[Morphological development of the primary visual pathway in the child].

This study concerns the development of the human primary visual pathway. The lateral geniculate nucleus (LGN), the principle thalamic relay to the visual cortex (area 17), has a population of neurons similar to that of the monkey, as identified by Golgi impregnation. Commonest neuron is the multipolar with a radiate or tufted dendritic tree, followed by the bipolar neuron with two or three diametrically opposed dendritic trunks and, more rarely, neurons with beaded dendrites and those with fine, axon-like dendritic processes, possibly interneurons. The dendritic tree of all neurons remains generally within a lamina, but some dendrites cross interlaminar zones. These zones contain neurons whose dendrites enter adjacent laminae. LGN neurons are identifiable at birth, and even earlier, and differ from their adult form by the presence of immature features (growth cones and numerous dendritic and somatic spines), most frequent at four months but disappearing completely by nine months post-natally, when the LGN has reached its "adult" volume. Two stages in the development of area 17 can be defined. The first is marked by rapid growth to its "adult" volume at about four months, and by intense synaptogenesis beginning in the foetus and reaching a maximum around eight months. The second stage is one of stabilization of volume of area 17 and loss of synapses to reach "adult" synaptic density around 11 years, at about 60 p. cent of maximum values. The formation of transitory morphological features in the first year coincides with a period of visual plasticity in the infant. Our observations can be correlated with clinical evaluations of visual activity during the preverbal stage, a period of great importance in the establishment of visual acuity, of stereopsis, and of oculomotor function, all very sensitive to the numerous forms of visual deprivation.