At times, particularly in individuals who have sustained damage to the corpus callosum that connects the two cerebral hemispheres (see also Split-brain), the hands appear to be acting in opposition to each other.
[11] 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.
[12][13] 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.
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 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".
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.
[21] 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.
[citation needed] As noted above, these ideas can also be linked to the concept of efference copy and re-afference, where efference copy is a signal postulated to be directed from premotor cortex (activated normally in the process associated with emergence of an internally generated movement) over to somatosensory cortex of the parietal region, in advance of the arrival of the "re-afferent" input generated from the moving limb, that is, the afferent return from the moving limb associated with the self-generated movement produced.
[citation needed] One theory posed to explain these phenomena proposes that the brain has separable neural "premotor" or "agency" systems for managing the process of transforming intentions into overt action.
[25] Damage to this anteromedial premotor system produces disinhibition and release of such exploratory and object acquisition actions which then occur autonomously.
These two intrahemispheric systems, each of which activates an opposing cortical "tropism", interact through mutual inhibition that maintains a dynamic balance between approaching toward (in other words, with "intent-to-capture" in which contact with and grasping onto the attended object is sought) versus withdrawing from (that is, with "intent-to-escape" in which distancing from the attended object is sought) environmental stimuli in the behavior of the contralateral limbs.
[citation needed] When the anteromedial frontal "escape" system is damaged, involuntary but purposive movements of an exploratory reach-and-grasp nature – what Denny-Brown referred to as a positive cortical tropism – are released in the contralateral limb.
[26][27] This is referred to as a positive cortical tropism because eliciting sensory stimuli, such as would result from tactile contact on the volar aspect of the fingers and palm of the hand, are linked to the activation of movement that increases or enhances the eliciting stimulation through a positive feedback connection (see discussion above in section entitled "Parietal and Occipital Lobes").
[citation needed] When the posterolateral parieto-occipital "approach" system is damaged, involuntary purposive movements of a release-and-retract nature, such as levitation and instinctive avoidance – what Denny-Brown referred to as a negative cortical tropism – are released in the contralateral limb.
[27] This is referred to as a negative cortical tropism because eliciting sensory stimuli, such as would result from tactile contact on the volar aspect of the fingers and palm of the hand, are linked to the activation of movement that reduces or eliminates the eliciting stimulation through a negative feedback connection (see discussion above in section entitled "Parietal and Occipital Lobes").
[citation needed] Each intrahemispheric agency system has the potential capability of acting autonomously in its control over the contralateral limb although unitary integrative control of the two hands is maintained through interhemispheric communication between these systems via the projections traversing the corpus callosum at the cortical level and other interhemispheric commissures linking the two hemispheres at the subcortical level.
[31] One week after undergoing coronary artery bypass grafting, she noticed that her left hand started to "live a life of its own".
The other individual, a 47-year-old female with an ACA in a different location of the artery, complained that her left hand would move on its own and she could not control its movements.
[32] Unilateral injury to the medial aspect of the brain's frontal lobe can trigger reaching, grasping and other purposeful movements in the contralateral hand.
[citation needed] The alien limb in the posterior variant of the syndrome may be seen to "levitate" upward into the air withdrawing away from contact surfaces through the activation of anti-gravity musculature.
Alien hand movement in the posterior variant may show a typical posture, sometimes referred to as a "parietal hand" or the "instinctive avoidance reaction" (a term introduced by neurologist Derek Denny-Brown as an inverse form of the "magnetic apraxia" seen in the frontal variant, as noted above), in which the digits move into a highly extended position with active extension of the interphalangeal joints of the digits and hyper-extension of the metacarpophalangeal joints, and the palmar surface of the hand is actively pulled back away from approaching objects or up and away from supporting surfaces.
[citation needed] In both the frontal and the posterior variants of the alien hand syndrome, the patient's reactions to the limb's apparent capability to perform goal-directed actions independent of conscious volition is similar.
[30] However, the symptoms can be reduced and managed to some degree by keeping the alien hand occupied and involved in a task, for example by giving it an object to hold in its grasp.
Other techniques proven to be effective include; wedging the hand between the legs or slapping it; warm water application and visual or tactile contact.
[37] Additionally, Wu et al.[38] found that an irritating alarm activated by biofeedback reduced the time the alien hand held an object.
Exactly how this may occur is not well understood, but a process of gradual recovery from alien hand syndrome when the damage is confined to a single cerebral hemisphere has been reported.
Other individuals have reported using an orthotic device to restrict perseverative grasping[22] or restraining the alien hand by securing it to the bed pole.
[citation needed] Theoretically, this approach could slow down the process through which voluntary control of the hand is restored if the neuroplasticity that underlies recovery involves the recurrent exercise of voluntary will to control the actions of the hand in a functional context and the associated experiential reinforcement through successful willful suppression of the alien behavior.
With significant effort, she was able to move her left arm in response to spoken command, but conscious movements were slower or less precise than similar involuntary motions.
[41] In his classic papers reviewing the wide variety of disconnection syndromes associated with focal brain pathology, Norman Geschwind commented that Kurt Goldstein "was perhaps the first to stress the non-unity of the personality in individuals with callosal section, and its possible psychiatric effects".