Split Brain Might Not Lead to Two Consciousnesses After All

“The human mind can be divided with a knife,” Harris says. A person will remain conscious with either half of their brain removed completely, but if the halves are merely separated they can hold different opinions and argue with each other (which we experience to some degree under normal conditions.)

Harris offers a few “things that make you go hmmmmm.” What if one hemisphere accepts Jesus Christ as Lord and Savior and the other says all organized religion is nonsense? Is one half of the brain “saved” while the other is doomed? Or should we view such a person as we would view the soul of a dying infant – saved because they are incapable of making a decision? If such a person was half Democrat and half Republican, how could they vote? Do they have to abstain, or do they deserve two votes for two seats of consciousness in one body? And are we really any different now, with a thin connection in the brain that allows some communication between hemispheres? As Harris says, “How can our brains not harbor multiple centers of consciousness even now?”

But new research suggests that the division within the brain(s?) is nowhere near as severe as earlier research suggests.

Split brain does not lead to split consciousness – University of Amsterdam

I’ve talked before about Roger Perry’s famous split-brain patient experiments. Patients with severe epileptic seizures used to undergo a collosotomy, a procedure to cut the connections between the left and right hemispheres of their cerebrum. It often helped alleviate their symptoms and, remarkably, the patients afterward remained mentally functional, at least to outside appearances.

Each hemisphere of the brain controls and receives sensory input from half the body. What Perry and his colleagues discovered in their experiments, was that if sensory inputs going into the patient were isolated to one hemisphere or the other, each of the patient’s hemispheres were only aware of its own sensations, and with the language centers usually focused on the left hemisphere, the patient could usually only describe what they were seeing when the left hemisphere received it.

The fact that the patients, post-procedure, remained largely functional seemed to show that each hemisphere was effectively watching what the other half of the body did, and mentally confabulating the actions as its own. It opened up the possibility that this happens even in healthy people, albeit to a lesser extent.

However, new research appears to show that this phenomenon may be more limited than previously thought:

A new research study contradicts the established view that so-called split-brain patients have a split consciousness. Instead, the researchers behind the study, led by UvA psychologist Yair Pinto, have found strong evidence showing that despite being characterised by little to no communication between the right and left brain hemispheres, split brain does not cause two independent conscious perceivers in one brain. Their results are published in the latest edition of the journal Brain.