New research sheds light on how running and rapid eye movement (REM) sleep enhance communication between the left and right cerebral hemispheres.
A first-of-its-kind study in rats and mice conducted by Omar Ahmed’s Lab at the University of Michigan found that when a laboratory mouse or lab rat runs quickly on a spinning wheel, its left and right cerebral hemispheres commence rapid-fire communication on a specific electrical frequency (140-Hz rhythms) within a single theta cycle.
The researchers also found that when lab animals who run on a spinning wheel during waking hours enter a REM sleep phase, their left and right brain hemispheres communicate on the same 140-Hz frequency. These findings (Ghosh et al., 2022) on how running and REM sleep facilitate better interhemispheric communication between “left brain-right brain” were published on July 5 in the peer-reviewed journal Cell Reports,
Running and REM Sleep Turbocharge Left Brain-Right Brain Communication
As someone who’s been a long-distance runner since 1983, I realized many moons ago that running often creates a waking dream state. If my daily jog takes me off the beaten path and is more adventurous than usual, I often dream about that day’s run in my sleep. Most dreaming occurs during REM sleep as part of a whole-brain process that facilitates the consolidation of long-term memories and mastery of skills practiced the previous day.
When I wrote The Athlete’s Way in the early aughts, an entire subsection of “The Brain Science of Sports” chapter was dedicated to the parallels between brain states that occur during bipedal aerobic activity and REM sleep. On an EEG, the brainwaves that occur during REM sleep and the brain’s low-voltage, high-frequency state when someone’s “in the zone” during a cardio workout mirror one another.
Over the past four decades, I’ve learned via lived experience that running changes how my brain works. When I’m in the zone and enter a state of frictionless flow during a run, the fluidity of my body’s movements and the fluidity of my mind’s thinking seem to go hand in hand. Running helps me connect the dots between seemingly unrelated ideas, boosts cognitive ability, and improves problem-solving abilities.
In addition to promoting creative thinking, jogging makes my brain ripe for having “Aha!” or “Eureka, I’ve found it!” moments. But why? How does running alter brain function, and why does running promote superfluid thinking? For years, I’ve speculated that running optimizes the functional connectivity between the brain’s four hemispheres in ways that help us think better.
The cerebrum and cerebellum both have left and right hemispheres. Colloquially, the term “left brain-right brain” refers to the cerebral hemispheres. Current research tends to focus on interhemispheric communication between the cerebrum’s two halves, but the cerebellar hemispheres are increasingly a region of interest for neuroscientists.
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When I refer to the brain’s four hemispheres, I’m talking about both cerebral hemispheres (colloquially known as left brain-right brain) and both cerebellar hemispheres. The cerebellum (Latin “little brain”) has two hemispheres that are tucked beneath the cerebrum (Latin “big brain”). Most interhemispheric brain research focuses solely on the interplay between the two cerebral hemispheres. Deciphering the interhemispheric dynamics between left brain-right brain is key to understanding how we think.
140-Hz Brainwaves Act Like Spline Gears
The latest (2022) research suggests that turbocharged left brain-right brain communication during running and dreaming is facilitated by 140-Hz rhythms that drive rapid and extremely precise neuronal firing across cerebral hemispheres.
Ghosh et al. (2022) call the 140-Hz brain rhythms that occur at distinct points in a single theta cycle “splines” because they coordinate neural communication like interlocking teeth on mechanical gears. When a lab animal runs or enters a REM sleep phase, splines boost whole-brain functions by improving interhemispheric cortical communication between “right brain-left brain.”
Source: Ghosh et al., 2022 Cell Reports/Open Access (CC BY-NC-ND 4.0)
Like a well-oiled machine, the 140-Hz brainwave frequency acts like a spline gear that allows both halves of the cerebrum to coordinate seamlessly and communicate rapidly without any friction or viscosity. Hence, Omar Ahmed’s Lab calls the neuronal rhythms that promote better interhemispheric communication within one theta cycle “splines” because they resemble the interlocking teeth on mechanical gears and give the brain more torque.
“These spline brain rhythms are faster than all other healthy, awake brain rhythms,” first author Megha Ghosh said in a July 2022 news release. “Splines also get stronger and even more precise when running faster. This is likely to help the left brain and right brain compute more cohesively and rapidly when an animal is moving faster and needs to make faster decisions.”
“Previously identified brain rhythms are akin to the left brain and right brain participating in synchronized swimming: The two halves of the brain try to do the same thing at the exact same time,” senior author Omar Ahmed added. “Spline rhythms, on the other hand, are like the left and right brains playing a game of very fast and precise ping pong.” This neural ping pong represents a different way for the left brain and right brain to communicate.
Optimizing interhemispheric communication improves whole-brain functions. From an evolutionary perspective, it makes sense that the mammalian brain has survival-promoting spline mechanisms that enable both cerebral hemispheres to work in unison like a well-oiled machine when an animal is on the go (hunting, foraging, evading predators) and needs to think fast. Because the brain uses REM sleep to encode memories and weaves the previous day’s lived experience into dreams, it’s not surprising that these 140-Hz brainwaves reappear during dream-state sleep.
What Are the Clinical Implications of Spline-Driven Brain Communication?
Clinical depression, post-traumatic stress disorder (PTSD), and Alzheimer’s disease are all associated with impaired interhemispheric communication. Now that Ahmed and colleagues have identified splines as the rhythmic signature of optimal left brain-right brain communication, future research will explore if splines can be used as a biomarker to diagnose the severity of interhemispheric communication impairments on a continuum.