How does Alien Hand Syndrome work?

In order to understand what we know about alien hand syndrome, we should take a brief look at the brain and how it works. The human brain is divided into two hemispheres, each consisting of four different lobes, all working together to create, control and regulate speech, movement, emotion and about a billion other sub-functions. The frontal lobe is the section responsible for motor skills, like movement and speech, and cognitive functions, like planning and organization, and it's a good place to start in our understanding of AHS.

Let's concentrate on the planning and organization. Let's say you want to take a sip of your morning coffee. What seems like a simple task is really a complex sequence of brain functions, starting from the moment you think, "Mmmm, coffee."

When you make the decision to sip the coffee, a signal originates in the frontal lobe that plans and organizes what must take place in order for that action to be completed. You need to reach for the cup, grasp the handle, bring it to your lips, sip ans swallow, then return the cup and release your grasp.

Theses signals are then sent to the motor strip, the area that runs from the top of your head down to the ear, and is responsible for controlling all of your body's movement.

The frontal lobe tells the motor strip, "Hey, I need some coffee, do your thing," and before you know it, you're enjoying your nice morning roast. The key in making this happens is the successful sending of messages, thanks to the corpus callosum.


Think of the corpus callosum as the brain's e-mail server, a bundle of message sending nerves that connect and share information with the two hemispheres. Alien hand syndrome is a result of damage to these nerves. This damage most often occurs in brain aneurysms, stroke patients and those with infections of the brain, but can also manifest as a side effect of brain surgery, most commonly after a radical procedure that treats extreme cases of epilepsy. When the callosum is damaged, it leaves the different sections of the brain disconnected and unable to speak to each other - its e-mail is permanently down. With AHS, one hand functions normally, carrying out purposeful tasks without signaling the other hand, resulting in a limb that can act on its own, sometimes in opposition to the functioning side.

New research about Alien Hand Syndrome

Research has been sparse over the years due to the scarcity of cases, but a study by team of Swiss doctors in July 2007 has shed new light on AHS. The doctors conducted functioning magnetic resonance imaging (fMRI) tests on a victim of AHS to determine what sections of the brain showed activity during planned and unplanned movements. They found that planned movements originated in the frontal lobe before being sent to the motor strip, while the alien movements showed no activity in the frontal lobe - the movements originated from the motor strip itself. Furthermore, the signal remained in the motor strip without sending a message back to the frontal lobe, leaving victims unaware of their own movements. While the motor strip has finally been successfully singled out as the center of activity, it's still not known what triggers the signals to begin with, leaving the condition as a mysterious medical curiosity.

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