Extending the lifespan: problems and questions

William Calvin wcalvin at hardy.u.washington.edu
Mon Apr 27 21:42:23 EST 1992

allens at yang.earlham.edu (Allen Smith) writes:

>In article <1992Apr25.050012.29709 at u.washington.edu>, wcalvin at hardy.u.washington
>   .edu (William Calvin) writes:
>> The issue probably revolves around whether the brain could continue to
>> learn new information (at least, in a way that could still be retrieved
>> efficiently) if the lifespan doubled.  There is one line of evidence that
>> information is stored by something of a carving process, where if you keep
>> adding things, you are in some danger of running out of synapses to carve.
>>    Between 8 months of age and puberty, we lose 30-50% of our synapses in
>> cerebral cortex.  The trend is downhill in adulthood, but there isn't too
>> much good data yet (and we don't really know what it means, either).  I
>> discuss this a bit about p.190 of my book THE ASCENT OF MIND (Bantam
>> 1990), and there is a graph of the synapse decline with age in man and monkey.

>        In other words, the number of synapses (as opposed to brain cells)
>goes down as one gets older? Then why does "fixed" IQ increase with age?
>Is this decline simply due to loss of neurons, or what?
>        If we're going to really stop aging, then we'll need to figure out
>how to get neurons to regenerate. Some clues can probably be found in the
>nasal neurons (which keep dividing); what's the current status of research
>on the cause of this difference?
>        -Allen

IQ has a lot to do with the speed of processing, and the number of things
that you can "hold in mind" simultaneously (as in doing an
analogouis-reasining task, or digit span, etc.).  I doubt that either is
greatly affected by the sorts of 10-20% losses of synapses in adulthood
that we're probably talking about.  Now if the losses from puberty to age
70 reached 80%, as they do in some subcortical regions (substantia nigra),
then you'd probably see trouble.  That's what we might get into, with a
130 year life span.
   W. H. Calvin

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