The behavioral effects of age-related brain changes
Before we can assess behavioral effects of brain aging, it's helpful to have some estimate of the range of cat behaviors over
time in a controlled situation.
A study published in 1987 that focused on groups of research colony cats aged 1 to 3, 5 to 9 and 11 to 16 years assessed locomotor
activity, plank walking, reactivity and spatial-reversal learning.7 This study produced some surprising findings. Cats in the oldest group were relatively insensitive to habituation in locomotor
sessions, but younger cats habituated quickly. As a result, older cats did not change activity between or within sessions
to the extent that younger cats did. Younger cats seemed to decide if the task wasn't novel, it wasn't worth doing. This may
mean older cats have an altered sensitivity to environmental stimuli, but they also made fewer mistakes in walking planks
than did the youngest cats and showed no differences in neurobiological assessment when compared with the other two age groups.
These findings may impact how we should assess older cats. Because older cats are willing and able to perform certain tasks
repeatedly, it does not mean that ongoing aging of the brain is not taking place. Other similar findings of this research
were also interesting in this regard.
For example, older cats were more reactive to auditory stimuli than were younger cats, and they sustained their responses
longer. The oldest cats (aged 11 to 16 years) actually performed better on a spatial-reversal learning task than did their
younger counterparts. Older cats made fewer errors and learned to reverse faster, although they did not appear to maintain
learning between tasks. The oldest cats seemed to have some short-term memory deficits but appeared to view each trial of
the specific task as a new learning experience, as determined by a test for randomness in their first few sets of responses
(the cats in the two younger groups did not show this randomness in response). Furthermore, these older cats learned from
their incorrect responses.
Note that all of the cats tested came from breeding colonies, so they may have had more complex cognitive and experiential
lives than do most people's pets. If that's true, it should give us pause. This experimental report may suggest that problem-solving
activity early and throughout life would benefit pet cats.
Clinical reports based on client interviews have suggested that 29 percent of pet cats 11 to 14 years old express at least
one geriatric-onset behavior problem, and that by 15 years of age, this is true for 50 percent of pet cats.8 Assessment of behavioral change in any species is not trivial because behavior is the integrating component that reflects
the whole of any animal. In older cats, the most commonly reported behavioral changes include alteration in social interactions
with humans or other animals, overall activity (including changes in quality of activity from that which was previously directed
to that which is now aimless), sleep-wake cycles, grooming, feeding and interest in food, learning and generalized behavioral
responses and increases in amount and changes in quality of vocalization.
Owners recognize many veterinary problems in their pets because of a change in behavior at some level, and classes of behavioral
change can be both nonspecific signs and specific indicators of underlying neurocognitive change. Teasing apart these two
can be challenging, especially in a cat that we may not have watched closely and that may remain more of a mystery to the
average human than the comparatively transparent dog.
There are few standardized behavioral tests of cognitive function for either pet dogs or cats. However, some of the behavioral
tests designed in the 1990s9 to assess cognitive function in cats affected by feline immunodeficiency virus (FIV) infection may have some promise for
laboratory studies of aging cats and, better yet, may be sufficiently portable to make at-home or in-hospital testing possible.
Factors that may confound our interpretation of such tests and client histories may include the presence of arthritis (which
can impede movement), pain from any source, endocrine disease (including hyperthyroidism), renal or hepatic disease and failure,
primary neurologic disease, gingival disease (some behavioral tests require the apprehension of food), blindness, deafness
or infectious conditions (e.g., FIV) that affect nervous tissue.