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When You Split the Brain, Do You Split the Person? (aeon.co)
An anonymous reader shares an article: The brain is perhaps the most complex machine in the Universe. It consists of two cerebral hemispheres, each with many different modules. Fortunately, all these separate parts are not autonomous agents. They are highly interconnected, all working in harmony to create one unique being: you. But what would happen if we destroyed this harmony? What if some modules start operating independently from the rest? Interestingly, this is not just a thought experiment; for some people, it is reality. In so-called 'split-brain' patients, the corpus callosum -- the highway for communication between the left and the right cerebral hemispheres -- is surgically severed to halt otherwise intractable epilepsy. [...] What, then, happens to the person? If the parts are no longer synchronised, does the brain still produce one person? The neuroscientists Roger Sperry and Michael Gazzaniga set out to investigate this issue in the 1960s and '70s, and found astonishing data suggesting that when you split the brain, you split the person as well. Sperry won the Nobel prize in medicine for his split-brain work in 1981. [...] Case closed? Not to me. [...] To try to get to the bottom of things, my team at the University of Amsterdam re-visited this fundamental issue by testing two split-brain patients, evaluating whether they could respond accurately to objects in the left visual field (perceived by the right brain) while also responding verbally or with the right hand (controlled by the left brain). Astonishingly, in these two patients, we found something completely different than Sperry and Gazzaniga before us. Both patients showed full awareness of presence and location of stimuli throughout the entire visual field -- right and left, both.
Earlier experiments used a partition to separate the left and right visual fields. One experiment I recall reading about was done like this: On one side of the partition they would place an implement, such as a fork. They would then have the subject pick up the implement in one hand and ask them to identify it, and do various things with it. The results were markedly different depending on which side of the partition, and therefore which eye and which hand, were engaged.
Here is some general information on the early experiments.
I've fallen off your lawn, and I can't get up.
This isn't a thought experiment though. We have actual split-brain patients and we can see how they react. I'm not sure why you think that this kills the patient either, since for most purposes, such patients act very similarly to how they did before the procedure.
CGP Grey did a nice, insightful piece on this in a 5 minute youtube piece discussing just this thing. I like his videos in general ...
The corpus callosum isn't the only connection between the left and right half of the brain.
The architecture of the human brain is a bit like an onion; at the core is the basal ganlia -- also popularly known as the "reptilian brain". Outside/above that is the limbic system, called the "paleomammalian complex" in the triune brain theory. Above that is the neocortex, the part we tend to indentify ourselves with because it does all the cool stuff that more primitive organisms can't, like language.
The corpus callosum sits roughly in the middle of the limbic system -- the middle of the middle if you will. Just above it is the cingulate gyrus, responsible for processing emotions, learning, linking behavior to goals. The cingulate gyrus is the anatomicaly lowest part of the brain that doesn't have its own connections between hemispheres. I find that fascinating and suggestive. Immediately below the corpus callosum is the septum pellucidum, which is a thin, midline structure. Every part of the brain below the septum pellucidum is richly connected across sides.
This situation is like a company run by partners. The partners don't talk to each other, but they share subordinates, including a secretary who keeps them up to date on what each other is doing. The secretary quits, and the company is at least temporarily less coordinated, but the other subordinates still talk to each other and over time may take up some of the communication burden.
One of the big difference in brain science today from when I studied it thirty years ago is that we know the brain is much more plastic than we ever imagined. There have been well-documented cases of people with brain injuries doing things they taught me was impossible back then, like people who lost an entire brain hemisphere regaining some motor control on the affected side. The only way this would be physically possible is for the remaining hemisphere to radically remodel itself.
Anyhow cross visual field object awareness is a good candidate for function restoration, because the nerves from the eyes enter the brain well below the level of the corpus callosum; there are no direct connections from the optic nerves to the cortex. How that awareness comes about/is restored is an open question. It could be that the cortexes develop other way of communicating, or it could be that the hemisphere you're talking to develops awareness of stuff that would normally be processed by the other side.
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