The old idiom to “not let the left hand know what the right hand is doing”, has taken on new, literal meaning with Alien Hand Syndrome (AHS). In this extremely rare neurological condition, with only about 50 documented cases in the past 111 years, a person loses mental control of their subordinate limb — most often, the hand — and, to their horror, finds that the limb makes involuntary actions that seem to be controlled by another force entirely. This can result in bizarre behavior that not only does the person have no control over, they also generally have no awareness of until they catch the alien limb in the act.

Documented behaviors include:

  • Compulsive grasping and fidgeting
  • Stroking the face and hair
  • Levitating limb
  • Undressing/unbuttoning clothes
  • Stuffing food in the mouth
  • Grabbing an object without letting go, requiring the other hand to pry the object out of its grasp
  • In extreme cases, strangling the neck or punching the face.

A person afflicted with Alien Hand Syndrome may be able to feel sensation in their alien limb, but they will not have control over the limb itself. There is a sense of disassociation, as if the person’s limb is not their own, and in many cases they refer to it in the third person, such as “the hand” or even, “the monster”.  It may also feel as if they have an extra limb.

In addition to not recognizing the alien limb as one’s own, and feeling as if they are being controlled or attacked by someone else, there are also associated feelings of fright, terror, and anxiety. One woman with AHS needed a Valium injection during a clinical session, after seeing her left arm coming at her and begging: “Look, it’s coming… please help me.”

Sometimes episodes are isolated, but for the most part, the alien limb is active at all times (when the body isn’t sleeping), and the condition can last from several days to several years. Weakness and numbness may occur on the side of the same side of the body as the alien limb.

AHS was first documented in Germany by Dr. Kurt Goldstein in 1908, when his patient, aged 57, reported that her left hand had a “will of its own”, and on occasion would begin to strangle her throat, requiring her to use her other hand to remove it.

Since then, there have only been approximately fifty documented cases. In 1972, the condition was officially labeled Alien Hand Syndrome (AHS), and perhaps not surprisingly due to its sensational aspects, it was also picked up by Hollywood. Alien Hand Syndrome has been portrayed in pop culture to horrific or comedic effect, most famously in Stanley Kubrick’s 1964 film “Dr. Strangelove”. In it, the title character played by Peter Sellers is routinely battling with his right arm, which involuntarily gives the Nazi Party salute, as seen in the clip below:

Alien Hand Syndrome has also appeared in the movie “Liar, Liar” and the TV shows “Angel” and “The Simpsons”.

What causes Alien Hand Syndrome? It is a neurological condition, and in most cases it is a result of brain damage. Rarely, it is due to head injury, stroke, aneurysm, tumor, or Alzheimer’s disease. Damage to the parietal lobe or occipital lobe results in the slightest cases, with the hand avoiding contact with objects in its environment by levitating or floating above them with its fingers extended.

The more extreme cases involve damage to the corpus callosum, which is the connector between the two hemispheres of the brain. During brain surgery (corpus callosotomy) for extreme cases of epilepsy, the nerve fibers that link the two sides of the brain are severed. This damage is present in most severe cases of AHS, in which the limb seems to have its own will and the person is unaware of what the limb is doing.

One of the most bizarre presentations of Alien Hand Syndrome is due not to surgery but to lesions on the corpus callosum, resulting in what is called intermanual conflict – the alien hand being always at odds with what the self-controlled hand is doing. For example, putting on a shirt, picking up a remote to watch TV, or lighting a cigarette all become impossible tasks, as whatever the self-controlled hand does, the alien hand immediately undoes. These conflicts are generally minor, however there have been instances when it’s turned dangerous, such as the alien hand trying to strangle or punch the person, or take control of the steering wheel and turn erratically while driving. One patient whose AHS was the result of a stroke was severely embarrassed when his alien hand began engaging in public masturbation.

Scientists still don’t know exactly why AHS presents the way it does, but it’s thought that the damage to the corpus callosum leaves the dominant hemisphere with the ability to control the dominant hand only. The subordinate hand then seems to be driven only by the brain’s motor strip (the area that runs from the top of the head down to the ear) – and in cases of AHS, what’s signaling the motor strip is still unknown. A study by a team of Swiss researchers in 2007 using fMRI tests showed that the movements seemed to originate within the motor strip itself. The signal also did not reach the frontal lobe, which is why patients were unaware of the movements.

There is no known treatment or cure, and at best patients seem to be able to manage it by giving the alien hand an object to hold.