Alien hand syndrome (AHS) or alien limb syndrome is a category of conditions in which a person experiences their limbs acting seemingly on their own, without conscious control over the actions. There are a variety of clinical conditions that fall under this category, most commonly affecting the left hand. There are many similar terms for the various forms of the condition, but they are often used inappropriately. The affected person may sometimes reach for objects and manipulate them without wanting to do so, even to the point of having to use the controllable hand to restrain the alien hand. The occurrence of alien hand syndrome can be usefully conceptualized as a phenomenon reflecting a functional "disentanglement" between thought and action.
Alien hand syndrome is best documented in cases where a person has had the two hemispheres of their brain surgically separated, a procedure sometimes used to relieve the symptoms of extreme cases of epilepsy and epileptic psychosis, e.g., temporal lobe epilepsy. It also occurs in some cases after brain surgery, stroke, infection, tumor, aneurysm, migraine and specific degenerative brain conditions such as Alzheimer's disease, corticobasal degeneration and Creutzfeldt–Jakob disease. Other areas of the brain that are associated with alien hand syndrome are the frontal, occipital, and parietal lobes.
There are five different types of Alien Hand Syndrome. Diagnostic Dyspraxia, where one hand acts independently from the other;Alien Hand Sign, where the person believes that the hand is not their own; Anarchic Hand Syndrome, where the hand performs a task that the person has no control over; Supernumerary Hand, where the person feels that they have an extra limb; and Levitating Hand, where the hand rises on its own.
Signs and symptoms "Alien behavior" can be distinguished from reflexive behavior in that the former is flexibly purposive while the latter is obligatory. Sometimes the affected person will not be aware of what the alien hand is doing until it is brought to their attention, or until the hand does something that draws their attention to its behavior. There is a clear distinction between the behaviors of the two hands in which the affected hand is viewed as "wayward" and sometimes "disobedient" and generally out of the realm of their own voluntary control, while the unaffected hand is under normal volitional control. At times, particularly in individuals who have sustained damage to the corpus callosum that connects the two cerebral hemispheres , the hands appear to be acting in opposition to each other.
A related syndrome described by the French neurologist François Lhermitte involves the release through disinhibition of a tendency to compulsively utilize objects that present themselves in the surrounding environment around the patient. The behavior of the patient is, in a sense, obligatorily linked to the "affordances" (using terminology introduced by the American ecological psychologist, James J. Gibson) presented by objects that are located within the immediate peri-personal environment.
This condition is known as utilization behavior. It is most often associated with extensive bilateral frontal lobe damage and might actually be thought of as "bilateral" alien hand syndrome in which the patient is compulsively directed by external environmental contingencies (such as the presence of a hairbrush on the table in front of them elicits the act of brushing the hair) and has no capacity to "hold back" and inhibit pre-potent motor programs that are obligatorily linked to the presence of specific external objects in the peri-personal space of the patient. When the frontal lobe damage is bilateral and generally more extensive, the patient completely loses the ability to act in a self-directed manner and becomes totally dependent upon the surrounding environmental indicators to guide their behavior in a general social context, a condition referred to as "environmental dependency syndrome".
To deal with the alien hand, some individuals engage in personification of the affected hand. Usually these names are negative in nature, from mild such as "cheeky" to malicious "monster from the moon". For example, Rachelle Doody and Jankovic described a patient who named her alien hand "baby Joseph". When the hand engaged in playful, troublesome activities such as pinching her nipples (akin to biting while nursing), she would experience amusement and would instruct baby Joseph to "stop being naughty". Furthermore, Bogen suggested that certain personality characteristics, such as a flamboyant personality, contribute to frequent personification of the affected hand.
Neuroimaging and pathological research shows that lesions of the frontal lobe (in the frontal variant) and corpus callosum (in the callosal variant) are the most common anatomical lesions responsible for the alien hand syndrome. These areas are closely linked in terms of motor planning and its final pathways.
