Matt Rouge recently reminded me of a study that came out in 2017, purporting to show that split-brain patients retain a single locus of consciousness. Although I put up a brief post about it at the time, I don't think I fully appreciated the implications.
In a corpus callosotomy, the sheaf of neural fibers connecting the left and right cerebral hemispheres is surgically severed. A connection between the< hemispheres remains intact, but is considered too weak to provide more than minimal communication. Decades ago, split-brain patients were tested in a famous series of experiments, as Science Daily explains:
In their canonical work, [Roger] Sperry and [Michael] Gazzaniga discovered that split-brain patients can only respond to stimuli in the right visual field with their right hand and vice versa. This was taken as evidence that severing the corpus callosum causes each hemisphere to gain its own consciousness.
This conclusion, in turn, has been used by skeptics to argue that consciousness is generated by the brain and therefore cannot survive death. I don't necessarily think this argument has the force it's supposed to have. One could argue that if the brain serves as a filter for extracerebral consciousness, then if it is cut in half, it simply functions as two filters. By way of analogy, a funnel that produces a sound by channeling a wind current would produce two sounds if it were somehow made into two funnels. There would still be only one current of wind.
In any case, a more recent study casts doubt on Sperry and Gazzaniga's conclusions:
[Yair] Pinto and his fellow researchers conducted a series of tests on two patients who had undergone a full callosotomy.... To the researchers’ surprise, the patients were able to respond to stimuli throughout the entire visual field with all the response types: left hand, right hand and verbally. Pinto: ‘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. 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.’
According to Pinto, the results present clear evidence for unity of consciousness in split-brain patients. ‘The established view of split-brain patients implies that physical connections transmitting massive amounts of information are indispensable for unified consciousness, i.e. one conscious agent in one brain. Our findings, however, reveal that although the two hemispheres are completely insulated from each other, the brain as a whole is still able to produce only one conscious agent. This directly contradicts current orthodoxy and highlights the complexity of unified consciousness.’
It would appear that at least one set of researchers has made a mistake somewhere, since their results directly contradict each other. If the more recent experiments hold up to scrutiny, the implications are pretty serious.
In my post from 2017, I focused on the possibility that a common argument against survival had been undermined. But when I look at it now, it occurs to me that Pinto's study amounts to something close to positive evidence for survival. After all, if the two hemispheres of the brain still have a single locus of consciousness despite minimal connectivity, it would strongly suggest that consciousness originates outside the brain and simply uses the brain as an instrument — or at the very least, that consciousness, having originated in the brain, assumes some kind of extracerebral status that can persist even when the brain has been seriously impaired.
In other words, either consciousness originates in "the cloud" and is downloaded to the brain as needed, or consciousness originates in the brain and is periodically uploaded to "the cloud" for safekeeping. Either way, the destruction of the brain at death should not necessarily affect the content stored in the cloud.
For what it's worth, my personal view is that both of these options are correct: there is a give-and-take relationship between the brain and consciousness, similar to the back-and-forth communications between a Mars Rover and Mission Control, with data from the Rover transmitted to Mission Control, and Mission Control analyzing those data and sending back instructions. Note that the Rover has a degree of autonomy, analogous to reflex, instinct, or any learned behavior that has become automatic; it can respond immediately to certain problems without waiting for advice from Mission Control. I believe I first came across the Rover analogy in The Biology of Belief by Bruce Lipton.
Additional evidence for the contention that consciousness can be extracerebral may perhaps be found in the work of John Lorber, who discovered that some people with very limited gray matter can nevertheless function normally, and Karl Lashley, who found that no matter what part of a rat's brain he excised, or how much of it, the rat could still remember how to navigate a maze.
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