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Journal of Neurocytology 31, 373–385 (2002)

Frontal lobe and cognitive development
Neuropsychiatric Institute and Brain Research Institute, UCLA School of Medicine Los Angeles, California Received December 1, 2002; accepted December 12, 2002

In phylogeny as in ontogeny, the association cortex of the frontal lobe, also known as the prefrontalcortex, is a late-developing region of the neocortex. It is also one of the cortical regions to undergo the greatest expansion in the course of both evolution and individual maturation. In the human adult, the prefrontal cortex constitutes as much as nearly one-third of the totality of the neocortex. The protracted, relatively large, development of the prefrontal cortex is manifest in grossmorphology as well as fine structure. In the developing individual, its late maturation is made most apparent by the late myelination of its axonal connections. This and other indices of morphological development of the prefrontal cortex correlate with the development of cognitive functions that neuropsychological studies in animals and humans have ascribed to this cortex. In broad outline, theventromedial areas of the prefrontal cortex, which with respect to other prefrontal areas develop relatively early, are involved in the expression and control of emotional and instinctual behaviors. On the other hand, the late maturing areas of the lateral prefrontal convexity are principally involved in higher executive functions. The most general executive function of the lateral prefrontal cortex isthe temporal organization of goal-directed actions in the domains of behavior, cognition, and language. In all three domains, that global function is supported by a fundamental role of the lateral prefrontal cortex in temporal integration, that is, the integration of temporally discontinuous percepts and neural inputs into coherent structures of action. Temporal integration is in turn served by atleast three cognitive functions of somewhat different prefrontal topography: working memory, preparatory set, and inhibitory control. These functions engage the prefrontal cortex in interactive cooperation with other neocortical regions. The development of language epitomizes the development of temporal integrative cognitive functions and their underlying neural substrate, notably the lateralprefrontal cortex and other late-developing cortical regions.

Introduction The prefrontal cortex is the cortex of association of the frontal lobe. In the mammalian brain, this cortex is conventionally defined by two basic criteria: cytoarchitecture and connectivity. Both criteria serve us to delimit approximately the same cortical territory, which is characterized in all mammalian species by aprominent cellular layer IV, or granular layer, and a tight reciprocal connectivity with the mediodorsal nucleus of the thalamus. In the primate, human or nonhuman, the prefrontal cortex has three major anatomical aspects or regions: lateral, medial, and ventral or orbital (Fig. 1). Each prefrontal region is subdivided into areas of varying cytoarchitecture, providing the grounds for a number ofcytoatchitectonic maps, such as that of Brodmann (1909). With few exceptions, such as that of area 8, which is largely devoted to the control of gaze and eye movements, it is not possible to ascribe a specific physiological function to any prefrontal area. However, it seems obvious that the prefrontal cortex is functionally heterogeneous. Whereas it cannot be functionally parceled out with regard toits cytoarchitecture, there is substantial evidence that, as a whole, the prefrontal cortex per0300–4864

forms a critical role in the organization of behavioral, linguistic, and cognitive actions. The psychological and physiological analysis of this role in the three action domains yields a topographic distribution of cognitive functions conforming to the following outline. All three...
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