Brain Capacity?

Madhusudan Natarajan nutty at brain
Tue Mar 11 15:23:56 EST 1997

Dag Stenberg (stenberg at cc.Helsinki.FI) wrote:
: Kevin Spencer <kspencer at> wrote:
: > ak057 at (Shane Markle) writes:
: > >I recently heard of a calculation of the general amount of information 
: > >stored in a human brain, represented in bits, and need to know what that 
: > >capacity is.  ...

: > Whatever this number turns out to be, I wouldn't put any faith in it.
: > The brain isn't a computer based on binary logic.  It certainly doesn't
: > store information as bits.

: I applaud Kevin's comment. 

Well, even if the brain is analog, the information capacity can be 
measured in bits so to speak. If we then say that the brain's storage 
capacity is X megabytes, then we can rationalize this to be an equivalent 
statement to "the brain has enough space to store the same amount of 
information that a hard disk with a X Mb capcity can store".

The brain being analog would store information differently but the 
capacity can be measured in any form nevertheless. Just a case of scaling 
units. Of course the anlog to digital translation would imply a higher 
scaling factor of say a magnitude of order higher.

a somewhat similar analogy would be ' the power lines supplying 
electricity operate on A.C. and the average power in a sine wave (or 
cosine) is zero... but we still get power measured as rms power which is 
the amount of power that an equivalent dc voltage would supply.

Would this be an acceptible statement?

Brain has N neurons.
Each neuron has M synapses (on average).
ASSUMING that the brain is digital (which its not)
and ASSUMING that each synapse is digital (which its not/we dont know)

the least information capacity possible is M*N bits

Information capacity will obviously increase with nonlinearity of 
synaptic integration (i.e. non digital and more than two states) and 
decrease with homologous activity required to activate a threshold 
voltage (dependent upon a large number of factors like where the synapses 
are wrt spike initiation pt (1st node of ranvier)) or how many there are 
or what the concentration of receptor activators are (in cases of 
receptor mediated transfer) or what the intracellular and extracellular 
concentration of charges (i.e. voltage differences) are etc. etc.

This part is impossible to quantify, but for a start cant we say that the 
minimal capacity of the brain can be ballpark estimated (just to order of 
magnitude) by the M*N relation ?

Madhusudan Natarajan		
					..and still partly at..	
Ward 5-223 : Ph (312) 503 0202		
Dept. of Physiology			Dept. of Biomedical Engineering
Northwestern University			University of Akron

"I have no data yet. It is a capital mistake to theorize before one has 
data. Insensibly one begins to twist facts to suit theories, instead of 
theories to suit facts."    - Sherlock Holmes

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