Neural Darwinism
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The term Neural Darwinism is used in two different ways. In one usage it is the theory that consciousness can be explained by Darwinian selection and evolution of neural states. In the other it describes a process in neurodevelopment where synapses which are being most used are kept while least used connections are destroyed or 'pruned' to form neural pathways.
Although it was believed until 1998 that neurodevelopment ceased at the end of adolescence, there is now strong evidence that neurodevelopment continues throughout adult life.
Given this evidence, the two usages can be regarded as complementary, because:
- persistent patterns of neural activation (which seem to correspond to short term memory) appear to influence neural growth, death, and synapse formation, which appears to be the mechanism for the laying down of long term memory.
- patterns of neural connectivity in turn provide the substrate for patterns of neural activation
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Neural Darwinism in theories of consciousness
The term originated with Gerald Edelman's 1987 book Neural Darwinism. The Theory of Neuronal Group Selection.
It has been suggested that Friedrich Hayek had earlier proposed a similar idea in his book The Sensory Order: An Inquiry into the Foundations of Theoretical Psychology, published in 1952.
Other leading proponents include Daniel Dennett and William H. Calvin.
Neural Darwinism in neurodevelopment
The human brain rapidly creates synaptic connections between neurons after birth. The total number of synapses peaks at around 6-8 months of age. At this point the brain has approximately twice as many synapses between than will exist when the child reaches 10 years of age. Synapses are selectively destroyed or 'pruned', with the most-used synaptic connections remaining and the least-used being removed. In other words it seems the brain becomes rapidly over-connected but we only keep the useful connections. This has been thought to be loosely analogous to Darwin's 'survival of the fittest' maxim and hence has been labelled 'neural Darwinism'.
This process allows the formation of significant and long-lasting neural pathways to be influenced by experience early in life.
References
- Edelman, Gerald Neural Darwinism. The Theory of Neuronal Group Selection (Basic Books, New York 1987). ISBN 0-465-04934-6
- Peter S. Eriksson et al. (1998). Neurogenesis in the Adult Human Hippocampus. Nature Medicine (4): 1313-1317.
- Hayek, F. A. The Sensory Order: An Inquiry into the Foundations of Theoretical Psychology xxii, 210 p. 1952 Paper ISBN 0-226-32094-4
- Huttenlocher, P.R. (1990) Morphometric study of human cerebral cortical development. Neuropsychologia, 28, 517-527.
See also
External links
- Citeseer citation index of 'Neural Darwinism' (http://citeseer.nj.nec.com/context/75278/0)
- Citeseer citation index of 'Neural Darwinism', part two (http://citeseer.nj.nec.com/context/283025/0)
- How Brains Think: Evolving Intelligence, Then and Now by William H. Calvin (http://faculty.washington.edu/wcalvin/bk8/)
- Neurogenesis in the Adult Human Hippocampus (http://www.nature.com/neuro/web_specials/supp_info/nm1198_1313/)
- Neurogenesis in the Adult Human Brain (http://www.abacon.com/pinel/hot_sept.html)