Age-related motor dysfunction: Manual slowing in Gorilla gorilla gorilla.

Aging in humans and rhesus monkeys is commonly associated with motor function decrements including dexterity, speed, and strength. Despite their longevity and phylogenetic relatedness to humans, the effects of aging on motor function in non-human apes have been minimally studied. We conducted two experiments with western lowland gorillas (11-54 years of age) to determine whether aged gorillas exhibit motor deficits similar to those seen in other species. In experiment one, gorillas extracted up to 12 food rewards lodged in holes of a Lexan board. Extraction rates were calculated for eight test sessions. A repeated measures ANOVA revealed no main effects of session or sex on extraction rate, but a significant main effect of age. Comparisons between the first and last sessions showed that experience significantly improved extraction rates in young but not aged gorillas. In experiment two, gorillas retrieved a hex nut from three differently shaped rods with each hand for a reward. Latencies of retrieval were calculated for 16 test sessions. A repeated measures ANOVA revealed significant main effects of age class, sex, and session. There were significant interactions between session and sex, session and age, and session, sex, and age. These findings held when analyzing each rod shape separately. Post hoc comparisons revealed that young gorillas were significantly faster at the task than aged gorillas, and females were faster than males. This finding held only for the question mark shaped rod when analyzing each rod shape separately. Comparisons between the first and last sessions showed that experience did not significantly improve latencies in either age or sex class. The direction of these results are congruent with previous findings in humans and monkeys and suggest that aged gorillas experience deficits in bimanual coordination compared to younger gorillas and that age and sex influence fine motor ability in gorillas.