to sufficient demand ( Black et al., 1990). The implication of these results is that, although the brain remains quite capable of adding synapses at this age, providing metabolic support for the massive numbers that are added as a result of exposure of individually reared animals to a complex environment at this age is no longer possible. The result could be what Smith ( 1984) termed a power failure under conditions of sufficiently great transient demand.
A great deal of detail remains to be filled in with regard to metabolic support, but one aspect seems clear: whereas the capacity to generate new synapses is not limited to early periods of development, there are critical periods for, or at least periods of differential ability of, the brain to provide other supporting aspects. To the extent that additional synapses represent either additional memory or additional capacities (alternatives not mutually exclusive), access to them might be more limited in the case of later acquisition, if the brain had not received the appropriate early experience.
Preparation of this chapter and research not otherwise reported was supported by NIMH 35321 and 40631, NIH RR 07030, PHS 5 T-32EY07005, PHS 5 T-32GM7143, ONR N00014-85-K-0587, the Retirement Research Foundation, the System Development Foundation, and the University of Illinois Research Board.
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