Recently I posted some videos of Roger Sperry’s research into lateralisation of function in epileptic patients who had had their corpus callosum severed to varying degrees. Now for more Sperry related goodies: how to test your corpus callosum (and no surgery is needed!). Basically all you have to do is:
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.
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. [thanks to Mind Hacks]
The test is called the cross lateralization of fingertips test and is something we can all try. This simple yet effective test was developed by Satomi et al:
If defective cross-localization of fingertips (CLF) in callosal patients is due to a deficit in the interhemispheric transfer of somesthetic information, when the patient’s eyes are open, CLF should be affected when the stimulated hand is excluded from vision, not when the responding hand is excluded from vision. [link to abstract]
Basically, in proper English, people who either don’t have or have an underdeveloped corpus callosum will have difficulties with this test as you’re asking them to pass sensory information from one hemisphere (the hemisphere that corresponds to the hand that was touched) and the other hemisphere (the one that has to move to demonstrate which finger was touched).
Hat tip to Mind Hacks.