Normal and aberrant neuronal development in the cerebral cortex of human fetus and young infant.

Several approaches utilized in ontogenetic investigations in laboratory animals have been explored in preliminary studies of morphogenetic events in the human cerebral cortex. 1. Golgi studies of dendritic growth cones, filopodia, and other developmental processes have permitted specification of the maximal phase of dendritic growth and differentiation of pyramidal neurons in the hippocampus. This period spans the twentieth to twenty-eighth week of fetal development. 2. Studies of the temporal pattern of appearance of the axonal plexus of the stratum pyramidale suggest that axosomatic synaptic pathways in the hippocampus develop relatively late in respect to the appearance of axospinodendritic inputs. 3. Dendritic spine development is evident at 26 weeks g.a. in the hippocampus but not in the visual cortex. Most hippocampal pyramidal neurons have acquired a full complement of spines by 6 months postnatally. The presence of severe metabolic and cardiorespiratory disturbances and/or chromosomal abnormalities significantly influences dendritic spine morphology and development. 4. The general morphological features of several varieties of neurons in the cisual cortes of a 32-week-old preterm infant are considered in respect to the electrographic characteristics of this infant's visual evoked responses. The observations in this and other cases illustrate the manner in which ontogenetic problems susceptible to inquiry in laboratory animals can serve to guide similar morphophysiological studies of normal and aberrant developmental events in human brain.