One group of rats was reared under conditions of environmental complexity, while their littermates served as isolation controls. The occipital cortex was 4.9% (p < 0.01) and the hippocampus 5.7% (P < 0.05) thicker in the environmental complexity rats than in the isolation control animals. Differntial cell counts demonstrated significant differences in neuroglia in the hippocampus.
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Walsh et al. (1969) studied this question.
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