Development and plasticity of the primate cerebral cortex.

The results of our studies of corticocortical connectivity in developing monkey association cortex contrast with those obtained in similar studies of sensory regions in other species. In association areas of the monkey, these connections emerge very early in development, and many of the details of their organization are well specified from their earliest appearance. The presence of an adultlike pattern of organization a full month before birth suggests that these events probably are determined in large part by forces independent of general environmental stimulation, unlike the pattern seen for sensory regions in the cat. Do these differences reflect variations between species or between the development of sensory and nonsensory regions of the cortex? The answer is probably both. Our results suggest that diverse areas of the brain may differ in the extent to which they respond to environmental influences. For example, many of the organizational features that apparently emerge from an initially diffuse organization in sensory areas appear to be more strictly specified in their initial formation in the prefrontal cortex. However, we should not rule out the possibility that many of the features of connectional organization that are responsive to the environment in the sensory areas (e.g., the distribution of corticocortical neurons) develop in the prefrontal cortex during the prenatal period and therefore may simply be buffered from the effects of environmental stimuli. In addition, many aspects of the circuitry of the prefrontal cortex clearly continue to develop well into the postnatal period and may be subject to modification by experience. Among these are the organization and density of synaptic contacts and the elaboration of dendritic surfaces. Although relatively little is known concerning the response of these features to stimulation in the prefrontal cortex, studies from sensory areas suggest that these may be good candidates for modification by external interventions. The text of this paper was taken from a presentation given at the 1986 Johnson and Johnson Pediatric Roundtable. In the period between the original talk and the publication of this article, several studies have emerged on the development of corticocortical connectivity in sensory cortical regions of nonhuman primates. In agreement with our data in the monkey prefrontal cortex, these studies have also found that the distribution of callosal neurons in the somatosensory and visual cortices is adultlike at least 1 month prior to birth.(ABSTRACT TRUNCATED AT 400 WORDS)