Few long-standing questions about neocortex

Viktor Kharazia kharazia at POBOX2.STANFORD.EDU
Mon Mar 9 19:05:37 EST 1998


To Ron Blue and OhGeeJody, thanks for your very informative messages. I am
glad that there is some enthusiasm in this area. 
Hopefully, that my own sketchy thoughts on those old-fashion questions will
not be interpreted as another example of the obsessive compulsive... It is
just a few innocent points. Constructive critique, however, is welcome.

1. What is the function of the neocortex? Why it is so prominent in higher
mammals?
Evolution of nerve systems (I believe there is a such thing), have acquired
a strong potential (force, if you wish) when nerve cells (together with
glia) were turned from what could be as an optional path to a true
determination to use amino acids, especially glutamate for signaling. It
has happened everywhere in nervous system, but cortex is among few places
which come as "fully" glutamateergic systems. GABA is a derivative of
glutamate, appeared to be used only within local intracortical circuitry.
The function of neocortex, or even parts of it, may not be accurately
stated, on my opinion, probably because of its intense ongoing "horizontal"
evolution. Mammals have this expansion of superficial layers 2-4,
innervating nothing but each other or themselves. Cells in deeper layers
also have a good deal of interconnectivity, but project also to the other
places, like spinal cord or thalamus. As another side of this process,
primates compared e.g. to rodents appeared to have less significant role
for interneurons on a periphery of the nervous system that receive cortical
fibers(e.g. spinal cord). It is looks like what a cephalization might
reflect in general: to accumulate more responsibilities in one place...
2. Is there a foundation of the human intelligence in the neocortex? If it
is, where it might be?
I am not comfortable to elaborate on nature of human intelligence. This
issue seems (1) overly complicated, (2) getting away from neurobiology to
AI people. I believe there has to be a cortical type of intelligence that
can be described as a biological phenomenon. If it is true, cortical
intelligence might be a delayed result of the cortical evolution; delayed
means that some useful features of neocortex were utilized immediately upon
its emerging (sensory/motor) which have allowed to these species to advance
on a face of the Earth; some features were unfolded later (associative:
complicated behavior, speech, intelligence, schizophrenia), some may be yet
to come.... Where in the cortex these "things" may develop: in "younger"
superficial cortical layers, which known to have only (ONLY) intracortical
connections.
3. Is the anything really unique about cerebral cortex? Something, that
can't be found anywhere else.
-Quite a lot.  I just mentioned one feature, which might be characteristic
of the neocortex: vast number of cells that do not project to outside
structures. They are interconnecting various areas of the cortex, that is
the only we can think they might do. Another obvious thing: all (!) axons
that come from the cerebral cortex (corticofugal) use only excitatory amino
acids as neurotransmitter. No other brain structure in mammals appeared to
have a such uniformity. However, it may not be true in the future.

VK







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