Effect of age and level of cognitive function on spontaneous and exploratory behaviors in the beagle dog

Abstract

Cognitively characterized young and aged beagle dogs were administered six different spontaneous behavior tests, which provided measures of locomotion, exploration, and social interaction. Consistent with our previous findings, we obtained no overall effect of age on locomotion. We did find, however, that for the aged dogs locomotion correlated with level of cognitive function, being lowest in age-unimpaired dogs and highest in impaired dogs. Exploratory behavior, as measured by response to novelty, varied with age, with young dogs scoring the highest. Young dogs spent more time with novel toys and a person, responded more to a silhouette of a dog, and interacted more with a model dog compared to aged dogs. Among the aged dogs, age-unimpaired dogs spent the greatest amount of time sitting or standing beside a person whereas age-impaired dogs spent the most time reacting to a reflection in a mirror. The age-impaired dogs show undirected, stereotypical types of behavioral patterns. These differences in activity patterns may be linked to underlying age-associated neuropathology.

Figure 1

The combined sum of errors required to learn a delayed nonmatching to position task and a size discrimination learning task are plotted as a function of age and presence or absence of cognitive impairment.

Figure 2

Locomotion in an open field for young, age-unimpaired and age-impaired groups. There is no difference between young and aged dogs in locomotion unless cognitive status is taken into account. The age-unimpaired dogs showed lower levels of locomotion than the young (P = 0.058) and age-impaired (P = 0.067) groups. Error bars represent standard errors of the mean.

Figure 3

Time in seconds that dogs spent interacting with their reflection in the mirror. Age-impaired dogs spent significantly more time interacting with a mirror reflection than age-unimpaired (P = 0.018) dogs. The young dogs were intermediate between the two age groups. “a” is significantly different from “b”. Error bars represent standard errors of the mean.

Figure 4

Time in seconds that the dogs spent sitting or standing beside the person in the human interaction test. The age-unimpaired dogs spent significantly more time close to the person than the age-impaired (P = 0.009) and young dogs (P = 0.015). “a” is significantly different from “b”. Error bars represent standard errors of the mean.

Figure 5

Tracings of the movement patterns of the dogs in the test room. The activity patterns of the age-impaired dogs did not change with the different tests. This group showed the same pattern regardless of stimuli present. The young and age-unimpaired dogs modified their behavior according to the test situation. MR, mirror test; HI, human interaction test; CU, curiosity test.