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Abstract:
Early experience is critical for the development of the
nervous system and the cognitive functions it subserves. Previous
studies have shown that neonatal handling results in changes in the
hypothalamic-pituitary-adrenal axis, including increased
post-stress corticosterone recovery rate, increased corticosterone
receptor densities, and reduced hippocampal cell death. The
reduction in hippocampal neuronal death was detectable at
approximately 12 months of age and was temporally coupled to a
marked difference in spatial learning in the standard Morris Water
Task (Meaney et al 88). Using a modified handling procedure (split
litter design), a moving platform version of the Morris Water Task
(Whishaw 85), and a one-trial learning measure, we were able to
detect handling-induced enhancement in spatial episodic memory as
early as postnatal week 4 (t=2.050, p<0.025, N=40). This early
enhancement persists (t=1.847, p < 0.05, N=39) and is amplified
into adulthood (P105-110) (t=1.834, p < 0.05, N=39). We
conclude: 1. Neonatal handling enhances the capacity for episodic
memory; 2. Neonatal handling enhances the capacity for rapid
information acquisition from limited exposure, thus we may have an
animal model for "fast mapping" in humans; 3. Neonatal
handling-induced cognitive enhancement can occur very early during
development, and therefore is not limited to the aging process; 4.
Neonatal handling-induced cognitive enhancement persists and
amplifies from early development into adulthood. 5. Mechanisms
other than differential neuronal death must contribute to our
observed cognitive differences during early development.
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