So, what is your corpus callosum? It is the white matter bridge between the two halves of your brain. If you have damaged it, one side of the brain cannot tell the other side what is going on. Here is a way to test whether your corpuse callosum is working.

http://www.mindhacks.com/blog/2008/0...orpus_cal.html
I've just discovered a wonderfully simple finger touch procedure that can test the function of your corpus callosum, a key brain structure that connects the two cortical hemispheres.

It is called the 'cross lateralization of fingertips test' and was used in a 1991 study by Kazuo Satomi and colleagues.

It relies on the fact that different hemispheres are responsible for the movements and sensations from each hand.

In other words, each hand is connected to a different side of the brain, and, to allow you to co-ordinate both hands, the brain passes information between the two sides by using the corpus callosum.

The corpus callosum is the largest structure in the brain and works like a huge bundle of white matter 'cables', connecting different areas.

If this structure gets damaged, a patient might have trouble with coordinating their hands, preventing them from matching sensations on one hand with movement on the other, because the information doesn't get to where it's needed.

The test works like this: you need to ask someone to close their eyes and put their hands face up.

You then touch one of their fingertips with a pencil, and with the opposite hand the participant needs to touch the corresponding finger with thumb of the same hand.

For example, if you touched their right ring finger, they would need to touch their left ring finger with their left thumb, as shown in the diagram above.

You need to do this on both hands, with them always touching the corresponding finger on the opposite hand.

It's important that the person keeps their eyes closed, because as soon as they look, they get information from the eyes, which goes to both hemispheres.

Patients who have damage to the corpus callosum (either because of acquired damage or because it just hasn't developed) usually can't do this test, because of the disruption in communication between the two hemispheres of the brain.