Effect of training and environment on brain morphology and behavior.

Using defined rearing or training paradigms, environmental stimulation has been found to increase brain weight (especially forebrain), cortical thickness, the number of glial cells, the glia to neuron ratio, neuronal cell body and nucleus size, and to alter synaptic profiles by increasing dendritic branching, dendritic spine density and the number of discontinuous synapses. Examples will be given from both animal and human studies that document these profound changes. Controversy exists as to whether enriched environments and/or training can compensate for neural deficits produced earlier in life. Examples will be given from animal studies with induced cortical lesions and prenatal genetic neural anomalies that support a role for environmental manipulations ameliorating earlier central nervous system damage.