I’ve just learned that philosopher of science Peter Godfrey-Smith addresses my view on independently conscious brain regions in his evocative 2020 book, Metazoa: Animal Life And The Birth of The Mind.
What can we make of the fact that there are patient reports of what it is like when an entire brain hemisphere is anesthetized? I’ve held in print and here on my site that such reports indicate what it’s like for the region of the brain that continues to function while the complementary region is offline. After all, these reports appear to be reports about a consciously experienced loss, and a real experience of loss necessarily involves a real experience of how things were before the loss. Thus, the portion of the brain that remains conscious as one hemisphere sleeps was already conscious, even while the whole brain was also conscious. Consequently, the brain has some independently conscious regions, some of which overlap each other.
Godfrey-Smith offers an alternative: when one hemisphere is anesthetized, the other becomes conscious. Though I haven’t seen him remark on this (still reading), Godfrey-Smith’s view entails that this newly conscious physical entity merely seems to remember what it was previously like. Because it was not conscious prior to the anesthetization of the other hemisphere, it never did consciously experience anything; however, now during the anesthetization of its other half, it only seems to recall what that was like.
The false memory implications of this view is one reason I’ve resisted it, but they raise an intriguing question: Even if this newly conscious hemisphere has a false memory of its previously being conscious, might it nevertheless have an accurate memory of what it was like for the whole brain to have been conscious? The situation is like that of the bioengineered “replicants” in the science fiction film Blade Runner 2049 who have certain memories of events experienced by others; such a memory is false in the sense that it did not actually happen to the bearer of the memory but true in the sense that it actually happened to someone. If a hemisphere can “remember” in this sense what it was like to be a whole brain, then this would be an instance of one material thing knowing what it’s like to be another material thing, albeit an overlapping material thing.
Note that my view is open to this possibility as well. The view that the right hemisphere experiences what it is like to have and then to lose contact with the left does not necessarily preclude the possibility that the right hemisphere can also know what it is like to be the whole functioning cortex or brain, or even the left hemisphere. Perhaps these considerations of overlap and shared memories form the basis for a novel approach to answering Nagel’s question, though as I see it so far the approach seemingly requires a number of nontrivial assumptions.