Qualitative and quantitative development of the visual cortex in man

Anatomical parameters derived from an analysis of 35 male brains, ranging in age from 137 days after conception (DAC) to 99 years, were studied in reference to the development of the human visual cortex (area 17). Distinct structuring of laminae V and VI of area 17 is present at 137 DAC, contrasting with the relative undifferentiation of area 18 at this time. Both the differentiation of the visual cortex into the fundamental six laminae of Brodmann and the emergence of the stripe of Gennari occur between 180 and 190 DAC. At this time, sublamina IVa emerges as a separate entity, external to a transient, trilaminated cortical complex of which the two internal components form sublamina IVc while the external component becomes a part of sublamina IVb (stripe of Gennari). Lamination in area 18 follows a different time course than area 17, appearing at about 160 DAC and achieving a definite six‐layered structure at the 185th DAC. The widths of the laminae in both areas continue to fluctuate after the 190th DAC while the cellular density appears to decrease. The fresh volume of the visual cortex was determined from stained serial sections of the brain, following adjustment for artifactual shrinkage. Approximations of values utilizing the 3‐, 4‐, and 5‐parametric logistic functions reveal that maximum growth of this area occurs at birth, with area 17 attaining 50% of its maximum volume. The maximum volume is reached at the 300th DAC and it apparently begins to decrease in the first decade. The visual cortex develops at a considerably faster rate and reaches its maximal volume much earlier than does the whole brain, cerebellum, or hippocampal formation.