Synapse loss from the rhesus monkey primary visual cortex does not correlate with cognitive decline during aging

Abstract

The effect of age on synapses in the neuropil of layers 2/3 in primary visual cortex was determined in 12 rhesus monkeys of various ages (6-33 years old). All of the monkeys had been behaviorally tested. As determined using the size–frequency method, there is a decrease in the numerical density of symmetric, but not asymmetric, synapses with age. There is no significant correlation between the loss of symmetric synapse frequency and the cognitive impairment indices (CII) of the 12 behaviorally tested monkeys. This lack of correlation between synapse frequency reduction and cognitive decline presumably relates to the fact that the primary visual cortex does not have a direct role in subserving cognition.