Background
We have found that aged dogs develop a range of cognitive impairments. They become deficient in learning (acquiring new information); in maintaining information in short-term memory; and in storing information in long-term memory for later use.
The saying, however, is still not completely accurate.Like people, some old dogs can be classified as successful agers and are virtually indistinguishable from young dogs with respect to most indices of cognitive function. A second group of old dogs can be identified which show relatively mild impairment, but are clearly distinct from young dogs. Yet another group of old dogs show severe generalized impairment, bordering on dementia.
Impaired cognition is not the only effect of age; the structure of the central nervous system changes as well. These age-related changes are indicated by loss and shrinkage of nerve cells, expansion of the brain ventricles - fluid filled cavities- and in the development of various pathologies. The most notable such pathology is the accumulation of beta-amyloid plaques.