Neuroanatomy again

Generally I try to do 2 posts a week but I also farm for two markets a week and my time and energy is limited during this part of the year.  I saw interesting news this week on several fronts and will talk about agenesis of the corpus callosum today (and genetic studies of hunter/gathers vs agriculturalists and meditative brains later). reported a study showing that  people with callosal agenesis actually have other rather disorganized fibers connecting each hemisphere.


Some few people are born without a corpus callosum.  Evidently the fibers develop in the fetus longitudinally in their respective hemispheres and do not cross over, yet these people have few, if any, mental sequelae.  Recent anatomical studies show that in these patients some fibers do cross over, not in any massive or organized manner, but sufficient to facilitate inter-hemispheric integration.  One of the truisms that I do not think gets much mention is that peoples’ anatomies vary across individuals a good deal and yet we all function about the same.  I have a colleague with congenital prosopagnosia, the inability to recognize faces; she can sit next to an acquaintance or ride with a familiar in an elevator without recognizing them unless they speak and she can recognize their voice. Some suffer from this due to stroke but she was born this way and does quite fine, even if she does have to apologize or explain sometimes why she seemingly ignored someone’s presence.  Anyway, we all have variations in our brains, organs, skeleton, and musculature etc not listed in the anatomy books.

Back to the corpus callosum.  Back in the 1960s, Roger Sperry and Michael Gazzaniga studied patients who had had their corpus callosums cut in order to control otherwise intractable epilepsy.  These patients generally show very little consequent dysfunction but with careful experimental procedures, they found that the two hemispheres carry on independent functions unknown to the other, i.e., they each seem to have their own consciousness.  I will not go into detail as so many are familiar with them but these are very interesting studies, so well done, and illustrative of good science and medicine running together.


Now I decided to re-read Julian Jaynes’ book from way back then, The Origin of Consciousness in the Breakdown of the Bicameral Mind, for a variety of reasons.  I am finding I still disagree with him a good deal (and will address this in a future post) but he summons a great deal of scholarly information and scientific data that is interesting and informative.  He gives an excellent summary of the split brain research as he seeks support for his idea that the two hemispheres function very differently from each other.  He focuses on the findings that both hemispheres understand speech while only the left one produces speech, and goes from there with various stops along the way to say the right hemisphere spoke internally and that these were the voices of the gods helping ancient humans figure things out and solve problems of action.  Is this a biological root of religious beliefs?  Jaynes thinks further that until this neurological organization broke down, humans were not truly conscious.  Ah, well. More later but here is another view of hemispheric lateralization, left and right.


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