Extending the lifespan: problems and questions

William Calvin wcalvin at hardy.u.washington.edu
Tue Apr 28 18:31:58 EST 1992

Here are the references from the endnotes of my 1990 book, The Ascent
of Mind:  Ice Age Climates and the Evolution of Intelligence (Bantam):

226   Pruning of connections in cerebral cortex is reviewed in The
      Cerebral Symphony, p. 165, 362.  The loss of neurons is from
      J. B. Lohr and D. V. Jeste, "Studies of neuron loss with age in
      three different brain regions in humans," Society for Neuroscience
      Abstracts 15:22 (1989).  For monkey motor cortex, see J. Tigges,
      J. Herndon, and Alan Peters, "Neuronal changes in Area 4
      during the life span of the rhesus monkey,"  Society for
      Neuroscience Abstracts 15:259 (1989); they report that this
      movement control area of the leg loses nearly a third of its
      neurons between infancy and early adulthood [my wife suggests
      that the monkeys must have killed off their clumsy neurons!].

      The illustration of synaptic density in visual cortex uses the
      human data of P. R. Huttenlocher, "Synapse elimination and
      plasticity in developing human cerebral cortex."  American
      Journal of Mental Deficiency  88:488-496 (1984).  The monkey
      data is from P. Rakic, J.-P. Bourgeous, M. F. Eckenhoff, N.
      Zecevic, and P. Goldman-Rakic, "Concurrent overproduction
      of synapses in diverse regions of the primate cerebral cortex," 
      Science 232:232-234 (1986).  I have replotted the data to
      normalize peaks and used a logarithmic time scale starting at
      about 120 days after conception and ending about ten years after
      birth.  In addition to breaking synapses and withdrawing axon
      collaterals, there is also some cell death in cerebral cortex during
      the same period.  The lateral shift in the human curve relative to
      the monkey curve would be consistent with a two- to three-fold
      slowing of human somatic development.

This list is about two years out of date; take a look for the long
articles based on those abstracts from 1989.

    William H. Calvin   WCalvin at U.Washington.edu
    University of Washington  NJ-15
    Seattle, Washington 98195 FAX:1-206-720-1989

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