Early postnatal development of the monkey visual system. I. Growth of the lateral geniculate nucleus and striate cortex.

The postnatal growth of the dorsal lateral geniculate nucleus (LGNd) and the striate cortex (SCx) was compared in the same monkeys, by estimating LGNd volume, and the volume, surface area, and thickness of the SCx at birth, 1, 2, 4, 8 and 17 weeks. Shrinkage during histologic manipulations was determined in individual animals, and the above measurements were adjusted accordingly so that final volumes reflected a common, and, therefore, comparable state before processing. The volume of the LGNd increases approximately 17% between 2 and 4 weeks, and this growth primarily reflects that of the parvocellular laminae, the magnocellular components contributing a stable amount in absolute terms. Lamina 1 is larger than lamina 2 at all ages sampled. In contrast, the SCx expands about 75% in volume from birth to the oldest age examined without reaching an asymptote during the period of study. During the first 2 postnatal months, the growth results from increases in the thickness of the SCx whereas in the second 2 months it is caused by expansion in surface area. A comparison of exposed vs buried SCx does not reveal differences in the developmental patterns of regions subserving central vs peripheral visual fields, respectively, the exposed cortex being consistently greater in volume and area but thinner than the buried segment. No significant right/left asymmetries are found across the subjects in either of the structures studied. The findings indicate that the early postnatal development of the monkey visual system proceeds in a sequential fashion with the LGNd preceding that of the SCx.