Triviality VIII: Alien Hand Syndrome

OK, Triviality time! (I apologise for the hiatus but I promise to readers that by the time school starts in September I will be at least past 20.) Edit 8/29/13: I got up to 18. Not bad.

Today's subject is Alien Hand Syndrome (AHS), also known as Dr. Strangelove syndrome, or anarchic hand syndrome (freaky) presumably from that one movie back in the '60s.

It's rather fascinating (to me, that is - not to people who suffer from it). It's a very rare neurological problem, commonly in the corpus callosum (which is the gap that connects the two halves of the brain together). It involves a hand having "a life of its own" and doing its own thing.

It's all in the hand.

People with AHS have full sensation of the hand, meaning that they can feel the hand being there, it isn't numb, pain is felt, etc. However, that person cannot control the hand and its motions (I should note that it is intermittent most of the time: the hand isn't always like that.)

I've read some accounts of AHS, and apparently patients can be doing anything and their hand will suddenly try to strangle them, pick up things and throw them, and much more. Extremely disturbing and very freaky. Imagine typing and then your hand typing whatever it wanted, controlling the mouse, etc.

Please note that tremors, shakes, and other unconscious physiological conditions that happen involuntarily (in English: spasms and other normal quirks our muscles have) do not count.

Do not get this injured under pain of AHS

AHS was first diagnosed/recorded in 1908, and since then there have been a steady but rare amount of people with the disorder. Oftentimes the disorder comes about after brain surgery, if the corpus calosum has been cut or severed, since that counts as injury.

So, how does injury to the corpus callosum cause this?

In brief: the corpus callosum connects your motor nerve (the part of the brain that controls your movements) and your frontal lobe (which controls your thoughts and actions). Injury to the corpus callosum will damage these nerves, which means thoughts with no action, or vice versa, which happens here: actions with no thought behind it. Hence, the "mind of its own" light that pervades AHS.

This is basically a very, very, very, very rough way to explain AHS - the brain is a very complex mechanism (note: NOT a computer - computers can be controlled) and AHS is really very little known. As stated above it was discovered in 1908 but not fully defined until the 70's. Even now we still have a very rough estimate of how AHS works. The mind's a tricky thing.

There are 3 different types of AHS which I will briefly outline:

I: The hand reaches for things that are just out of its reach or have recently been removed from its grasp
II: (I dub this the troll hand) The hand counteracts things the good hand did. If your good hand opens a door, the anarchic hand will close it. If you put on a hat, your alien hand will remove it.
III: (rarest type) Anesthetic effects, the hand often does not feel part of the body and the person does not recognize the hand.

Alien Hand Syndrome has been shown in many medical shows, not least House. (Season 5 finale, if you must know). TV Tropes dubs this the "Evil Hand".

Believe me, from the sound of this, this is one disorder you DON'T want. Even if it sounds cool, believe me, it doesn't.

-Rob


And here - because I feel I should actually give evidence for my research:
Resources: HowStuffWorks, DamnInteresting, Polite Dissent, James S. McDonnell Foundation, and TVTropes.