The callosal variant includes advanced willed motor acts by the non-dominant hand, where individuals frequently exhibit "intermanual conflict" in which one hand acts at cross-purposes with the other "good hand". For example, one patient was observed putting a cigarette into her mouth with her intact, "controlled" hand (her right, dominant hand), following which her left hand rose, grasped the cigarette, pulled it out of her mouth, and tossed it away before it could be lit by the right hand. The patient then surmised that "I guess 'he' doesn't want me to smoke that cigarette." Another patient was observed to be buttoning up her blouse with her controlled dominant hand while the alien non-dominant hand, at the same time, was unbuttoning her blouse. The frontal variant most often affects the dominant hand, but can affect either hand depending on the lateralization of the damage to medial frontal cortex, and includes grasp reflex, impulsive groping toward objects or/and tonic grasping (in other words, difficulty in releasing grip).
In most cases, classic alien-hand signs derive from damage to the medial frontal cortex, accompanying damage to the corpus callosum. In these individuals, the main cause of damage is unilateral or bilateral infarction of cortex in the territory supplied by the anterior cerebral artery or associated arteries. Oxygenated blood is supplied by the anterior cerebral artery to most medial portions of the frontal lobes and to the anterior two-thirds of the corpus callosum, and infarction may consequently result in damage to multiple adjacent locations in the brain in the supplied territory. As the medial frontal lobe damage is often linked to lesions of the corpus callosum, frontal variant cases may also present with callosal form signs. Cases of damage restricted to the callosum however, tend not to show frontal alien-hand signs.
Cause The common emerging factor in alien hand syndrome is that the primary motor cortex controlling hand movement is isolated from premotor cortex influences but remains generally intact in its ability to execute movements of the hand.
A 2009 fMRI study looking at the temporal sequence of activation of components of a cortical network associated with voluntary movement in normal individuals demonstrated "an anterior-to-posterior temporal gradient of activity from supplemental motor area through premotor and motor cortices to the posterior parietal cortex". Therefore, with normal voluntary movement, the emergent sense of agency appears to be associated with an orderly sequence of activation that develops initially in the anteromedial frontal cortex in the vicinity of the supplementary motor complex on the medial surface of the frontal aspect of the hemisphere (including the supplementary motor area) prior to activation of the primary motor cortex in the pre-central gyrus on the lateral aspect of the hemisphere, when the hand movement is being generated. Activation of the primary motor cortex, presumed to be directly involved in the execution of the action via projections into the corticospinal component of the pyramidal tracts, is then followed by activation of the posterior parietal cortex, possibly related to the receipt of recurrent or re-afferent somatosensory feedback generated from the periphery by the movement which would normally interact with the efference copy transmitted from primary motor cortex to permit the movement to be recognized as self-generated rather than imposed by an external force. That is, the efference copy allows the recurrent afferent somatosensory flow from the periphery associated with the self-generated movement to be recognized as re-afference as distinct from ex-afference. Failure of this mechanism may lead to a failure to distinguish between self-generated and externally generated movement of the limb. This anomalous situation in which re-afference from a self-generated movement is mistakenly registered as ex-afference due to a failure to generate and successfully transmit an efference copy to sensory cortex, could readily lead to the interpretation that what is in actuality a self-generated movement has been produced by an external force as a result of the failure to develop a sense of agency in association with emergence of the self-generated movement (see below for a more detailed discussion).
A 2007 fMRI study examining the difference in functional brain activation patterns associated with alien as compared to non-alien "volitional" movement in a patient with alien hand syndrome found that alien movement involved anomalous isolated activation of the primary motor cortex in the damaged hemisphere contralateral to the alien hand, while non-alien movement involved the normal process of activation described in the preceding paragraph in which primary motor cortex in the intact hemisphere activates in concert with frontal premotor cortex and posterior parietal cortex presumably involved in a normal cortical network generating premotor influences on the primary motor cortex along with immediate post-motor re-afferent activation of the posterior parietal cortex.
Combining these two fMRI studies, one could hypothesize that the alien behavior that is unaccompanied by a sense of agency emerges due to autonomous activity in the primary motor cortex acting independently of premotor cortex pre-activating influences that would normally be associated with the emergence of a sense of agency linked to the execution of the action.