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An analysis has been made of the quantitative data available on the number of pyramidal cell modules of layer IV neurons, and of geniculocortical axons and their synapses in cat striate cortex. It is found that the convergence of geniculocortical afferents upon any one pyramidal cell module is enormous, since in any one location there is overlap between(More)
In monkeys, myelin sheaths of the axons in the vertical bundles of nerve fibers passing through the deeper layers of primary visual cortex show age-related alterations in their structure. These alterations have been examined by comparing the myelin sheaths in young monkeys, 5-10 years old, with those in old monkeys, between 25 and 33 years of age. The(More)
An electron microscopic analysis has been carried out to compare the neuroglial cells and pericytes within the primary visual cortex, area 17, of young (5-6 years) and old (25-35 years) rhesus monkeys. All of the neuroglial cell types accumulate inclusions within their cytoplasm as they age, and the inclusions within the astrocytes and oligodendrocytes are(More)
The effect of age on myelin sheath thickness was determined by an electron microscopic examination of cross sections of the vertical bundles of nerve fibers that pass through primary visual cortex of the rhesus monkey. The tissue was taken from the cortices of young (4-9 years of age) and old (over 24 years of age) monkeys, and the sections were taken at(More)
Using data that are available in various publications, a quantitative analysis has been made of the geniculocortical input to layer IVC of the macaque striate cortex. The data suggest that only 1.3-1.9% of the excitatory, or asymmetric synapses in layer IVC alpha of striate cortex are provided by the neurons of the magnocellular layers of the LGN. This(More)
During normal aging there is a reduction in white matter volume in the cerebral hemispheres and structural abnormalities in myelin in some parts of the central nervous system, but whether nerve fibers are lost with age and whether the myelin changes are ubiquitous is not known. Studying the optic nerve, which is a circumscribed bundle of nerve fibers,(More)
In addition to the horizontal bands of myelinated axons that produce the line of Gennari and the inner band of Baillarger, the macaque primary visual cortex contains prominent vertical bundles of myelinated axons. In tangential sections through layer IVC, these axon bundles are regularly arranged. They have a mean center-to-center spacing of about 23(More)
The rhesus monkey offers a useful model of normal human aging because when monkeys are tested on a battery of behavioral tasks that can also be used to evaluate cognition in humans, it is found that the monkeys undergo an age-related decline in several domains of cognitive function as do humans. In monkeys these changes begin at about 20 years of age. To(More)
An examination of cortex of area 46 in the floor of the principal sulcus in the frontal lobe of the rhesus monkey has been carried out using three young (4-6 years of age), one middle-aged (12 years of age), and five old (25-32 years of age) rhesus monkeys. Light microscopic examination revealed no age-related change in the thickness of the cortex, and no(More)