[Comp-neuro] Review announcement

Dario Ringach darioringach at mac.com
Thu Jul 31 15:56:09 CEST 2008


A particular interesting argument about the function (actually, the  
lack thereof) of cortical column is:

Horton JC, Adams DL.
The cortical column: a structure without a function.
Philos Trans R Soc Lond B Biol Sci. 2005 Apr 29;360(1456):837-62.

--
Dario


Dario Ringach, PhD

Professor of Neurobiology and Psychology
Jules Stein Eye Institute
David Geffen School of Medicine
University of California, Los Angeles

dario at ucla.edu | http://web.mac.com/darioringach

On Jul 29, 2008, at 12:04 PM, jim bower wrote:

> ). Hi Jim (from a limo in oakland...!):
>
> Would you mind pointing me to data suggesting that cortical columns
> don't exist? That (among many others you've made, of course!) is an
> interesting point!
>
> Garrison Cottrell
>
> ---------------------------------
> Well, this started as questioning over generalized assumptions and a  
> concern with definitions -- so why not?
>
> How about this. Can anyone propose a consistent definition of a  
> cortical column?
>
> You might want to start by reading Vernon Mouncastle's original  
> paper (1958 I think), in which there was a very clear definition.   
> (Several years ago he also published a review defending, in effect  
> the original definition).
>
> If you read closely, there is actually very little evidence for his  
> original definition. However his assertion that columns represent  
> the " fundamental computational unit "of the cerebral cortex of  
> course does persist as the idea is very attractive as a way to  
> simplify and reduce complexty (and thus see previous).
>
> Here are some more specific questions:
>
> Do columns have boundaries as Mountcastle clealry believed and  
> believes? If not they are strange columns, if they don't then  
> doesn't that imply that the mapping function is continuous and not  
> discrete?  What does that imply about a functional unit?
>
> Mountcastles original observation was that neurons sampled by a  
> single electrode inserted perpendicular to the surface of the cortex  
> have the same receptive fields and represented the same subclass of  
> tactle receptors  in all layers of somatosensory cortex . This of  
> course is not true.
>
> Visual cortex however saved the day.
>
> While you can patch together a quasi-columnar pattern in V1, if you  
> try hard enough, it becomes harder and harder the further "in" you go.
>
> Personally, I believe that the belief in cortical columns is a  
> consequence of the dominance of computational and experimental   
> studies of the visual system in mammals. (The turtle 'visual' cortex  
> isn't organized this way) as well as our innate desire to find some  
> regularly repeatable and defiable simplification.
>
> The assertion that V1-like cortical columns are the funamental  
> computational unit of cerebral cortex has real difficulties if you  
> look at the olfactory system. As I suggested earlier, in my view the  
> likely "inventor" of the cerebral cortical style of computation.  
> Forcing columns into olfactory cortex is extremely difficult. For  
> sure there is a radial organization of cerebral cortex, that is  
> clear from looking at the dendrites of pyramidal cells. -  but  
> cortical columns with discrete boundaries, and containing neurons  
> with similar receptive fields (and in .ointcastles original  
> conception representing the same types or peripheral receptors or in  
> other words coding the same information about the stimulous, is an  
> excellent example of what I referred to last week as the tyranny of  
> ideas in neuroscience and computational neuroscience. Which will  
> continue in  the absence of a formal system of description and  
> definitions based on the structure of the brain itself.
>
> Jim Bower
>
>
> Sent via BlackBerry by AT&T
>
> -----Original Message-----
> From: Garrison Cottrell <gary at cs.ucsd.edu>
>
> Date: Tue, 29 Jul 2008 10:21:21
> To: <bower at uthscsa.edu>
> Subject: Re: [Comp-neuro] Review announcement
>
>
> Hi Jim (from a limo in oakland...!):
>
> Would you mind pointing me to data suggesting that cortical columns
> don't exist? That (among many others you've made, of course!) is an
> interesting point!
>
> g.
>
> On Jul 28, 2008, at 4:32 PM, jim bower wrote:
>
>> Ross
>>
>> Great -  thanks for support from an unexpected source. ;-).
>>
>> While it is completely contrary to the intuition of most
>> experimentalists who are fond of their single neuron data, it is
>> quite likely that individual neurons in at least the mammalian brain
>> don't matter. Although, as I have mentioned before, one must be
>> aware that neurobiologists pick stimuli to maximize the presumption
>> that they do.
>>
>> On the other hand, in the extreme one could find oneself arguing a
>> la Lashley that there is no structure in cortex and everything is
>> completely distributed. This is also clearly not true. I have
>> suspected for some time that the need for communication (as
>> reflected very loosly in cortical oscillations) is what detemines
>> the size of the population of neurons across which different types
>> of computations are implemented but within which, individuals
>> actually don't matter much. These populations are probably analogous
>> to cortical areas.
>>
>> One other point however, is that abstract modelers tend to think of
>> cortex as one thing and so do many neurobiologists who like to think
>> in terms of things like the cortical microcircuit (or as in the case
>> recently of the blue brain project of a cortical column, which
>> actually doesn't exist - but anyway) in fact it is likely that
>> cerebral cortex is a sequence of things. Getting at what cortex does
