““Is Your Brain Really Necessary?”, Revisited”, 2015-07-26 (; similar):
According to British biochemist Donald R. Forsdyke in a new paper in Biological Theory, the existence of people who seem to be missing most of their brain tissue calls into question some of the “cherished assumptions” of neuroscience. I’m not so sure.
…There’s no question that some of these brains are very striking. But I don’t think we need to throw out the textbooks yet.
While the enormous “holes” in these brains seem dramatic, the bulk of the grey matter of the cerebral cortex, around the outside of the brain, appears to be intact and in the correct place—this is visible as the dark grey ‘shell’ beneath the skull. What appears to be missing is the white matter, the nerve tracts that connect the various parts of the cerebral cortex with each other, and with the other areas of the brain. However, some white matter is still visible as the pale grey layer that borders the holes. The big question is whether this layer of white matter is sufficient to connect up the grey matter and allow it to function normally. There doesn’t seem to be much of it, but on the other hand, we really don’t know how much white matter is strictly necessary.
I wonder also if the white matter might be denser than normal ie. if the fibers were packed together due to being gradually compressed by the expanding fluid spaces? No-one seems to have looked at this possibility directly; while there have been brain scanning studies of these adult post-hydrocephalics, no detailed post-mortem studies of their brain tissue have been published, as far as I know. (Forsdyke does not discuss any and I couldn’t find any in my searches.) For more on the neuroanatomy of this issue, see John Hawks (discussed by Forsdyke.)
Therefore in my view, these cases probably won’t require us to rethink neuroscience, although they do raise the issue of how much white matter is necessary. It may be that much of our white matter is redundant, which would be interesting, but not on a metaphysical level.