Effects of early environments on monkey cortex neuroanatomical changes following somatomotor experience: effects on...

Sixteen infant stumptail monkeys were reared to 6 months under four conditions. Behaviors and cortical neuroanatomy were compared. Earlier studies showed effects on stellate cell dendrites. Here are reported the results in six cortical areas on basilar dendrites of layer III pyramidal cells. Basilar dendrites show significantly larger numbers (p less than .05) of branching for motor I cortex under condition 3 associated with the greatest skills and amount of activity in climbing, swinging, and grasping of objects. Visual cortex was not significantly altered by the rearing conditions, but the basilar dendrites showed less branching than in the five other areas of cortex sampled. It is concluded that genetic factors are responsible for the major growth patterns and that environmental factors contribute to quantitative increases or decreases in the branching of dendrites and therefore the finer tuning of neural interconnections.