A Moving Discovery
In 1908, eminent German neuropsychiatrist Kurt Goldstein saw a patient who complained of involuntary movements of her left hand shortly after suffering from a stroke (Sarva, H., Deik, A., & Severt, W. L., 2014). Goldstein observed the unusual nature of the uncontrollable and repetitive grasping movements made by the patient. The movements which the patient experienced took place entirely without her control, and thus left the patient with an overwhelming sense of having her left arm belonging to another person. Suffering from not knowing the cause of her misery, the patient exclaimed “There must be an evil spirit in the hand!” While this of course was not true, there was still reason for genuine confusion given the disorder was then unknown (Mark, V. W., n.d.). Eventually, though, this curious phenomenon was named “alien hand” syndrome (AHS) in a study that was conducted on the disorder in 1972 (Brion, & Jedynak.,1972). Today, scientists know that AHS is the result of injury to the brain in a number of different regions and that the disorder occurs most often in patients who previously suffered from other conditions such as stroke or brain tumors.
The most prominent feature of AHS is the loss of sense of agency, or being consciously aware of moving a specific body part. The loss of volition results in the experienced autonomy of the affected “alien” body part. While AHS covers a broad spectrum of involuntary hand movements that can sometimes be accompanied with a loss of sensory processing known as agnosia, there are three primary variants that stem from neural damage that the majority of patients have. The first of these forms of AHS is known as the anterior variant and is caused by lesions of a number of brain regions, most notably the corpus callosum, or the part of the brain which connects the left and right cerebral hemispheres through its 200 million axonal nerve fibers. (Hubel, D., n.d.). In this type, the patient will experience the alien hand unilaterally in their non-dominant hand. Another variation, known as the posterior variant, is the product of damage to the thalamus, the parietal lobe, and occipital lobes. In this form, patients withdraw their affected hand from physical contact with others when an object or a person gets near to them and nearly touches their hand. Additionally, some patients may experience involuntary hand levitation. The other main type of AHS is the callosal variant. This form is very similar to the anterior variant, but differs in that it can only be caused by damage to the corpus callosum. Patients with the callosal variant often experience intermanual conflict, or the involuntary opposition to voluntary movements of the unaffected hand by the affected alien hand. The callosal variant is the type of AHS in which it is common to see the hands of a patient fighting each other. In short, the frontal (anterior) variant causes unconscious purposeful actions such as grasping, the callosal variant produces intermanual conflict and the posterior variant primarily results in involuntary hand levitation. (Sarva, H., Deik, A., & Severt, W. L., 2014)
Although the different variants of AHS each have their own unique causes and pathologies, the cause of the syndrome as a whole can be defined as the damage to a specific brain area that results in abnormal sense of agency with a hand. Within this inclusive definition are a broad array of separate diseases that can onset the condition by evoking the initial insult to the brain. A number of ordinary causes which have been documented to cause AHS include anterior cerebral artery strokes, neurodegenerative diseases and midline tumors. Brain damage causes disruption of networks which may result in the loss of inhibition of neural activity responsible for the symptoms that AHS patients experience (Sarva, H., Deik, A., & Severt, W. L., 2014).
Currently, there is no cure or approved treatment for any of the three variants of AHS. Many therapies can aid in the reduction of how AHS disrupts the life of a patient, but no methods are able to completely stop the alien movements. Some of the therapies are aimed toward providing coping mechanisms to lessen the severity of the condition, while others focus more on distractions to dampen down the syndrome (Sarva, H., Deik, A., & Severt, W. L., 2014). Benzodiazepines such as clonazepam have been used to treat patients, but they have been less effective than behavioral modification therapies and are thus not widely used.
Volition- the ability of choosing to do something
Agnosia- loss of sensory processing and interpretation
Anterior variant- type of AHS associated with involuntary purposeful actions
Corpus callosum- bundle of nerve fibers bridging the two cerebral hemispheres
Posterior variant - type of AHS associated with involuntary hand levitation
Thalamus - the part of the brain involved in processing received sensory information
Parietal lobe - brain lobe whose main functions are sensory processes, attention and language
Occipital lobe- brain lobe responsible for visual perception
Callosal variant- type of AHS associated with intermanual conflict
Intermanual conflict - movement of the alien hand that interferes with non-affected hand
Sense of agency- the awareness of initiating and controlling movements
Benzodiazepines- class of drugs that increase the activity of the neurotransmitter GABA
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