X-Message-Number: 27560
Date: Thu, 2 Feb 2006 07:37:58 EST
Subject:  Uploading (3.iii.1) How much ressources ?. 

Uploading (3.iii.1) How much ressources ?.

From time to  time, I add to this message set about brain on electronics 
devices, the (3.x.y)  subfamilly is more technology oriented. One preceeding 

conclusion was that some  fast process must be worked out by FPGA and slower 
by computers. I would  add another divide: Classical artificial neurons work 
only by firing or not.  This is defined by the summed up potentials from 

postsynaptic domains. If this  sum is larger than a threshold the neuron fire, 
if it 
is under it does nothing.  There is a hidden assumption in this : A start, the 
neuron is at its equilibrium  potential. In a real neuron this is a unlikely 
assumption because there are many  subthreshold activities in many dendritic 
domains. This add up to a local, ie  intraneuron, noise reducing the potential 
jump requested to fire. There is  another general, ie interneuron, noise 
produced by electric gap  juctions.

In a microcolumn with up to some hundreds cells, the  electrical links may be 
so strong that coordinated behavior may be the rule. On  the onther side, 
from one microcolumn to another, most links seem to be done by  axons. So the 

artificial model in current use would be  a good fit for  microcolumn links and 
bad one for individual neurons in a given microcolumn.  This give the idea to 
have two different electronics neurons: One equivalent to  a biological one 
and another, a metaneuron, for a full microcolumn. In a first  approximation, 
the metaneuron could be somewhat frozen in behavior, so it would  give a 

defined answer to a given input. This would be actualised by the deeper  
level, but this one would be done only on a sample of the information  

Assume there is 10 billions neurons divided into 30  millions microcolumns. 

The brain simulator would use 30,000,000 metaneurons. If  each is redefined one
time every ten seconds, an electronics system able to work  out a full 

microcolumn in 1 000 000 clock cycles could oversee  five thousand metaneurons 
if it 
run at 500 MHz. This frequency seems the  highest in current day FPGA. So, 

only six thousand such cards could handle the  basic brain working at elementary
level. This is somewhat optimistic as the  rewiring time is not taken into 
account. The real value may be two to three  times larger. 

Because the signal to a metaneuron needs to travel in something as 100  
neurons, it can't be faster than one percent of the fastest signal in an  

individual neuron. If this is put at one millisecond, the metaneuron works at  
the 100 
ms scale. This is indeed typical of the fastest reaction time in the  brain. 
There must be a security margin: some signal may travel in a small  subsample 
of a microcolumn. So the signal may be faster, particularly after  training. 
The metaneuron may be actualised every ten miliseconds. Assume again  500 MHz 
clocking and 100 clock cycles to do the job on one metaneuron every 10  ms. 

50,000 metaneurons could be simulated in a time sharing system. This  would 
600 chips for a full brain with 30 millions metaneurons. Again, this  don't 
take into account the rewiring time. This can ask for x3 more material  

We have identified four processing here: The basic neuron fast current  

processed by a computer, the basic neuron slow one taken into account by an  
the basic neuron local and global nonfiring activity, using gap junctions  and 
the metaneuron, without gap junction nor slow/fast current  division.

In a first simulator, ASIC (custom made Application  Specific Integrated 
Circuit) and TRACs must be put on the side, because they are  too costly to 
produce and ask for too much work. That let only classical FPGAs  and general 
purpose computers.

Yvan  Bozzonetti.

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