Corticocortical pyramidal neurons have short apical dendrites which never reach higher than layers 2/3, small to medium sized cell bodies and a few basal dendrites. The first one refers to corticocortical pyramidal neurons. Two main classes of pyramidal neurons have been described in layer 5, each of them playing a unique role in visual information processing. In order to further examine the possible age-related alterations in the human visual cortex, we focused on the pyramidal cells of layer 5 of the human visual cortex. (2007) in a Golgi study in rats, revealed age-related changes in dendritic branching and spinal density of the pyramidal cells of the visual cortex. However, electron microscopy revealed fewer dendritic and spine profiles per unit area, thickening of the glia limiting membrane and a concomitant decrease in the numerical density of synapses with age. (1990), who concluded that there is no significant loss of neurons during ageing.Īccording to light microscopy, no significant changes in length and complexity of the dendritic arbor were found to correlate with age-related functional alterations in layer I of rhesus monkeys. (1989), Peters and Sethares (1993) and Tiggers et al. The latter findings are in agreement with studies of Vincent et al. Brody (1955) and Samorajski (1976) in their early studies mentioned a significant neuronal loss during normal ageing, whereas Pakkenberg and Gundersen (1997) in a more recent study suggested a small loss of neurons with age. Īlthough a decrease in brain size has been reported with increasing age, there is some evidence that gray matter tissue loss is minimal in patients without degenerative abnormalities. (2006) described significant functional degradation of the primary visual cortex in aged animals, which could be regarded as direct evidence for the loss of function in visual cortical cells. Several conflicting lines of evidence exist so far concerning the possible causative mechanism for such impairment. Anatomical and morphological studies concluded that retinal abnormalities and changes of the subcortical areas do not efficiently explain the perceptual deficits, and recent neuroimaging studies suggest that age-related dedifferentiation may apply at a neural level besides photoreceptors. Normal aging is characterized by deterioration of visual abilities, affecting mainly visual acuity, contrast and wavelength sensitivity.

Varicose dendrite definition