What Causes the Brain to Have Slow Processing Speed, and How Can the Rate Be Improved?—Heather Walker, via email
Geoffrey A. Kerchner, assistant professor of neurology and neurological sciences at the Stanford University School of Medicine, responds:
To a brain scientist, processing speed means just that: the rate at which a human can take in a bit of new information, reach some judgment on it and then formulate a response. Studies suggest that the speed of information processing changes with age along an inverted U-shaped curve, such that our thinking speeds up from childhood to adolescence, maintains a period of relative stability leading up to middle age, and finally, in late middle age and onward, declines slowly but steadily.
That processing speed slows with age is intuitive to most people. Many elderly individuals have noticed that it takes them longer to solve problems or make decisions than it did when they were young. Yet the reasons for this age-related deceleration in information processing are not completely understood and may vary from person to person. Some compelling evidence suggests that such a decline reflects wear and tear of the white matter in the brain, which is made up of all the wires, or axons, that connect one part of the brain to another. Slowed information transfer along axons may impede processing speed. But what causes this axonal communication to slow down in the first place?
In some people, diabetes, smoking, high blood pressure or other so-called vascular risk factors can wear away at the blood vessels feeding the brain's white matter, starving axons of much needed oxygen and glucose. Some people may have a genetic predisposition to age-related white matter decay, a poorly understood but actively studied hypothesis. In other individuals, slowed processing speed could be the first sign of a neurodegenerative illness, such as Alzheimer's disease. Head trauma, including concussions, may play a role. These are a few of the many ideas out there—other factors surely remain to be discovered.
More important, slowed information processing affects almost every aging adult to some degree, and the line between normal and abnormal is fuzzy. A person may sustain or even improve information processing speed by paying close attention to vascular risk factors, engaging in regular aerobic exercise, eating well and continuing to challenge oneself intellectually.