Date Published: April 24, 2019
Publisher: Public Library of Science
Author(s): Regina Paxton Gazes, Meredith C. Lutz, Mark J. Meyer, Thomas C. Hassett, Robert R. Hampton, Elsa Addessi.
Animals housed in naturalistic social groups with access to automated cognitive testing vary in whether and how much they participate in cognitive testing. Understanding how demographic, seasonal, and social factors relate to participation is essential to evaluating the usefulness of these systems for studying cognition and in assessing the data produced. We evaluated how sex, age, reproductive experience, seasonality, and rank related to patterns of participation in a naturalistic group of rhesus monkeys over a 4-year period. Females interacted with the touchscreen systems more than males and were more likely to complete initial training. Age was positively correlated with touchscreen activity through adolescence in females, at which point seasonality and reproductive experience were stronger associates of participation. While monkeys in different rank categories did not differ in how much they interacted with the touchscreen systems, monkeys of different ranks tended not to work at the same times, perhaps reflecting avoidance of high ranking animals by those of lower rank. Automated cognitive testing systems for naturalistic social groups of rhesus monkeys can yield quality cognitive data from individuals of all ages and ranks, but participation biases may make it difficult to study sex differences or seasonal variation in cognition.
Decades of carefully controlled research with animals housed singly or in small groups has produced an essential base of knowledge on the mechanisms underlying cognition [1, 2]. In many nonhuman primate species, cognitive processes such as learning and memory evolved and function in complex social contexts. Recently there has been increased interest in understanding how these cognitive processes function in social settings and how social factors relate to cognitive function [3, 4]. Testing cognition in naturalistic social groups allows researchers to pose a broad array of research questions not possible in traditional research settings, including whether there is a relationship between dominance rank and cognitive processes , what animals know about their social relationships , and whether cognition relates to reproductive success .
All procedures were approved by the Institutional Animal Care and Use Committee of Emory University (Protocol numbers YER-2001135-090212GA and YER-2002015-081515GA) and complied with the National Institutes of Health guidelines for the care and use of laboratory animals.
While the first study focused on how demographic factors relate to whether a monkey interacted with the touchscreen system, and thus whether they completed the short initial training, other factors may be related to how much, when, and with whom individual monkeys interact with the system. Monkeys who completed training were presented with a variety of cognitive tasks to complete at their own pace, and as there were four adjacent testing systems, multiple monkeys could participate in cognitive testing at the same time. We determined the extent to which sex, age at training, age at testing, reproductive experience, and social rank related to 1) amount of touchscreen activity, 2) daily trends in touchscreen use, and 3) which pairs of monkeys worked concurrently on the touchscreen systems.
Overall, about half of the monkeys present during the study completed initial training, qualifying them to participate in cognitive testing. Females were more likely to complete training than were males and interacted more with the touchscreen systems after initial training. Monkeys that were younger when they received access to the testing system were more likely to complete initial training. In females, age was positively related to touchscreen activity through adolescence, at which point seasonality and reproductive experience were stronger predictors of monthly touchscreen activity. This suggests that engagement with the touchscreen systems decreased when animals had additional demands on their activity budgets from mating, birthing, and infant care. Monkeys in different rank categories did not differ in how likely they were to interact with the touchscreen systems. However, low ranking monkeys appeared to time their use of the systems to minimize conflict by using the systems when they were not in use or were in use only by other low ranking monkeys.