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This list is about two years out of date; take a look for the long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