X-Message-Number: 26775
Date: Sun, 7 Aug 2005 09:38:56 -0400
From: Thomas Donaldson <>
Subject: new neurons and new methods

Hello Appraisco!

It's very likely true that most neurons remain for a long time. However
it's not clear at all from your article that the measurements made
by Dr Frisen of brain cell neurons will take account of the formation
of new neurons as a minority of neurons. Moreover, our visual cortex
is likely to be a brain area which really does take a more permanent
form when we're young. Elizabeth Gould did not propose that our neurons
underwent a total turnover, either; just that some new neurons occur
in all of our cerebral cortex even when we're adults.

It's particularly regretable that Frisen did not look at generation of
new neurons in our hippocampus, where virtually everyone agrees that
this happens. Apparently for monkeys, unlike rats or mice, new neurons
migrate from the areas in the supraventricular surface (a skinlike
surface surrounding a connected area in our brain filled with 
ventricular fluid) to many different areas in our brain. In rats and
mice they almost entirely migrate to the brain areas dealing with
smell.

It's also very unlikely that we get a new neuron(s) for every new
memory. At that level we'd probably see growth of new synapses
connecting different neurons, rather than whole new neurons. Still,
even new neurons will eventually be needed if memories to be stored
increase as we continue to live.

It would be nice if you had given a full, explicit reference in your
message. I will do my best to find the original scientific article
by Frisen et al in CELL. As for new neurons, it's by now quite
clear that we form new neurons. The technique used by Frisen suggests
that we'll be soon able to find out just where new neurons go and 
how many there may be.
    
            Best wishes and long long life to all,

                 Thomas Donaldson

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