Abstract
Mouse lemurs are suggested to represent promising novel non-human primate models for aging research. However, standardized and cross-taxa cognitive testing methods are still lacking. Touchscreen-based testing procedures have proven high stimulus control and reliability in humans and rodents. The aim of this study was to adapt these procedures to mouse lemurs, thereby exploring the effect of age. We measured appetitive learning and cognitive flexibility of two age groups by applying pairwise visual discrimination (PD) and reversal learning (PDR) tasks. On average, mouse lemurs needed 24 days of training before starting with the PD task. Individual performances in PD and PDR tasks correlate significantly, suggesting that individual learning performance is unrelated to the respective task. Compared to the young, aged mouse lemurs showed impairments in both PD and PDR tasks. They needed significantly more trials to reach the task criteria. A much higher inter-individual variation in old than in young adults was revealed. Furthermore, in the PDR task, we found a significantly higher perseverance in aged compared to young adults, indicating an age-related deficit in cognitive flexibility. This study presents the first touchscreen-based data on the cognitive skills and age-related dysfunction in mouse lemurs and provides a unique basis to study mechanisms of inter-individual variation. It furthermore opens exciting perspectives for comparative approaches in aging, personality, and evolutionary research.
Highlights
In humans there is strong evidence for inter-individual variability in the decline of cognitive ability with age
Our findings revealed for the first time that young and aged mouse lemurs could be successfully trained on a visual pair-wise discrimination task and its reversal using a touchscreen standardized automated system
We found age-associated cognitive decline in the acquisition of the visual discrimination as well as in the reversal learning
Summary
In humans there is strong evidence for inter-individual variability in the decline of cognitive ability with age. The life expectancy of mouse lemurs is higher in captivity: for our colony, the maximum recorded lifespan is 15 years. Due to their mouse-like body size, the maintenance and breeding of mouse lemurs is cost-efficient [11]. Dhenain and colleagues later demonstrated iron accumulations in the mouse lemur brain as a process of non-pathological aging but with the same topography as in humans [21]. A recent study demonstrated that mouse lemurs seem to be the only non-human primates reproducing the link between regional cerebral atrophy and ageassociated cognitive alterations [23]. Developing sensitive, reliable, and translational tasks to assess specific cognitive domains is, crucial to understand underlying neural mechanisms during aging
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