ONTOGENY OF GOAL-DIRECTED BEHAVIOR - ANATOMO-FUNCTIONAL CONSIDERATIONS

Recent neuroanatomical and neurophysiological studies in man have reve aled ontogenetic events which coincide with broadly defined phases of behavioral and cognitive development. During the early fetal period, e arly produced neurons make initial synapses which form the basis for t he earliest electrical activity of the human brain. The overall immatu rity of neuronal connections, in particularly in cortical areas, corre lates with the absence of any behavioral pattern or goal-directed move ments. In the late fetus and preterm infant, transient accumulation of major afferent pathways, the presence of transient layers (subplate z one) and transient pattern of transmitter-related organization form th e neurological basis of cortical electric responses as well as transie nt behavioral states and sleep patterns. Parallel to the profound stru ctural and chemical reorganization of the human cerebrum during the fi rst 6 postnatal months there is a disappearance of transient behaviora l and motor patterns. The previously close spatio-temporal correlation between these events becomes progressively looser. The overproduction of circuitry elements during the subsequent period peaks in associati ve cortex between 1 and 2 years of age, corresponding to the emergence of skilled actions and cognitive functions. After the elimination of some circuitry elements after the second year of life, the prolonged m aturation of goal-directed behavior and the protracted emergence of di fferent cognitive functions correlates with the developmental plateau of synapse production which can be seen up to 16 years of age. Paralle l to the prolonged maturation of postsynaptic elements, there are well defined maturational changes in the chemical properties of associativ e pyramidal neurons of cortical layer III. These findings correspond t o the prolonged maturation of movement-related brain macropotentials a s well as other cognition-related potentials, where, the last prominen t changes were seen after 10 years of age. Although the coincidence of the developmental events does not necessarily mean a causal relations hip, the combination of structural and physiological data opens new vi stas for the further investigation of the neurobiological basis of goa l-directed movement and cognitive behavior.