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Abstract:
Humans and other non-human animals share a simple design of
two seemingly identical inter-connected cerebral hemispheres.
However, for some functions, one hemisphere dominates, the
processing of language, spatial information, and emotions are quite
lateralized. Neuroanamotical, neurochemical, behavioral, and
pharmacological studies have firmly established that cerebral
lateralization generalizes to non-human species. We test the theory
in rats that functional cerebral lateralization promotes efficient
learning, and that the process of learning further enhances
lateralization. We combined neonatal handling, an early
environmental manipulation, with spatial learning in a water maze
task and operant conditioning of reaching. We found: 1-Neonatal
handling induced a significant left-to-right shift in population
turning bias in the water maze (t=22.780, p<0.001, N=39);
2-Better learners showed stronger right turn preference
(p<0.058, N=19); 3-Left paw preference correlated with one-trial
learning in the water task (t_adj=-2.281 p<0.025, N=38);
4-Learning/practice increased the degree of paw preference in both
handled and non-handled subjects (p<.001). We conclude:
1-Neonatal handling enhances the development of cerebral asymmetry,
specifically inducing right hemisphere dominance in turning but not
reaching. 2-Learning accompanies an increase in the degree of
cerebral lateralization in reaching. 3-Greater right hemisphere
dominance in both turning (R turn) and reaching (L paw preference)
is associated with a greater capacity for spatial episodic memory.
These finding provide suppport for the ``efficient learning''
theory of cerebral asymmetry.
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