INTERESTS: Primate, Marmoset, Learning, Prefrontal.
Learning ability in aged marmoset monkeys.
Rodents are not suitable models of human aging processes. Indeed, many drugs developed in rodents do not translate successfully to humans. Nonhuman primate models are ideal because of similar genetic, biochemical, behavioral, and phenotype outcomes. While apes and macaque monkeys have closer evolutionary histories, they are longer lived (> 50 years for apes, and > 30 years for macaques). Shorter lived monkeys, such as common marmosets, can be practical models of human aging. Aged marmosets reportedly exhibit structural changes in skeletal bone, bone loss, loss of weight, and changes in body composition. Several changes in the brain are also reported, including decreased neurogenesis, increased alpha-synuclein aggregation, amyloid-beta deposition, and tau hyperphosphorylation. However, the effects of aging on cognitive functions have not been well-defined. We examined the effects of age on the learning ability in this species using visual pattern discrimination and reversal learning. We compared aged marmosets (10.5 to 14 years old) and 25 young ones (1.7 to 3.5 years old). We found that aged marmosets committed significantly more errors in the visual discrimination learning and more perseverative errors in the reversal learning at the first time, indicating difficulty in learning of new task rules. However, the aged marmosets showed performance comparable to the young on later tasks. Our data suggest mild prefrontal dysfunction in the aged marmosets. In conclusion, the marmoset monkey can be a model of human cognitive aging.