[Comp-neuro] Review announcement

jim bower bower at uthscsa.edu
Tue Jul 22 11:50:37 CEST 2008


And I have a fairly simple question in return. Does anyone know of any type of engine, computational or other that is as thermodynaically efficient as the nervous system?  Burns glucose, has 10 to the 12th neuronal components and doesn't generate enough heat to keep itself warm. Given that level of efficiency, why wouldn't you expect optimality. 

Second question, is there any case where it has or can be measured that the nervous system doesn't opperate at or very near physical limits, single photon detection, quantal limits in electrorecptors, just over brownian noise in the auditory system, etc. Why wouldn't one expect similar levels of performance computationally. 

Next, if spike coding in the nervous system were at optimal efficiencies, what would you predict?  Signal indistinguishable from noise. 

Finally, there is no taskmaster as rigorous or demanding as selection. We tend not to think so - but this is mostly wishful thinking. The history of neuroscience and computational neuroscience is full of examples where "smart" practitioners have declared one or another aspect of the nervous system to be less than optimized only to find out that they simply weren't asking the right question or didn't understand themselves the circumstances or real computational demand. 

Jim Bower
Sent via BlackBerry by AT&T

-----Original Message-----
From: "Hans A. Braun" <braun at staff.uni-marburg.de>

Date: Tue, 22 Jul 2008 11:32:54 
To: <bower at uthscsa.edu>; Nathan Urban<nurban at cmu.edu>; <comp-neuro-bounces at neuroinf.org>; <comp-neuro at neuroinf.org>
Subject: Re: [Comp-neuro] Review announcement


Hi Jim,



nice to hear from you with an interesting question. Here is a question back:

Who says that the biological coding scheme is optimised in a way as
engineers would do?



I have been educated as an engineer. Thereby, I specifically have learnt how
handle, if it cannot be avoided, such detrimental system properties like
noise, nonlinearities and time delays because these can lead to
unpredictable system behavior, including undesired oscillation and chaos –
what regularly can be seen in all kind of biological systems. If something
similar would happen in a car or an airplane, the responsible engineer,
deservedly, would immediately be fired.



Could it be that the engineer in evolution has used a principally different
strategy?

What was/is his/her goal?

Who knows or who is interested to find the answer?

- or a more appropriate question ;-) ?



Coming back to the original "noise" question: During all the years as
experimental physiologist I have got hundreds of hours recordings of impulse
sequences from different neurons – and all look more or less noisy -
whatever it means.



Best wishes

Hans Braun



PS: if you are interested, here are two references to our work (an actual
and an earlier paper):



Finke C, Vollmer J, Postnova S, Braun HA (2008) Propagation effects of
current and conductance noise in a model neuron with subthreshold
oscillations. Mathematical Biosciences doi:10.1016/j.mbs.2008.03.007

Braun HA, Wissing H, Schäfer K, Hirsch MC (1994). Oscillation and noise
determine signal transduction in shark multimodal sensory cells. Nature 367:
270-273.



The first one is a mathematical/computational approach which has very
recently been published, so far only as online version.

The second reference is to a much earlier experimental paper which
demonstrates how the evolutionary engineer might have used oscillations and
noise to achieve a particular sensitivity. This strategy, for whatever
reasons, was only realized for sensory encoding in some evolutionary very
old animals like sharks.

Dr. Hans A. Braun, Institute of Physiology, Deutschhausstr. 2, D-35037
Marburg, Germany.
Tel: +49 (0)6421-286 23 05, FAX: +49 (0)6421-286 6967, E-mail:
braun at staff.uni-marburg.de
URL: http://www.uni-marburg.de/physiology/braun and  http://www.clabs.de
see also: http://www.BioSim-Network.net

----- Original Message -----
From: "jim bower" <bower at uthscsa.edu>
To: "Nathan Urban" <nurban at cmu.edu>; <comp-neuro-bounces at neuroinf.org>;
<comp-neuro at neuroinf.org>
Sent: Friday, July 18, 2008 3:56 PM
Subject: Re: [Comp-neuro] Review announcement


> Haven't done this in a long time. But who says neurons are noisy?
>
> From the point of view of information theory, why isn't the apperance of
noise expected in a highly optimized coding scheme?  And why isn't synchrony
to be avoided as redundency. Engineers avoid it, why shouldn't evolution.
>
> Just curious.
>
> Jim bower
> Sent via BlackBerry by AT&T
>
> -----Original Message-----
> From: Nathan Urban <nurban at cmu.edu>
>
> Date: Fri, 18 Jul 2008 08:41:22
> To: <comp-neuro at neuroinf.org>
> Subject: [Comp-neuro] Review announcement
>
>
> Review announcement
>
> This review describes a constructive role for noise in synchronizing
> populations of neurons and should be of interest to computaional
> neurosciuentists.
>
>
> Trends Neurosci. 2008 Jul 4. [Epub ahead of print]
>     Reliability, synchrony and noise.
>     Ermentrout GB, Galán RF, Urban NN.
>
> The brain is noisy. Neurons receive tens of thousands of highly
> fluctuating inputs and generate spike trains that appear highly
> irregular. Much of this activity is spontaneous - uncoupled to overt
> stimuli or motor outputs - leading to questions about the functional
> impact of this noise. Although noise is most often thought of as
> disrupting patterned activity and interfering with the encoding of
> stimuli, recent theoretical and experimental work has shown that noise
> can play a constructive role - leading to increased reliability or
> regularity of neuronal firing in single neurons and across populations.
> These results raise fundamental questions about how noise can influence
> neural function and computation.
>
>     PMID: 18603311 [PubMed - as supplied by publisher]
>
>
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T0V-4SXC918-1&_us
er=525223&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000026389&_versio
n=1&_urlVersion=0&_userid=525223&md5=22a86291fe13cd59541d841f692f24a2
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