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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)
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)
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)
Rapid Golgi preparations from area 17 of young adult rats have been studied to determine the morphology and distribution of non-pyramidal neurons. Such cells were observed in all of the cellular laminae of the cortex, but were particularly prevalent in layers IV and V. Non-pyramidal neurons were categorized according to two features: (1) dendritic(More)
In the rhesus monkey, the myelin sheaths of nerve fibers in area 46 of prefrontal cortex and in splenium of the corpus callosum show age-related alterations in their structure. The alterations are of four basic types. Most common is splitting of the dense line of myelin sheaths to accommodate electron dense cytoplasm derived from the oligodendroglia. Less(More)
The functional significance of dendritic spines and their morphological sensitivity to a wide spectrum of experimental manipulations and pathological states have led to a number of studies in which counts of dendritic spine number have been carried out. These studies have, for the most part, involved the enumeration of only those spines which protrude from(More)
In previous publications we proposed a model of cortical organization in which the pyramidal cells of the cerebral cortex are organized into modules. The modules are centred around the clusters of apical dendrites that originate from the layer 5 pyramidal cells. In monkey striate cortex such modules have an average diameter of 23 microm and the outputs(More)