An interesting study here correlates physical fitness to a specific measure of cognitive function and age-related change in brain activity in older individuals. There are numerous mechanisms that might link degree of fitness to the pace of change and neurodegeneration in aging, such as the structural integrity of blood vessels in the brain, which in turn connects to blood pressure, degree to which stiffening occurs in blood vessel walls, and so forth:
A new study shows, for the first time, the direct relationship between brain activity, brain function and physical fitness in a group of older Japanese men. They found that the fitter men performed better mentally than the less fit men, by using parts of their brains in the same way as in their youth. With tasks involving the temporary storage and manipulation of memory, long term memories and inhibitory control, young adults favor the right side of the prefrontal cortex (PFC), while older adults engage both the right and left PFC. In fact, with aging, we tend to use both sides of the PFC during mental tasks, rather than just one. This phenomenon has been coined HAROLD (hemispheric asymmetry reduction in older adults) and reflects the reorganisation of the brain as compensation for reduced brain capacity and efficiency due to age-related structural and physiological decline.
60 older men (aged 64-75 years) underwent an exercise test to measure their aerobic fitness. The men, whose physical fitness was found to vary widely, then performed a test to measure their selective attention, executive function and reaction time. This well-known color-word matching Stroop test involved showing the men words meaning color, such as blue, green, red, but asking them to name the color of the letters rather than read the word itself. When the color of the letters does not match the word - blue, red, green - it takes the brain longer to react. This reaction time is used as a measurement of brain function. Activity in the PFC region of the mens' brains was measured throughout the test.
As predicted for older adults, during the Stroop test both sides of the PFC are active, with no difference between right and left, verifying the HAROLD phenomenon amongst this group of men. Previous studies have shown that young adults favour the left side of the PFC for this task. Analysis of the relationship between brain activity and Stroop reaction time revealed that those men that favored the left side of the PFC while performing the Stroop test had faster reaction times. This indicates that older adults who use the more youth-like, task-related side of the brain perform better in this test. Next, the association between aerobic fitness and Stroop reaction time was analysed. Fitter men had shorter reaction times. Based on these findings, the researchers correctly predicted that higher aerobic fitness would be associated with higher left-PFC activity. In other words, fitter men tend to use the more youth-like side of their brains, at least while performing the Stroop test. "One possible explanation suggested by the research is that the volume and integrity of the white matter in the part of brain that links the two sides declines with age. There is some evidence to support the theory that fitter adults are able to better maintain this white matter than less fit adults, but further study is needed to confirm this theory."