Age-related decline in cognitive flexibility in female chimpanzees.

Data on cognitive aging in chimpanzees are extremely sparse, yet can provide an invaluable phylogenetic perspective, especially because Alzheimer disease (AD)-like neuropathology has recently been described in the oldest chimpanzee brains. This finding underscores the importance of data on cognitive aging in this fellow hominin, our closest biological relative. We tested 30 female chimpanzees, 12-56 years old, on a computerized analog of the Wisconsin Card Sort test. This test assesses cognitive flexibility, which is severely impaired in normal aging and AD. Subjects selected stimuli according to color or shape; the rewarded dimension (i.e., color or shape) switched without warning and the chimpanzee had to adapt her responses accordingly. We found that increasing age was associated with an increased number of perseverative errors and an increased number of trials to reach criterion in each switching dimension. The number of aborted trials was similar across age groups. These data show that similar to humans, chimpanzees show a clear age-related decline in cognitive flexibility that is already observed at middle age.