The secret to a younger brain may lie in exercise, according to a new study.
Published in the journal NeuroImage, the study shows a direct relationship between brain activity, brain function, and physical fitness in a group of older Japanese men.
Researchers at the University of Tsukuba in Japan found that fitter men performed better mentally than less fit men, by using parts of their brains in the same way as younger people.
As we age, we use different parts of our prefrontal cortex, according to the researchers. Located in the very front of the brain, just behind the forehead, the prefrontal cortex has roles in executive function, memory, intelligence, language, and vision.
When we are young, we mainly use the left side of our prefrontal cortex for mental tasks involving short-term memory, understanding the meaning of words, and the ability to recognize previously encountered events, objects, or people. As we get older, we tend to use the equivalent parts of our prefrontal cortex on the right side of the brain for these tasks.
With tasks involving the temporary storage and manipulation of memory-term memories and inhibitory control, young adults favor the right side of the prefrontal cortex, while older adults engage both the right and left prefrontal cortex.
In fact, with aging, we tend to use both sides of the prefrontal cortex during mental tasks, rather than just one, the researchers noted. This phenomenon, which has been coined HAROLD (hemispheric asymmetry reduction in older adults), reflects the reorganization of the brain as it compensates for reduced brain capacity and efficiency due to age-related structural and physiological decline, the researchers explain.
For the new study, researchers had 60 men between the ages of 64 and 75 undergo an exercise test to measure their aerobic fitness.
The men, whose physical fitness varied widely, then performed a test to measure their selective attention, executive function and reaction time. They used the well-known color-word matching Stroop test, in which the men were shown words meaning color, such as blue, green, red, but they were asked to name the color of the letters rather than read the word itself.
This is harder than it sounds, researchers noted. When the color of the letters does not match the word it takes the brain longer to react. This reaction time is used as a measurement of brain function.
Activity in the prefrontal cortex region of the mens’ brains was measured throughout the test using a neuroimaging technique called functional near infrared spectroscopy (fNIRS). This technique provides a measure of blood oxygen concentration in surface blood vessels, which is indicative of activity in the brain’s outer layers.
It does this through a set of wearable probes in a cap that is placed on the head. Active brain cells require fresh oxygenated blood which dislodges the deoxygenated blood from that region. fNIRS measures the changes in color between oxygenated red blood and blue deoxygenated blood, indirectly measuring brain activity.
The researchers then analyzed the results of all the tests to explore the associations between aerobic fitness, Stroop reaction time, and brain activity during the Stroop test.
As predicted for older adults, during the Stroop test both sides of the prefrontal cortex were active, with no difference between right and left, verifying the HAROLD phenomenon in this group of men, the researchers reported. Previous studies have shown that young adults favor the left side of the prefrontal cortex for this task.
Analysis of the relationship between brain activity and Stroop reaction time revealed that the men who favored the left side of the prefrontal cortex 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, according to the researchers.
When the researchers analyzed the association between aerobic fitness and Stroop reaction time, they found that the fitter men had shorter reaction times.
Based on these findings, the researchers correctly predicted that higher aerobic fitness would be associated with higher left-prefrontal cortex activity. In other words, fitter men tend to use the more youth-like side of their brains, at least while performing the Stroop test, they explained.
Using statistical tests called mediation analyses to look at the interaction between the three factors in the study — aerobic fitness, mental performance, and brain activation — the researchers found that aerobically fitter older men can perform better mentally than less fit older men by using the more important brain regions when needed. In fact, the fitter older men are using parts of their brains in the same way as when they were younger, the researchers said. But how?
“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,” said Dr. Hideaki Soya, who led the study. “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.”
Source: University of Tsukuba