Imagine your hand starting to move without you deciding to do so. She grabs objects, undoes what the other hand has just done, and seems to have a will of her own. This scenario worthy of a science fiction film is nevertheless very real: it is the “alien hand syndrome” or Alien hand syndrome, a neurological disorder as rare as it is fascinating.
Hand game, two hand game
This is what a 55-year-old man, a computer scientist, admitted to a neurology department in Abidjan, recently experienced. For several days, his left hand seemed to disobey him. She intervened without warning, contradicting the gestures of her right hand. When he opened a door, the left closed it. When he grabbed an object, she pushed him away.
“It’s a phenomenon that we learn very early in neurology, because it is fascinating from an anatomical point of view”explains Dr. Casseron, neurologist. “These patients often have damage to the corpus callosum, the large white matter structure that connects our two cerebral hemispheres. When this connection is broken, each hand can behave as if it belonged to a different person.”
The patient’s examinations actually revealed an infarction of the corpus callosum, responsible for this “diagonistic dyspraxia”. Literally, a conflict between the two hands.
When the brain loses control
Alien hand syndrome was first described in 1908, but it remains largely mysterious today. It manifests itself as involuntary, autonomous movements of a limb, usually the non-dominant hand, accompanied by a feeling of total loss of control.
“In a right-handed person, for example, the left hand can grab an object or obstruct the movement of the right hand without the person being able to stop it. continues Dr. Casseron. “It’s spectacular: you take something with your right hand, and your left hand stops you. Patients often talk about this with amazement or humor, some going so far as to give a name to their rebellious hand.”
The neurologist recalls that similar cases have also been observed in patients who have undergone a callosotomy, a voluntary section of the corpus callosum formerly performed to treat certain severe epilepsies.
A hand as “possessed”?
Funny indeed, in theory. For those affected, however, the sensation is destabilizing. Some say:“It’s not me, it’s my hand.” Dr Casseron confirms: “At first, many of these patients were thought to be crazy. Imagine: you unbutton your shirt with one hand, and the other immediately buttons it again! It’s crazy, literally.”
In so-called “frontal” forms, the hand seems incapable of resisting the urge to grasp everything it touches, a phenomenon already described by the French neurologist Jean Lhermitte (grandfather of Thierry Lhermitte) at the beginning of the 20th century. Other, more “pure” forms see the two hands entering into constant opposition.
“We must also clearly differentiate this syndrome from other disorders linked to body recognition”, specifies Dr Casseron. “For example, in certain lesions of the non-dominant hemisphere, we observe hemiasomatognosia: the patient no longer recognizes his paralyzed hand and considers it as that of another. But in the foreign hand, the hand really moves, without permission.”
The disorder has also inspired popular culture: in Doctor Strangelove (1964), the main character, played by Peter Sellers, cannot stop his hand from making the Nazi salute in spite of himself. A scene directly inspired by real clinical cases.
No miracle cure, but hope
To date, no cure exists, but rehabilitation and certain stimulations can help.
“As it is a disorder linked to an injury, we cannot “cure” it”, notes Dr. Casseron. “But we can sometimes improve control through stimulation or rehabilitation with an occupational therapist, particularly by working on the dominant hand to calm the rebellious hand.”
Treatment is also based on medications intended to reduce involuntary movements and psychological support to help patients accept this confusing phenomenon.
As Dr. Casseron summarizes, “this syndrome is proof that our brain is not a uniform block. It works in constant cooperation. And when this dialogue breaks down… our hands, sometimes, each start to speak their own language.”