>> will require that we understand where this sequence starts and ends.
>> And, no time here and on my poor blackberry to discuss this, but if
>> you are trying to sort these things out in the context of the visual
>> system, as most are, you may be starting at the wrong end. It seems
>> to me likely that it is the olfactory system that invented basic
>> cortical circuitry. And there is a rather interesting story emerging
>> there about just how random cortical activity and connectivity is.
>>
>> Jim bower
>>
>> Jim
>> Sent via BlackBerry by AT&T
>>
>> -----Original Message-----
>> From: "Ross Gayler" <r.gayler at gmail.com>
>>
>> Date: Tue, 29 Jul 2008 08:07:20
>> To: <bower at uthscsa.edu>
>> Cc: <comp-neuro at neuroinf.org>
>> Subject: Re: [Comp-neuro] Review announcement
>>
>>
>> I had avoided weighing into this discussion on the grounds that my
>> interest
>> lies in abstract connectionist models that are quite remote from the
>> physiological detail that has been the focus here.  However, I would
>> like to
>> reinforce a comment that Jim Bower made.
>>
>>> the more sophisticated a coding system, the harder it is likely to
>>> be to
>> distinguish signal from "noise".
>>
>> Vector Symbolic Architectures are a family of abstract connectionist
>> models
>> that use very high-dimensional vectors to represent complex data
>> structures
>> that might be required for cognition. (Here's a quick challenge
>> question for
>> you. How might the brain represent "The astronomer believes that the
>> little
>> star orbits the big star"?)  In VSA these data structures are
>> represented by
>> the pattern of activity over, say, 10,000 neurons (abstracted as a
>> 10,000
>> dimensional vector).  This is a thoroughly distributed
>> representation in
>> which there is no necessary significance to the activity of any
>> individual
>> neuron - it is only the overall pattern of activity that represents.
>>
>> Furthermore, and this is the point I wanted to make, individual
>> patterns of
>> activity are generally indistinguishable from random vectors.  It is
>> only
>> the relationship between representing vectors that carries useful
>> information.  An external observer cannot decode the representing
>> vectors
>> without knowing what other vectors are stored in the clean-up memory
>> of the
>> system.  I take these representations to be a very clear
>> demonstration of
>> Jim's point that in a sophisticated coding system it is harder to
>> distinguish signal from noise.
>>
>> This paper (http://cogprints.org/3983/) provides some pointers into
>> the VSA
>> literature.  The most extensive treatment of a specific
>> instantiation of VSA
>> is Tony Plate's book
>> (http://csli-publications.stanford.edu/site/1575864304.html)
>>
>>
>> Ross Gayler
>>
>>
>>
>>
>> -----Original Message-----
>> From: comp-neuro-bounces at neuroinf.org
>> [mailto:comp-neuro-bounces at neuroinf.org] On Behalf Of jim bower
>> Sent: Saturday, 26 July 2008 7:31 AM
>> To: rod rinkus; comp-neuro-bounces at neuroinf.org; minai_ali at yahoo.com
>> Cc: comp-neuro at neuroinf.org
>> Subject: [Possible Spam] Re: [Comp-neuro] Review announcement
>>
>> One last plea for caution. No matter how convenient "noise" may be  
>> for
>> abstract models, one can argue I think pretty convincingly that life
>> itself
>> differentiates itself from a-biological chemical evolution through
>> its use
>> of extreme degrees of structure and context specific organization to
>> "beat"
>> thermodynamics.
>>
>> As such anything that smells gaussian, disordered, something you can
>> average
>> over, or something that is completely generic rather than highly
>> specific to
>> the circumstances at hand (behavioral or computational) should raise
>> concern.
>>
>> The long history of biology is that the closer you look, the more
>> structure,
>> not less structure you see.  And everytime I have heard it suggested
>> otherwise, closer inspection has suggested that we simply weren't
>> giving
>> biology enough credit.
>>
>> One quick example, a number of years ago, in fact during the first
>> summer of
>> the first computational neuroscience course in woods hole, a well  
>> know
>> investigator of aplesia neurons gave a general MBL talk in which he
>> sought
>> to identify every conductance in the neuron of interest. In addition
>> to the
>> big "important" ones he found several small ones, whose presence he
>> chalked
>> up to sloppyness in protein transcription.
>>
>> Given my predispositions, I suggested that he change the temperature
>> of the
>> bath as aplesia live in tide pools. The next summer he gave a talk
>> on the
>> remarkable resiliance of neuronal function under different ambient
>> temperatures confered by the complex conductances present in the cell
>> membrane.
>>
>> While convenient, many of these "noise" mechanisms strike me as
>> being simply
>> not sophisticated enough. And I will point out now for the last
>> time, that
>> the more sophisticated a coding system, the harder it is likely to
>> be to
>> distinguish signal from "noise".
>>
>> Jim Bower
>> Sent via BlackBerry by AT&T
>>
>> -----Original Message-----
>> From: "rod rinkus" <rinkus at comcast.net>
>>
>> Date: Thu, 24 Jul 2008 00:33:59
>> To: <minai_ali at yahoo.com>
>> Cc: <comp-neuro at neuroinf.org>
>> Subject: RE: [Comp-neuro] Review announcement
>>
>>
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>
>
> Gary Cottrell 858-534-6640 FAX: 858-534-7029
> Computer Science and Engineering 0404
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> "Only connect!" -E.M. Forster
>
> "I am awaiting the day when people remember the fact that discovery
> does not work by deciding what you want and then discovering it."
> -David Mermin
>
>
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