Neuroscientists find evidence meditation changes how fluid moves in the brain

A new study published in the Proceedings of the National Academy of Sciences provides evidence that a specific style of meditation may alter the circulation of fluids within the brain. The findings suggest that focused attention meditation can induce changes in cerebrospinal fluid dynamics that are similar to those observed during sleep. This research suggests that mental training might offer a non-invasive method to support the brain’s waste clearance systems.

The study was led by Manus Donahue, a professor of Neurology at Vanderbilt University Medical Center. Donahue and his colleagues sought to understand if waking states could influence the movement of neurofluids. Brain health relies heavily on the efficient circulation of cerebrospinal fluid and interstitial fluid. These fluids work together to maintain a stable environment for brain cells.

They also play a vital role in clearing out metabolic waste products. During the day, the brain accumulates toxic proteins and other byproducts of neural activity. If these substances are not removed effectively, they can build up over time. The accumulation of such waste is linked to neurodegenerative conditions like Alzheimer’s disease and Parkinson’s disease.

Current scientific understanding holds that this cleaning process is most active during sleep. During deep rest, the brain’s fluid channels widen, allowing for a more thorough washout of toxins. However, the ability to regulate this flow during waking hours has been largely unexplored. The researchers hypothesized that the physiological state of deep meditation might mimic some of the restorative functions of sleep.

To test this hypothesis, the researchers recruited a group of 23 adept meditators. These participants were not casual practitioners. They had accumulated an average of more than 3,700 hours of lifetime meditation practice. Their expertise was required to ensure they could enter and sustain the specific mental state needed for the experiment.

The researchers also recruited two control groups of healthy adults. These control participants had little to no experience with meditation. One control group was used to check the repeatability of the brain scans. The second control group was used to test the effects of breathing changes alone.

The researchers employed magnetic resonance imaging (MRI) to observe the brain in real-time. The primary focus was on the cerebral aqueduct. This is a small, fluid-filled canal located deep within the brain. It serves as a major pathway for cerebrospinal fluid to move between different brain chambers.

The expert meditators underwent MRI scans during two distinct conditions. First, they were instructed to engage in a “mind wandering” state. They rested with their eyes closed and allowed their thoughts to drift naturally without focusing on anything specific. This provided a baseline measurement of their fluid flow.

Following this, the meditators engaged in a “focused attention” style of mindfulness meditation. They were instructed to direct their attention to the physical sensations of their breath. They focused on the air moving in and out at the tip of the nose or upper lip. If their mind wandered, they gently returned their attention to the breath.

The imaging techniques allowed the scientists to measure the velocity and volume of fluid moving through the aqueduct. Cerebrospinal fluid flows in a pulsatile manner, driven largely by the heartbeat and respiration. With every heartbeat, blood rushes into the brain, pushing fluid out. When the heart relaxes, the fluid moves back.

The researchers analyzed the “regurgitant” flow of the fluid. This refers to the amount of fluid that flows backward against the primary current during the heart’s relaxation phase. In aging brains, this back-and-forth motion tends to become chaotic and less efficient. Ideally, the net flow should be smooth to facilitate waste removal.

The results showed a change in fluid dynamics during the meditation sessions. When the expert meditators switched from mind wandering to focused attention, the absolute flow of fluid decreased. This was driven by a reduction in the backward, regurgitant flow. The fluid movement became more efficient and coherent.

This pattern stands in contrast to what is typically seen in older adults or those with neurodegenerative diseases. In those populations, fluid motion often becomes hyperdynamic and turbulent. The meditation practice appeared to calm this turbulence. It shifted the fluid dynamics toward a profile more associated with younger, healthier brains.

The researchers also analyzed signals from the fluid near the base of the skull. They looked for rhythmic fluctuations in the MRI signal. During the focused attention state, they observed an increase in low-frequency power. These slow, rhythmic pulses were not present during the mind wandering state.

These low-frequency oscillations are characteristic of non-rapid eye movement sleep. During deep sleep, slow brain waves synchronize with blood flow and fluid movement to pump waste out of the brain. The study suggests that focused attention meditation generates a similar coupling of biological rhythms. The signals from the fluid became synchronized with blood flow signals in the brain’s gray matter.

To ensure these results were unique to meditation, the researchers examined the control groups. One control group simply rested for two consecutive scans. Their fluid dynamics remained unchanged, showing that the MRI measurements were stable. The second control group performed a breathing exercise.

This second control group was asked to slow their breathing to match the rate of the meditators. Slower breathing is known to affect pressure in the chest and head. The researchers needed to confirm that the changes in fluid flow were not caused solely by respiration. The results clarified this distinction.

While the control participants successfully slowed their breathing, they did not show the same changes in fluid flow efficiency. The reduction in regurgitant flow seen in the meditators was absent in the breath-control group. This indicates that the physical act of breathing slowly is not enough to alter neurofluid dynamics on its own. The mental state of focused attention appears to be a necessary component.

The study provides evidence that the brain’s waste clearance system can be modulated consciously. It links the mental practice of mindfulness to tangible physical changes in intracranial fluid mechanics. This offers a potential mechanism explaining why meditation is often associated with improved cognitive health.

However, like all research, the study does have some limitations. The sample size of adept meditators was relatively small. Recruiting individuals with thousands of hours of experience is a challenge for clinical research. This makes it difficult to know if the results would apply to beginners.

The study was also cross-sectional rather than longitudinal. It looked at a snapshot in time rather than following participants over years. It is not yet known if these short-term changes lead to long-term health benefits. We do not know if regular meditation prevents the buildup of Alzheimer’s-related proteins.

The researchers also noted that the MRI scans have limits in temporal resolution. Biological signals happen very fast. The scans captured data roughly once every second. Some faster physiological interactions might have been missed.

Future research will aim to address these gaps. The researchers suggest exploring different styles of meditation to see if they produce similar effects. Practices that involve open monitoring or compassion might yield different physiological profiles. Longitudinal studies will also be needed to track brain health over time.

This line of inquiry could eventually lead to new therapeutic interventions. If meditation can indeed boost the brain’s cleaning cycle, it could be prescribed as a preventative measure. It would serve as a non-pharmacological tool to combat neurodegenerative decline. The study opens the door to viewing meditation as a form of physiological maintenance for the brain.

The study, “Neurofluid circulation changes during a focused attention style of mindfulness meditation,” was authored by Bryce A. Keating, David Vago, Kilian Hett, Ciaran Considine, Maria Garza, Caleb Han, Colin McKnight, Daniel O. Claassen, and Manus J. Donahue.