Chemical and anatomical plasticity of brain (1964)

Bennett, E. L., Diamond, M. C., Krech, D. et al.

Abstract

The control animals are kept under colony conditions, housed three in a cage and exposed to ongoing activity in the room. ... For enhanced experience, animals were given Environmental Complexity and Training [groups of 10 to 12 animals in large cages provided with toys]. ... For the third condition - reduced experience - animals are caged singly in a dimly lit and quiet room where they cannot see or touch another animal. ... Our observations demonstrate that rats given enriched experience develop, in comparison to restricted littermates, greater weight and thickness of cortical tissue and an increase in total acetylcholinesterase activity of the cortex. ... These changes have been produced consistently in many replications ... they are found in adult as well as young animals. Control experiments have demonstrated that these changes cannot be attributed primarily to differential handling or locomotor activity. ... The demonstration of such changes merely helps to establish the fact that the brain is responsive to environmental pressure.