Exercise triggers memory-related brain 'ripples' in humans, researchers report

A single session of physical exercise can spawn a boost of neural activity in brain networks that underlie learning and memory, according to a new study led by the University of Iowa.

The researchers measured neural activity in the brains of patients with epilepsy before and after they completed a bout of physical exercise. The results showed that a single exercise session produced in the participants a burst of high-frequency brain waves, called ripples, emanating from the hippocampus to areas of the brain involved in learning and recall.

Neuroscientists have documented ripples relevant to memory in mice and rats, but they had not confirmed the link in humans, mainly because electrodes need to be implanted in the brain to obtain recordings. Instead, researchers had theorized the ripples’ role in humans, based on studies in people that measured changes in oxygenated blood in the brain after exercise. This new study marks the first time researchers have been able to see the neurons in action in people following exercise, the authors report.

The Iowa-led team recruited 14 patients at University of Iowa Health Care Medical Center, between 17 and 50 years of age, to participate. After a brief warmup, participants rode a stationary bike for 20 minutes at a pace they could maintain for the duration. Researchers recorded the participants’ brain activity before and after the cycling session using intracranial electroencephalography (iEEG), which utilizes implanted electrodes to measure neural activity in the brain.

The recordings showed an increased rate of ripples originating in the hippocampus and connecting with cortical regions of the brain known to be involved in learning and memory performance.

"We’ve known for years that physical exercise is often good for cognitive functions like memory, and this benefit is associated with changes in brain health, largely from behavioral studies and noninvasive brain imaging,” says Michelle Voss, professor and Ronnie Ketchel Faculty Fellow in the Department of Psychological and Brain Sciences at Iowa and the study’s corresponding author. “By directly recording brain activity, our study shows, for the first time in humans, that even a single bout of exercise can rapidly alter the neural rhythms and brain networks involved in memory and cognitive function."

Voss says the results apply beyond the epileptic patients who participated.

“The patterns we see after exercise closely match what’s been observed in healthy adults using noninvasive brain imaging, like fMRI. That convergence across very different methods is one of the strongest indicators that the effects are not specific to epilepsy but reflect a more general human brain response to exercise,” she says.

The researchers plan to seek funding to cement the exercise-memory link in the brain by having participants take memory tests after an exercise session as their brain activity is being directly recorded.

The study, “Exercise enhances hippocampal-cortical ripple interactions in the human brain,” was published online on March 9 in the journal Brain Communications, part of Oxford Academic.

Co-lead authors are Araceli Cardenas, from Toronto Western Hospital, who was a postdoctoral researcher in neurosurgery at Iowa; and Juan Ramirez-Villegas, from the Institute of Science and Technology in Austria.

Study co-authors from Iowa are Christopher Kovach, Phillip Gander, Rachel Cole, Hiroto Kawasaki, Jeremy Greenlee, Matthew Howard, and Kirill Nourski.

Other contributing authors are Andrew Grossbach from Ohio State University and Matthew Banks from the University of Wisconsin-Madison.

The research was funded through the University of Iowa.

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