Photo by Yogendra Joshi, via Flickr
Photo by Yogendra Joshi, via Flickr
ScienceOnly Human

How 10 Minutes of Mild Exercise Gives Your Brain a Boost

I’m an exercise procrastinator, as I’ve admitted before on this blog. Rationally I know that daily exercise will be good for me in the long run. But it’s hard to get motivated by vague health benefits that are years or even decades away.

Like any good American I like my instant gratification. I found some today in a new brain-imaging study reporting that 10 minutes of mild exercise dials up the brain’s arousal system, making you think faster and smarter.

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Yanagisawa et al., 2010

A team of sports scientists in Japan recruited 25 healthy young people to come into the laboratory on two occasions; in one session they rode a stationary exercise bike for 10 minutes, and in the other they rested instead.

The volunteers took two tests before and after the exercise/rest periods. One of the tests, the Two-Dimensional Mood Scale, measures mood and arousal states: energetic or lethargic? Relaxed or nervous? And so on.

The other was the famous Stroop test, which measures attention and brain-processing speed. The researchers showed volunteers words that describe color (such as red, blue, and green), but asked them to name the color of the letters rather than read the word. It’s a difficult test: When the color of the letters doesn’t match the word [red, blue, green], it takes your brain some time to register the mismatch. (You can try the test for yourself here).

But here’s the cool part of the study: The researchers measured the volunteers’ brain activity while taking the Stroop test (both before and after exercise). They used an imaging technology called functional near-infrared spectroscopy, or fNIRS, in which a cap of harmless optical probes detects color changes in superficial blood vessels. When brain cells respond to a stimulus they use a fresh supply of red blood, replete with oxygen. This activity displaces blue, deoxygenated blood from the region. By measuring these color changes, fNIRS offers an indirect measure of neuronal activity in the brain’s outer layers.

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Byun et al., 2014

The researchers found that during the exercise session, volunteers showed a significant drop in Stroop reaction time after exercise. In contrast, the same people did not show this improvement in the rest session.

Exercise also triggered a surge of brain activity on the left side in two regions: the dorsolateral prefrontal cortex and the frontopolar area (see image above). Both regions are known to be involved in attention and executive function. And the extent of exercise-induced brain activity correlated with the volunteers’ gains in processing speed.

OK, but why? Why does exercise cause these extra buzzings in the frontal cortex?

The researchers suspect the answer lies in the so-called “fight or flight” system — the network of chemical messengers that regulate our arousal patterns and stress responses. Previous studies in rodents have shown that exercise causes the brain to release more acetylcholine, noradrenalin, and dopamine, neurotransmitters that are involved in arousal and are known to activate the frontal cortex. Bolstering this idea, the volunteers in the new study showed higher arousal scores on the mood test after exercising, and these scores correlated with frontal brain activity.

The same group of researchers published a very similar paper in the same journal, NeuroImage, in 2010. In the older study, however, volunteers performed “moderate” exercise: 10 minutes of biking at an intensity requiring 50 percent of their peak oxygen uptake. The new study finds the same benefits with “mild” exercise, defined as requiring just 30 percent of peak oxygen uptake. This is an important distinction, the researchers say. As our lifestyles become more and more sedentary, they write, “it is of considerable importance to determine the lowest level of physical activity required to maintain mental and physical health.” (How about that for a low bar?)

So with that, I’m going to drag myself outside for a run. Hopefully it will make for a cognitively productive afternoon.