Development of a cognitive testing apparatus for socially housed mother-peer-reared infant rhesus monkeys

Though cognitive testing of infant monkeys has been practiced for the past 40 years, these assessments have been limited primarily to nursery-reared infants due to the confounds of separating mother-reared infants for assessments. Here, we describe a pilot study in which we developed a cognitive testing apparatus for socially housed, mother-peer-reared rhesus macaques under 1 year of age (Macaca mulatta) that allowed the infants to freely return to their mothers for contact comfort. Infants aged 151.2 ± 18.3 days (mean ± SEM; n = 5) were trained and tested on an object detour reach task. Infants completed training in 5.0 ± 0.2 days, and completed testing in 6.2 ± 0.9 days. Across 4 days of testing, infants improved to nearly errorless performance (Friedman test: χ(2)  = 13.27, df = 3, p = 0.004) and learned to do the task more quickly (Friedman test: χ(2)  = 11.69, df = 3, p = 0.009). These are the first cognitive data in group-housed, mother-peer-reared rhesus monkeys under 1 year of age, and they underscore the utility of this apparatus for studying cognitive development in a normative population of infant monkeys.