[Comp-neuro] The sniffing brain and free will
bower at uthscsa.edu
Mon Aug 18 20:49:49 CEST 2008
First: "Greetings, an i´ll keep reading you because you are an
authority in computational neuroscience."
Don't do that!!! -- In the interest of full disclosure perhaps I
should have explicitly stated some time ago, for those of you who
don't already know, that my views including those on the evolution of
cerebral cortex are not shared by the majority of my colleagues :-),
although also, in full disclosure, I am far from the first person to
suggest a role for olfaction in cortical evolution (in fact, I would
say that it is kind of obvious). So if you want to read an
"authorized authority on computational neuroscience" you should stop
reading now!! There are lots of excellent sources written by people
who want that kind of authority. I am less of an authority than
simply someone who for some reason (low GABA) doesn't mind rocking the
Anyway, if you are still reading, it is not about what came first,
locomotion or olfaction. All things I am aware of locomote, olfact,
sense light, etc. The argument is that 3 layered cortex came before 6
layered cortex (i.e. neocortex), and that 3 layered cortex evolved
originally in the context of the olfactory system.
Movement dictated the organization of various aspects of the spinal
cord. Neo-cortical 'movement control centers' if that is what they
are, where built on top of the more fundamental spinal chord
mechanisms (I realize that kind of statement is reckless BTW).
To vastly, vastly simplify the evidence and summarize what in fact I
hope will be a book soon, the fore-brain of the earliest vertebrates
(at least represented by modern examples -- which does, of course,
have its own problems) consists of a 3 layered cortex receiving input
from the olfactory bulb, which then in turn projects to a 'multi-
modal' cortex mixing up inputs from other sensory systems (vision,
audition, somatosensation, etc). As one moves "up" the phylum, what
one can suggest (if predisposed to be troublesome) are 'pre-
processing' areas emerge that are (largely) sensory system specific.
Even these sensory system specific areas, however, in non-mammals,
share with the olfactory system, the fact that the sensory input
contacts pyramidal cells in layer I, and spreads across the cortex
(for example in turtle 'visual' cortex) rather than the pattern in
neocortex, where the input comes vertically into layer IV. In 6-
layered Neocortex, which is largely a mammalian invention, the input
comes into layer IV although recent studies have suggested that the
inside to the outside system of layer I efferents in neocortex has a
pretty dramatic effect on cortical processing. Our neo-cortical,
layer IV, feedforward, vision system dominate approach to studying the
cerebral cortex has meant that this input was not considered for many
years (gee it's far from the soma too) and is not considered to this
day in most abstract models of cortical function. It also posses
rather significant problems for the idea of the computational
independence (or I would claim existence) of cortical columns In my
view of the world (distorted), this input should actually be seen as
the historical input to cortical circuitry, So, what does this view of
cerebral cortical evolution change:
1) it is the highly interconnected 'associative' networks of 3 layered
cortex (or IT for that matter), and not the much later evolved (pre-
processing) stages of areas like VI, with their stronger vertical
organization, that should be considered 'architypical cortex'. Thus
the fundamental organizational (computational) structure of cerebral
cortex is horizontal, not vertical, and thus has nothing to do with
2) VI and other primary sensory areas are not the first evolved by the
last evolved in the inside out evolution of cerebral cortex - thus VI
of the rat and VI of the monkey are much further removed from each
other, evolutionarily than is enterhinal cortex in either animal
(therefore explaining, I think, the rather remarkable differences in
organization of VI in different mammals).
3) Cerebral cortical evolution has not been dictated by the
computational problem faced by vision, or any other neocortical
sensory system -- but instead the 2-D relatively local style of
computation appropriate for vision has been adapted to the more
universal (gestault) type processing intrinsic to olfaction - the
early stages of visual processing in cortex are basically pre-
processing stages to adapt visual data representation into something
more appropriate for processing in an olfactory style. I doubt that
birds, whose 'higher processing region" is more likely derived from
the geniculate and thus a visual oriented style of processing, for
example "think" of trees as being one kind of thing - this kind of
grouping is the sort of thing that the olfactory system has to do, and
not the kind of thing that the visual system fundamentally cares about
(but happy to use once the olfactory system invented it).
4) it is silly to hope to understand 3-layered cortex, like the
hippocampus or enterhinal cortex, or even IT, using visual stimuli.
(I have always been amused when I visit most (with only a couple of
exceptions - Howard Eichenbaum being one) hippocampal labs at the
graduate students with alcohol rubbing down their mazes between runs,
to make sure that there are no olfactory cues left by the previous rat.
5) Similarly for frontal neo-cortex.
6) it makes no sense to me at all that for every one modeler,
experimentalist, anatomist, cognitive type, or brain imager studying
olfaction (in some cases only 1), there are 100s studying vision. One
might almost suspect that we are the odd mammal that believes (note
believes) that the visual system is really really important. Why
would that be? :-) I raise horses - you can cover their eyes and
they don't care - but mess with their nose -- trouble. (BTW, in our
textbooks, vision is represented by multiple chapters in the front of
the book, while the olfactory system usually gets about 5 pages
somewhere in the back -- odd reflection of the number of cerebral
cortical areas associated with each).
7) There's lots of stuff we won't ever understand (cortical
oscillations, slow wave sleep, the functional structure of pyramidal
cell dendrites, human cognition and strange stuff like meditation
(see previous reference to our recent TINS article), without first
understanding or at least considering the olfactory system.
A practical example: Charlie Grey, whose paper with Wolf Singer was
one of two responsible for neuroscientists and theorists becoming
interested in cortical oscillations opened his recording filters to
look for 40 Hz in visual cortex because he had been a graduate student
with Walter Freeman studying the olfactory system. Unfortunately most
thus turned on to oscillations have yet to leave neo-cortex or its
surrogate, the thalamus (sigh)).
On Aug 16, 2008, at 11:34 AM, anibalmastobiza at terra.es wrote:
> Ok. Dr. Bower.
> But if we frame the issue in an evolutionary timescale is it not
> better to focus on the machinery responsible for movement and the
> valuations needed to choose the apropiate course of action
> available. Because its more pertinent if we would like to talk about
> the computations underlying "free will" or cognitive freedom.
> I think even before the evolution of our magificent sense of smell
> is earlier the biological mechanisms for movement (sensory neurons,
> motoneurons, interneurons...) so it is even better to look at the
> way the spinal cord computes.
> Greetings, an i´ll keep reading you because you are an authority in
> computational neuroscience.
> Greetings to all.
> Ahora también puedes acceder a tu correo Terra desde el móvil.
> Infórmate pinchando aquí.
> Comp-neuro mailing list
> Comp-neuro at neuroinf.org
Dr. James M. Bower Ph.D.
Professor of Computational Neuroscience
Research Imaging Center
University of Texas Health Science Center -
- San Antonio
8403 Floyd Curl Drive
San Antonio Texas 78284-6240
Main Number: 210- 567-8100
Fax: 210 567-8152
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