IUBio

Afferent data rates

Konrad Weigl weigl at sibelius.inria.fr
Fri Aug 16 03:46:31 EST 1991


In article <HUNTER.91Aug14150200 at work.nlm.nih.gov>, hunter at work.nlm.nih.gov (Larry Hunter) writes:
> 
> I think it might be simpler to consider an action potential (or lack
> thereof) as a single message.  That way, a neuron has 2 output states,
> and the time it takes to transmit a single message is the period
> between action potentials when the cell is firing at its maximum rate.
> Since S is 2, this reduces to 
> 
>   I = N/t = Nf
> 
>   where f = maximum firing frequency of a neuron, as action potentials/second.
> 
> Granted, this ignores signal propagation via voltage changes that are
> not sufficient to generate action potentials.  There is some evidence
> that this mode of transmission may be important, but let's skip that
> for the time being.
> 
> So, in yet another attempt to rephrase my question:
> 
> 1. How many sensory neurons are there in an adult human being?
> 
> 2. What is the maximum firing rate of a neuron?  If this varies among
>    populations of neurons, what is the distribution of maximum firing
>    rates? 

I'm not a neurophysiologist.  So I don't know what an action potential is,
but I assume it is what is commonly called a _spike_.

If that is the case, then you can certainly compute the possible maximal 
information _transfer_ rate between successive layers of neurons as described;

however, this does not imply anything about the maximal information
flow a layer of neurons would have to deal with, but can only give an
_absolute_ upper limit for that flow.  

This is so since computation by neurons take place through detection of 
correlations between incoming spike trains, as far as I know;

If we consider individual, uncorrelated spikes as messages, we ignore:
a) the correlation between spikes coming in simultaneously from
different sources, and b) the integration of spike trains.

the effective maximal information _processing_ rate could thus be much lower.

(Note that the term _information_ is seen here context-free, in the information-
scientists' sense; thus could be misleading here; the term data would be 
better, since, IMHO, information, in the biological sense,  presupposes an environment where _data_ has __meaning_, and thus can be interpreted as _information_; the same caveat, obviously, applies to the term _information_ 
transfer rate; _data_ transfer rate might be more suitable)



Konrad Weigl               Tel. (France) 93 65 78 63
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