Aging is associated with adverse structural and functional changes in the brain. These changes have been directly linked to declines in certain types of learning and memory, likely due to the negative impact of aging on the hippocampus, a region necessary for cognitive functions such as relational learning, memory, and spatial navigation. Health behaviors and characteristics, like exercise and cardiorespiratory fitness (CRF), are related to better brain and cognitive aging, though more research is needed to better understand which age-sensitive aspects of cognitive function are most benefited by these health characteristics. The purpose of this collection of studies was to examine how exercise and fitness affect older adults’ learning and memory abilities, specifically using tasks that are designed to tax hippocampal binding processes. Further, I aimed to determine whether the volume of the hippocampus plays a key mediating role in this relationship. I answer these questions with three specific aims, each testing part of a model that represents complex interactions between physical activity, fitness, learning, and the potential mediator of hippocampal volume. The first aim examines these relationships using a cross-sectional design of 45 cognitively healthy older adults. The second aim evaluates the effects of a 12-week moderate intensity exercise program on 37 previously low-active older adults’ fitness, hippocampal volume, and relational learning rate. In this aim I first examine the amount of change in multiple variables following the intervention in order to infer causal relations, and then I examine the relationships of change across the different outcome measures. Finally, the third aim evaluates in 40 healthy older adults the role of hippocampal structure in the relationships between fitness and both spatial learning and memory in a virtual navigation task that has been found to be sensitive to age and disease-related changes in the hippocampus.
In the first aim I found that higher cardiorespiratory fitness (CRF) was associated with larger hippocampal volume and faster relational learning rate. Larger hippocampal volume was also associated with faster learning rate. This pattern of results supports my hypotheses and provides a novel finding about how CRF relates specifically to older adults’ relational learning, which is thought to place demands on hippocampal binding.
In the second aim I found that 12-weeks of regular light and moderate exercise increased CRF and early learning of relational associations. These changes were not larger for moderate intensity stationary cycling compared to light intensity stationary cycling. I also unexpectedly found that hippocampal volume decreased for both exercise groups, which suggests that this exercise intervention did not mitigate potential age-related decline in hippocampal volume.
Finally, in the third aim I found that CRF was not related to learning object locations on spatial navigation, but higher CRF was related to fewer memory errors on the delayed recall of object locations in the virtual environment. Additionally, hippocampal volume was positively associated with the number of object locations learned after the first five minutes of free exploration in the virtual environment.
Overall I found that higher CRF is related to faster relational learning and better memory of spatial object locations, both of which are expected to tax hippocampal binding processes. As even healthy older adults tend to experience structural and functional decline in the brain, CRF may be an effective health characteristic to target to increase the active life expectancy of our aging population.