Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!mit-eddie!media-lab!minsky
From: minsky@media-lab.MEDIA.MIT.EDU (Marvin Minsky)
Newsgroups: comp.ai.neural-nets
Subject: Re: Postulates on the number of neurons
Message-ID: <4311@media-lab.MEDIA.MIT.EDU>
Date: 11 Dec 90 06:08:20 GMT
References: <1990Dec11.040646.20760@noose.ecn.purdue.edu>
Reply-To: minsky@media-lab.media.mit.edu (Marvin Minsky)
Organization: MIT Media Lab, Cambridge MA
Lines: 26

In article <1990Dec11.040646.20760@noose.ecn.purdue.edu> muttiah@welsh.ecn.purdue.edu (Ranjan S Muttiah) writes:
>
>What do researches think about why there are so many _individual_ neurons  
>in the human brain (something like 10^19) ?

No one thinks that.  More like 10^11.  (Many of them are little
"granule cells" with few conections.)  William Calvin mentioned
neurologist's joke: the brain contains 10 billion beurons, of which
100 billion are in the cerebellum.

It would seem likely, at least to me, that most single cells don't do
useful operations alone, so that, for example, it might need a whole
cluster or column of cells to do some little useful job.  So for many
functions, you'd be left with "only" a few hundred million" "units".
And it would seem that an ordinary "commonsense database" semantic
network might well require a few dozen million nodes and connections.
No one knows that yet, of course.

At the other end of the opinion spectrum are theorists who suggest
that each single cell might store hundreds, or even millions of bits
inside the cell.  No one has made a good case for this, or for how
they might be read-in or -out, but it certainly isn't inconceivable.

But there simply aren't enough grams of brain for 10^19 cells, or anything of
that magnitude.  Each neuron is a few micrometers in diameter, so
10^18 of them would be meters in diameter.