[extropy-chat] Longevity Meme: Activism for Healthy Life Extension

[Robert J. Bradbury]

On Thu, 27 Nov 2003, Adrian Tymes wrote:

Commenting on 2000-7000 year life spans...

> Or scientists who don't want to overly future shock
> the public, fearing they might lose their jobs if
> they did.

Well, if they are short-changing reasonable expectations
intentionally then IMO its a form of fraud.

Commenting on neuron loss...

> And can be regenerated, it turns out.  It was once
> thought otherwise, but apparently not so.  Of course,
> it might be the case that the natural replacement rate
> is less than the natural death rate, but this is
> something we can adjust.  (Or, as you suggested, do
> replacements.)

There is limited regeneration in the hypothalmus I
believe (Anders correct if this is wrong) but not
in the cerebral cortex.  See [1].

> You can't even get away with 100%.  People usually
> don't lose too many brain cells between 10 and 20 and
> 30, yet people are often at least a little - sometimes
> (often?) significantly - different at those ages.

Well between 10 and 20 there are well documented hormonal
changes causing neuronal structure/activity changes.
Between 20 and 30 I would submit that it probably has
to do with the rapid accumulation of "life experience"
rather than brain cell gain/loss as a primary driving
force.  But it seems to be the remaining years during
which one experiences gradual loss.  According to the
abstract for [1], the loss is 10% from 20 to 90.  I'm
sure you can do the math.

Robert

1. Pakkenberg, B. & Gundersen, H. J. G., "Neocortical Neuron
   Number in Humans: Effect of Sex and Age", J. of Comparative
   Neurology 384:312-320 (1997);
   http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9215725&dopt=Abstract
   (Pakkenberg has a number of other studies related to this in PubMed).