I went to the NYU Consciousness site this morning hoping to see if the recent debate on the relationship of prefrontal activity to consciousness had been posted yet. It hasn’t, and based on what I can see, it might be a while.
But I did find this interesting debate from last year on whether split brain patients have two minds.
Just a reminder: split-brain patients were people who, in order to control severe epileptic seizures, had their corpus callosum, the connections between the two cerebral hemispheres of their brain separated. The procedure left them remarkably functional in day to day life, but careful tests show that the two sides of their brain have limited if any communication with each other, although recent experiments by one of the debaters complicates that understanding.
This debate includes David Chalmers as the MC, Elizabeth Schechter, who argues that split-brain patients do have two minds, Yair Pinto, who argues that they don’t, and Joseph Ledoux, who argues that the issue is complicated and depends on the specific patients and which definitions we’re using.
Just so you know what you’re getting into, the video is two hours long, although the initial statements from the participants are done within the first hour.
I’m not sure if I’d heard of Schechter before. I found her views interesting and might have to explore them at some point. Unfortunately, her book appears to be pricey. I noted above that she argues for two minds, but her view turns out be nuanced and not really too different from Ledoux’s. She sees there being two minds, but one person.
My own conclusions on this is that I don’t think it’s productive to talk about there being two separate minds. All of the tests do show that communication between the hemispheres are limited to some degree or another, but I think it’s more accurate to talk about fragments of a mind whose communications are disrupted.
Pinto makes much about the fact that the two hemispheres don’t seem to notice or be bothered by the separation. But I think that is only an issue if we regard each hemisphere as its own separate self. However, the hemispheres didn’t evolve that way. They evolved to be a portion of a self, and it’s clear that’s what they expect to be.
V.S. Ramachandran in his book, The Tell-Tale Brain, relates the power of the brain’s expectations of its body plan. When that expectation, due to some brain injury, becomes disrupted, in a condition known as apotemnophila, it can lead to conditions where people no longer feel a limb is theirs, with an intensity that can lead them seek to have it amputated.
If each hemisphere has a plan for its side of the body, then it wouldn’t expect to receive signals from the other side, much less be able to control it. Indeed, if it suddenly found that it could, it might result in the apotemnophila condition.
So we end up with fragments of a mind whose communications have become limited. Over time, split-brains either recruit remaining subcortical pathways, or learn to use subtle external behavioral cues to make up for the limitation. This seems to bridge the results from the old Sperry / Gazzaniga / Ledoux results and the newer ones from Pinto.
It’s also a stark reminder of just how married mental processes are to their embodiment.