Corpus callosum Damage to the corpus callosum can give rise to "purposeful" actions in the sufferer's non-dominant hand (an individual who is left-hemisphere-dominant will experience the left hand becoming<unk> , and the right hand will turn<unk>  in the person with right-hemisphere dominance). In "the callosal variant", the patient's hand counteracts voluntary actions performed by the other, "good" hand. Two phenomena that are often found in patients with callosal<unk>  hand are agonistic dyspraxia and diagonistic dyspraxia. Agonistic dyspraxia involves compulsive automatic execution of motor commands by one hand when the patient is asked to perform movements with the other hand. For example, when a patient with callosal damage was instructed to pull a chair forward, the affected hand would decisively and impulsively push the chair backwards. Agonistic dyspraxia can thus be viewed as an involuntary competitive interaction between the two hands directed toward completion of a desired act in which the affected hand competes with the unaffected hand to complete a purposive act originally intended to be performed by the unaffected hand. Diagonistic dyspraxia, on the other hand, involves a conflict between the desired act in which the unaffected hand has been engaged and the interfering action of the affected hand which works to oppose the purpose of the desired act intended to be performed by the unaffected hand. For instance, when Akelaitis's patients underwent surgery to the corpus callosum to reduce epileptic seizures, one patient's left<unk>  hand would frequently interfere with the right hand. For instance, while trying to turn over to the next page with the right hand, his left hand would try to close the book. In another case of callosal<unk>  hand, the patient did not suffer from intermanual conflict between the hands but rather from a symptom characterized by involuntary mirror movements of the affected hand. When the patient was asked to perform movements with one hand, the other hand would involuntarily perform a mirror image movement which continued even when the involuntary movement was brought to the attention of the patient, and the patient was asked to restrain the mirrored movement. The patient suffered from a ruptured aneurysm near the anterior cerebral artery, which resulted in the right hand being mirrored by the left hand. The patient described the left hand as frequently interfering and taking over anything the patient tried to do with the right hand. For instance, when trying to grasp a glass of water with the right hand with a right side approach, the left hand would involuntary reach out and grasp hold of the glass through a left side approach. More recently, Geschwind et al. described the case of a woman who suffered severe coronary heart disease. One week after undergoing coronary artery bypass grafting, she noticed that her left hand started to "live a life of its own". It would unbutton her gown, try to choke her while asleep and would automatically fight with the right hand to answer the phone. She had to physically restrain the affected hand with the right hand to prevent injury, a behavior which has been termed "self-restriction". The left hand also showed signs of severe ideomotor apraxia. It was able to mimic actions but only with the help of mirror movements executed by the right hand (enabling synkinesis). Using magnetic resonance imaging (MRI), Geschwind et al. found damage to the posterior half of the callosal body, sparing the anterior half and the splenium extending slightly into the white matter underlying the right cingulate cortex. Park et al. also described two cases of infarction as the origin of<unk>  hand symptoms. Both individuals had suffered an infarction of the anterior cerebral artery (ACA). One individual, a 72-year-old male, had difficulty controlling his hands, as they often moved involuntarily, despite his trying to stabilize them. Furthermore, he often could not let go of objects after grasping them with his palms. The other individual, a 47-year-old female who suffered 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. Her left hand could also sense when her right hand was holding an object and would involuntarily, forcibly take the object out of her right hand. Frontal lobe Unilateral injury to the medial aspect of the brain's frontal lobe can trigger reaching, grasping and other purposeful movements in the contralateral hand. With anteromedial frontal lobe injuries, these movements are often exploratory reaching movements in which external objects are frequently grasped and utilized functionally, without the simultaneous perception on the part of the patient that they are "in control" of these movements. Once an object has been acquired and is maintained in the grasp of this "frontal variant" form of<unk>  hand, the patient often has difficulty with voluntarily releasing the object from grasp and can sometimes be seen to be peeling the fingers of the hand back off the grasped object using the opposite controlled hand to enable the release of the grasped object (also referred to as tonic grasping or the "instinctive grasp reaction"). Some (for example, the neurologist Derek Denny-Brown) have referred to this behavior as "magnetic apraxia" Goldberg and Bloom described a woman who suffered a large cerebral infarction of the medial surface of the left frontal lobe in the territory of the left anterior cerebral artery which left her with the frontal variant of the<unk>  hand involving the right hand. There were no signs of callosal disconnection nor was there evidence of any callosal damage. The patient displayed frequent grasp reflexes; her right hand would reach out and grab objects without releasing them. In regards to tonic grasping, the more the patient tried to let go of the object, the more the grip of the object tightened. With focused effort the patient was able to let go of the object, but if distracted, the behaviour would re-commence. The patient could also forcibly release the grasped object by peeling her fingers away from contact with the object using the intact left hand. Additionally, the hand would scratch at the patient's leg to the extent that an orthotic device was required to prevent injury. Another patient reported not only tonic grasping towards objects nearby, but the<unk>  hand would take hold of the patient's penis and engage in public masturbation. Parietal and occipital lobes A distinct "posterior variant" form of<unk>  is associated with damage to the posterolateral parietal lobe and/or occipital lobe of the brain. The movements in this situation tend to be more likely to withdraw the palmar surface of the hand away from sustained environmental contact rather than reaching out to grasp onto objects to produce palmar tactile stimulation, as is most often seen in the frontal form of the condition. In the frontal variant, tactile contact on the ventral surface of the palm and fingers facilitates finger flexion and grasp of the object through a positive feedback loop (i.e. the stimulus generates movement that reinforces, strengthens and sustains the triggering stimulation). In contrast, in the posterior variant, tactile contact on the ventral surface of the palm and fingers is actively avoided through facilitation of extension of the fingers and withdrawal of the palm in a negative feedback loop (i.e. the stimulus, and even anticipation of stimulation of the palmar surface of the hand, generates movement of the palm and fingers that reduces and effectively counteracts and eliminates the triggering stimulation, or, in the case of anticipated palmar contact, decreases the likelihood of such contact).<unk>  movements in the posterior variant of the syndrome also tend to be less coordinated and show a coarse ataxic motion during active movement that is generally not observed in the frontal form of the condition. This is generally thought to be due to an optic form of ataxia since it is facilitated by the visual presence of an object with visual attention directed toward the object. The apparent instability could be due to an unstable interaction between the tactile avoidance tendency biasing toward withdrawal from the object, and the visually based acquisition bias tendency pushing toward an approach to the object. The<unk>  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.<unk>  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. The<unk> " movements, however, remain purposeful and goal-directed, a point which clearly differentiates these movements from other disorganized non-purposeful
Alien hand syndrome
Hunan hand syndrome
Split hand syndrome
Elejalde syndrome
Achard syndrome
Scimitar syndrome
Reynolds syndrome
Duane-radial ray syndrome