Why Does Reaction Time Decrease With Age?

Aging causes a loss of brain connections and slows reaction time, reports a University of Michigan study. However, other studies show that exercise reverses and maintains youthful reaction times.

The corpus callosum bridges or stops communication between the two brain hemispheres. The bridge action is vital to performing two-sided motor skills and certain cognitive functions. However, during one-sided motor movements, the corpus callosum needs to block off the other brain half that controls the opposite side of the body. As a person ages, there is an increased tendency for both brain halves to talk at once, which slows reaction time.

In diseases such as multiple sclerosis, the corpus callosum is deteriorated to the point where both sides of the body move during one-sided motor tasks because both brain hemispheres communicate simultaneously. Very young children have an undeveloped corpus callosum and move in a similar way. In response to these findings, researchers are developing and piloting motor training studies aimed at limiting the overflow between hemispheres.

Other studies have shown that exercise helps maintain youthful reaction times. The University of Michigan study only compares people in their 20s to people in their 70s. Reaction times between a 20- to 25-year-old age group and a 45- to 55-year-old age group of physically fit men show only a negligible difference, says a study from the University of Texas Department of Health and Physical Education. Unless younger subjects are heavily involved in exercise, they cannot not beat the reaction times of physically fit older men.