This film clip shows Michael Gazzaniga carrying out a behavioural study of a split brain patient named Joe.
The split brain procedure (or corpus callosumectomy) involves severing of the corpus callosum, the bundle of approximately 100 million nerve fibres that connect the two hemispheres of the brain.
The procedure was performed on patients with intractable epilepsy, the idea being that preventing the left and right hemispheres from communicating with each other would stop the abnormal electrical activity associated with epilepsy from spreading across the whole brain.
Split brain patients can lead normal lives but, as this film clip shows, they exhibit bizarre behaviours under experimental conditions as a result of their surgery.
Normally, the left hemisphere of the brain controls, and receives sensory inputs from, the right side of the body, and vice versa (this is known as contralateral control). Thus, visual information entering the left side of the left eye is sent to the right visual cortex, and information from the right side of the right retina is sent to the left visual cortex.
As demonstrated by Joe, information presented to his right visual field does not cross to the left hemisphere. Consequently, Joe cannot say the words presented to his right visual field.
This is because the speech centres are found in the left hemisphere (at least, this is the case for most right-handed people), and the visual information presented on the left side of the screen cannot cross to those parts of the brain involved in speech production. Joe can, however, use his right hand to draw a simple diagram of the object he is unable to name.
(Via Mind Hacks)
Comments (3)
That must be a very surreal feeling for Joe - seeing one shape but drawing another with his left hand. I can't even imagine what it would feel like. Almost like someone was guiding his hand while drawing, as he has no recollection of ever seeing the left image. Crazy :)
Posted by: Zachary Tong | September 17, 2007 12:15 PM