Journal of Neuroscience, Vol 4, 25-42, Copyright © 1984 by Society for Neuroscience
Development of prestriate visual projections in the monkey and human fetal cerebrum revealed by transient cholinesterase staining
I Kostovic and P Rakic
Cholinesterase (ChE) staining was used to reveal the timing and pattern of
development of afferents to the prestriate visual cortex (areas 18, 19, 20,
and 21 of Brodmann) in a series of developing human and monkey fetal
brains. This investigation was possible because the nucleus pulvinaris of
the thalamus, the main source of subcortical projections to the prestriate
cortex, displays positive reactivity after thiocholine incubation during
the last three quarters of gestation, while neighboring thalamic nuclei
that project to the adjacent neocortical areas are unstained. Staining of
the pulvinar and its prestriate projections passes through six broad
stages. Stage I begins in both species at the end of the first third of
gestation. Positively stained fibers originate from the pulvinar and enter
but do not extend beyond the hemispheric stalk. During stage II, pulvinar
axons gradually invade the intermediate zone of the occipital lobe, and in
stage III they reach the level of the subplate zone. In stage IV, which
occurs around mid-gestation in both species, cholinesterase-positive fibers
accumulate within the subplate zone subjacent to the developing prestriate
cortex. During stage V, ChE-positive fibers penetrate the prospective
prestriate cortex but do not yet form the alternating columnar pattern
characteristic of pulvinar input to this area in the adults. Rather, ChE
activity is concentrated in two continuous bands situated within
prospective layers III-IV and VI; also a narrow band is visible in upper
layer I. In stage V a clear histochemical border forms between prestriate
and striate areas with ChE activity in prospective area 17 limited mostly
to the superficial strata of layers I and II. This histochemical
differentiation precedes the emergence of cytoarchitectonic landmarks.
During stage VI, which begins in the last fifth of gestation in both
species, the pulvinar become progressively less stainable and its
projections can no longer be traced by ChE histochemistry.
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