Postnatal development of intrinsic horizontal axons in macaque inferior temporal and primary visual cortices

Abstract

Two distinct areas along the ventral visual stream of monkeys, the primary visual (V1) and inferior temporal (TE) cortices, exhibit different projection patterns of intrinsic horizontal axons with patchy terminal fields in adult animals. The differences between the patchesin these 2 areas may reflect differencesin cortical representation and processing ofvisual information. We studied the postnatal development of patches by injecting an anterograde tracer in to TE and V1 in monkeys of various ages. At 1 week of age, labeled patches with distribution patterns reminiscent of those in adults were already present in both areas. The labeling intensity of patches decayed exponentially with projection distance in monkeys of all ages in both areas, but this trend was far less evident in TE. The number and extent ofpatches gradually decreased with age in V1, but not in TE. InV1, axonal and bouton densities increased postnatally only in patches with short projection distances, whereas in TE this density change occurredinpatches with various projection distances. Thus, patches with area-specific distribution patterns are formed early in life, and area-specific postnatal developmental processes shape the connectivity of patches into adulthood.