Figure 4.

Increase in brain size and the maturation of cortical circuits. The maturation of mental processes and motor skills is associated with an approximately fourfold enlargement in brain size. (A,B) photographs of the brains of a 1-month and 6-year-old-child. This increment is accompanied by a dramatic development in the complexity of the neuronal processes, which in turn is influenced by the genetic background and the environment. This increase in the complexity is clearly evident in the drawings of Golgi stained cortical neurons from the cerebral cortex of a 1-month [(C) “pars triangularis of gyrus frontalis inferior”; (D) “orbital gyrus”] and 6 year [(E), “pars triangularis of gyrus frontalis inferior”; (F) “orbital gyrus”] old child. Adapted from Conel and Le (1941, 1967). Scale bar for (A,B): 2 cm.