conscious agent in the dominant hemisphere of the brain. This agent links action to language encoded thought due to direct connection between the agency system and the encoding system in the dominant hemisphere. Since the actions committed by the non-dominant limb are often complex and purposeful, the idea that there is only one agent in the brain, present in the dominant hemisphere is rendered false. Hence, another subservient agent in the non-dominant hemisphere that is controlled by the conscious agent is theorized. When the corpus callosum is severed, thus subservient agent breaks free from the control of the dominant agent. While this theory does explain why the non-dominant hand is considered alien (as the sense of agency corresponding to its movement doesn’t develop or is inaccessible to the conscious agent) and why the alien hand shows complex actions, it fails to explain why the separate agent causes inter-manual conflict between the hands.
The frontal variant involves damage to the frontal lobe and usually affects the dominant hand, but can affect any hand based on the localization of the damage to the medial frontal cortex. This variant causes grasp reflexes, reaching for objects and the inability to release grasp (tonic grasping). Brain scans such as fMRIs have been used to try and determine the neurological cause of this disorder. These tests revealed that any voluntary movement and the sense of agency associated with it is caused by a decided order of “anterior to posterior” activation of brain areas, from supplementary and premotor areas like (anteromedial frontal cortex) to the primary motor cortex in the pre-central gyrus and then to the posterior parietal cortex. The primary motor cortex is believed to be directly involved in executing the action while the signal sent to the parietal lobe is an efferent copy that interacts with and cancels out the somatosensory feedback that the periphery sends to the brain as a result of movement. Thus the feedback from the periphery is perceived as re-afference (due to self-generated movement) and not as ex-afference (due to external stimuli). Damage to the brain can result in direct activation of the primary motor cortex, leading to the execution of an action without the sending of an efferent copy to the parietal lobe. Hence, a directly activating primary motor complex without the premotor and supplementary motor areas can cause a feeling of a limb moving of its own accord rather than by an internally generated signal, as is actually the case. The sense of ownership of the arm seems unaffected by this loss of sense of agency, and the cognitive dissonance created by the occurrence of movement without a physical external stimuli or a sense of agency in the patient is resolved by assigning the agency to the arm itself and treating it as a separate, external entity or an alien.


References

1)     Wikipedia page for alien hand syndrome
2)     https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3438424/
3)     https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5155497/

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