Aging affects executive functions and memory in mouse lemur primates

The decline of cognitive capacities with age in mouse lemur primates (Microcebus murinus) was assessed. Eight young adults (2-4 years) and nine aged adults (7-11 years) were examined on tasks designed to measure executive functions, procedural and declarative memory. The mouse lemurs were tested on the go-no go successive discrimination task, set shifting tasks (including extra-dimensional shift and reversal discrimination) and a spatial rule-guided discrimination task. There were four major findings. First, the deficits observed were not global but only on specific tasks indicating that only specific cognitive abilities are impaired with aging. Second, there were variations among aged subjects suggesting different patterns of cognitive aging. Third, alterations in cognitive abilities with aging in mouse lemurs seemed to be comparable to those described in aged monkeys and humans. Indeed, executive functions and declarative memory were affected in subpopulations of aged subjects whereas procedural memory remained intact in all the tested aged subjects. Finally, two forms of executive dysfunctions were distinguished among the aged subjects. The ultimate goal is to correlate age-related cognitive deficit with brain alterations and this study has helped to select candidate regions to be thoroughly scrutinized in aged mouse lemurs.