A new window into exercise’s impact on the brain

New research provides evidence that the brain’s arousal system plays a role in the cognitive benefits of exercise. The findings, published in NeuroImage, also indicate that pupil diameter changes could potentially serve as a predictive marker for exercise-induced cognitive improvements, providing a novel way to understand the effects of exercise on the brain.

Previous research had shown that very light-intensity exercise, such as yoga or slow running, could improve cognitive performance without causing stress or negative mood responses. However, the underlying neural mechanisms for this improvement were not well understood. The researchers were particularly interested in understanding how the brain’s arousal system, specifically the catecholaminergic system originating from the locus coeruleus (LC), might be involved in the beneficial effects of exercise on executive function.

“The COVID-19 pandemic has reduced our physical activity, which may result in severe cognitive and mental health decline,” said study author Hideaki Soya, a professor at the University of Tsukuba.

“As a countermeasure, stress-free mild exercise, such as yoga, tai-chi, and slow mindful running, is a potent treatment candidate for brain health. We have shown in animal and human translational studies that exercise stimulates brain function even at stress-free very light intensity. However, the technology does not exist to read real-time brain activity during very light exercise in humans. For this reason, the current study focused on the pupil in the eye, known as the window to the mind.”

To conduct the study, the researchers designed an experiment involving healthy young adults. The study’s sample consisted of 34 participants, of which 6 were female and 28 were male. The researchers recruited participants who had no self-reported history of neurological or psychiatric disorders. They aimed to select individuals who were relatively healthy and free from conditions that could confound the study’s results.

The study followed a crossover design, where participants underwent two conditions on separate days: a resting control (CTL) condition and a very-light-intensity exercise (EX) condition. In the EX condition, participants engaged in 10 minutes of very light-intensity cycling exercise, while in the CTL condition, they rested. The exercise load was individually tailored to each participant’s aerobic capacity.

The researchers employed a combination of techniques to gather data during the experiment. Pupil diameter was continuously measured using an eye-tracking device, which provided insight into changes in arousal and cognitive states. Functional near-infrared spectroscopy (fNIRS) was used to monitor prefrontal cortex activity during an executive function task known as the color-word Stroop task. This task involves responding to color names presented in incongruent colors, requiring cognitive control to overcome interference.

The study revealed that pupils dilated during very light exercise and that the extent of this dilation was associated with subsequent improvements in executive function performance. This dilation of pupils was linked to the brain’s noradrenergic arousal system, particularly the LC.

“When we first saw the raw pupil diameter data, we were amazed by the drastic dynamic change from rest to light exercise,” Soya said. “In the old days, it was said, ‘No pain, no gain.’ However, it was interesting that we could clearly confirm in the pupil raw data that the brain is activated even by very light-intensity exercise in humans.”

The fNIRS measurements indicated an increase in activity in the left dorsolateral prefrontal cortex during the executive function task after exercise. This region of the brain is known to be involved in executive functions such as cognitive control and decision-making.

The findings indicate that “even 10 minutes of very light exercise can enhance the function of the prefrontal cortex,” Soya told PsyPost. “This is good news for those who dislike exercise.”

“Also, the pupil reflects the brainstem’s activity, including the brain’s noradrenergic arousal system. In the present results, pupils were sensitively dilated during exercise, which predicted improved prefrontal cortex function. The visualization that the brain arousal states for improved prefrontal cognition during very light exercise is new in human participants. Furthermore, looking ahead, pupil observation holds promising potential as a novel biomarker that can be used to predict the effects of exercise on the brain.”

But the study, like all research, includes some caveats.

“It is important to note that our experiments are strictly controlled to light and visual stimuli for experimental validation,” Soya said. “Pupils strongly reflect the effects of visual information, so care should be taken when applying current results practically.”

“We are researching the neuroscientific mechanisms of the impacts of exercise on the brain, especially mild exercise,” the researcher added. “We encourage you to check out other studies that have been done and start very light exercise today.”

The study, “Pupil dynamics during very light exercise predict benefits to prefrontal cognition“, was authored by Ryuta Kuwamizu, Yudai Yamazaki, Naoki Aoike, Taichi Hiraga, Toshiaki Hata, Michael A. Yassa, and Hideaki Soya.

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