Study: Split brain fails to yield split consciousness

"I was so surprised that I decide repeat the experiments several more times with all types of control," said researcher Yair Pinto.

By Brooks Hays

Jan. 25 (UPI) -- New experiments show split brains don't produce split consciousness, as previously theorized.

A split brain is not one sawed in two, but a brain with a severed corpus callosum, the bundle of neural fibers connecting the brain's left and right hemispheres. In the 1940s, doctors began splitting the corpus callosum of patients with severe epilepsy as a way to prevent epileptic symptoms from spreading.


The procedure, a corpus callosotomy, was successful at relieving epileptic symptoms, but not surprisingly, it came with side effects. Researchers soon discovered split-brain patients could respond with their right hand to stimuli in their right visual field, and with their left hand to stimuli in their left visual field.

Scientists theorized the hemispheres of a split brain develop their own consciousness.

Researchers at the University of Amsterdam decided to test the theory. They presented two participants, with fully severed corpus callosums, a series of images on a computer screen. The participants were asked to confirm the presence of an object and identify its location. A follow-up test asked the participants to name the object they had just witnessed.

"Our main aim was to determine whether the patients performed better when responding to the left visual field with their left hand instead of their right hand and vice versa," University of Amsterdam psychologist Yair Pinto said in a news release. "This question was based on the textbook notion of two independent conscious agents: one experiencing the left visual field and controlling the left hand, and one experiencing the right visual field and controlling the right hand."


Surprisingly, participants successfully identified the presence of stimuli in all locations using all three responses -- left hand, right hand and verbal.

"The patients could accurately indicate whether an object was present in the left visual field and pinpoint its location, even when they responded with the right hand or verbally," Pinto explained. "This despite the fact that their cerebral hemispheres can hardly communicate with each other and do so at perhaps 1 bit per second, which is less than a normal conversation. I was so surprised that I decide repeat the experiments several more times with all types of control."

The findings, published in the journal Brain, suggest unified consciousness doesn't require a large amount of communication between the two hemispheres.

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