The Mindful Brain

White-Matter Changes May Explain Behavioral Effects of Mindfulness Meditation Practices

by Brenda Patoine

May 31, 2016

BRIEFING PAPER

When the Beatles went to India to study Transcendental Meditation at a remote ashram in the 1960’s, meditation was still largely seen in the West as a cultish fad favored by celebrities and hippies. Fifty years later, meditation has gone mainstream.

Mindfulness-based meditation is now firmly established as a valid stress-reduction tool and is backed by a growing body of solid science illuminating its effects on the brain and health. It is being applied to an ever-growing list of conditions and life situations, including keeping kindergarteners calm, boosting job satisfaction, overcoming addiction, and beating back pain. Mindfulness meditation, as Fortune magazine reported in March, has become a billion-dollar business.

The idea that such a seemingly simple practice as mindful breathing–the method essentially boils down to sitting still, focusing on the present moment, and bringing attention to the breath–can alter the structure of the brain and improve health has caught the attention of researchers right along with the public. Like many booming businesses based on emerging science, the claimed benefits of mindfulness practices sometimes run ahead of the science.

What’s clear is that meditation changes the brain in a number of ways, some of them well-characterized. Less clear is how those brain changes translate to health improvements, how much of a “dose” of meditation is needed, or how long the benefits last, among other questions. A looming challenge for the field is how to best apply mindfulness practices to solve real-life problems in schools, homes, and workplaces, and to approach these applications with sound research that tracks the results and informs best practices.

Very few long-term studies have gauged how mindfulness practice affects health over the lifespan, and the few that have show mixed results. The most robust longitudinal data comes from studies in chronic pain, where mindfulness practice shows a clear benefit in pain reduction even years after initial training. Meditation is also associated with less relapse in depression and substance abuse.

The effects are much less clear in healthy populations, simply because the studies have not been done. Still, nearly half of businesses will offer mindfulness training to their employees by 2017, according to forthcoming survey data cited in the Fortune article.

Mindful Students

Schools are jumping on board the meditation train, with organizations training teachers by the thousands to incorporate mindfulness practices into their classrooms, adapted for students from preschool to university. A fewpilotstudies have shown positive benefits among students and teachers, but longitudinal studies to objectively evaluate the enduring effects of school-based mindfulness are only beginning.

“These strategies have never been investigated seriously in children before, but now a number of researchers are doing so,” says Richard Davidson, director of the Center for Investigating Healthy Minds at the University of Wisconsin, Madison, and a prominent researcher in the field. “What we don’t have are really good long-term longitudinal studies with multiyear follow up. That kind of evidence is simply lacking.”

Efforts are underway to close the gap in longitudinal data. Davidson’s center received funding from the U.S. Department of Education to conduct a three-year randomized, controlled trial of mindfulness training among 700 fourth and fifth graders in Madison public schools. In the largest investigation yet of mindfulness in schools, the U.K.-based Wellcome Trust, just launched a seven-year longitudinal study involving 7,000 11- to 16-year-olds to assess the impact of a school-based mindfulness training program, which will include brain scans on 600 of the students.

While the long-term benefits are sorted out, even short-term effects of well-timed mindfulness-based interventions may be useful, says Michael Posner, a professor emeritus of psychology at the University of Oregon and a member of the Dana Alliance for Brain Initiatives. Stress reduction is a good example, he says.

School can be stressful, whether it’s a private prep school or an inner-city public school ravaged by poverty and violence. Young brains are more plastic as they undergo rapid development that makes them more adaptable to environmental influences, good or bad. The hope is that by teaching children healthful ways to manage stress, they can better cope with school in the short term and be more resilient to stress-related diseases and mental health problems over the long term. As Davidson notes, the potential for instilling healthy stress-management habits early on is great.

Making Connections

From a neuroscience perspective, the attraction to apply mindfulness to education stems from how the practice changes the brain. Meditation broadly influences two major brain systems, explains Davidson: attention and emotion. The regulation of these systems is key–the ability to focus attention without distraction in the first case and the capacity to exercise control over emotional impulses in the second.

These effects may be connected to the anterior cingulate, a major hub of the attention circuit that is also involved in cognitive and emotional control, says Posner, who has spent his career studying the attention system.

A recent research focus is how mindfulness practices influence the connectivity among the brain regions that comprise these circuits, Davidson says. “Some of the effects of meditation–some people would say a lot of them–may be on the alterations in connectivity of these circuits, which play important roles in both attention and emotion regulation.”

Connections in the brain are comprised of white matter tracts–myelinated axons that can sometimes stretch long distances to transfer the biochemical signals of activated neurons. They are the telephone cables of the central nervous system. When myelin, the fatty white sheath that envelops axons, degrades, as it does in multiple sclerosis, or is damaged, as in spinal cord injury, the results can be subtle or devastating. Healthy brain function depends on an intact system of white matter tracts with sufficient myelin coating to shuttle brain signals efficiently along the circuit.

Increasing evidence suggests that the better the connectivity in a given brain circuit, the more efficient the circuit. Neural efficiency pays off in many ways, one of which is better cognitive control, which translates into things like staying on task and regulating emotional responses–the same behaviors that mindfulness practice improves.

Scientists can measure the efficiency of white matter tracts in living humans using an MRI technique known as Diffusion Tensor Imaging (DTI). Important pathways connecting the prefrontal cortex to emotional regions in the brain appear to be strengthened by meditation, including the uncinate fasciculus, a key part of the emotion-regulation circuit.

Posner’s team and others have used DTI to show that meditation alters white matter tracts all around the anterior cingulate, and are now trying to understand the mechanisms by which meditation “trains” attention and emotion regulation.

Demystifying the Mechanisms

Posner is focusing on white matter to investigate how a mental activity like mindfulness meditation can influence attention behaviors. His hypothesis–currently being tested in an animal model–is that meditation induces a low-frequency theta brain rhythm (a brain-wave pattern defined as 4-8 cycles per second as recorded on EEG) in frontal brain regions. This particular pattern of nerve-cell firing is known to trigger an enzyme that activates dormant oligodendrocytes, the precursor glial cells that make myelin.

The theory is plausible in light of new research indicating that white matter is more plastic than was previously thought. Animal research from the laboratory of William Richardson at University College London showed that motor learning fairly rapidly activates dormant oligodendrocytes to produce myelin, and that learning is dependent on the activated cells. This idea of “activity-dependent myelination,” which has been replicated repeatedly since McKenzie’s initial report, opens the door to therapeutic approaches that trigger myelin-forming cells to become active.

In an attempt to observe what has been seen in human fMRI studies following mindfulness practice, Posner is working with the Niell laboratory at the University of Oregon and using optogenetics, a technique that uses light to turn genetically modified neurons on and off at will, to induce rhythmic activity in neurons in the anterior cingulate. The researchers put mice into a meditative state characterized by a theta brain rhythm for 30 minutes a day for one month, then characterized the white matter changes around the anterior cingulate. Their preliminary results (not yet published) show that the corpus callosum, the primary inter-hemispheric white-matter cable through which many affected axons pass, is significantly thicker in the treated mice. The team is now using electron microscopy to confirm and expand the initial findings.

This is an elegant example of how science takes a behavioral observation, such as increased attentiveness following mindfulness training, and tracks it backward: first to the brain circuit that is involved (attention-regulation network), next to the type of change within that circuit (improved white-matter integrity), and then to the specific mechanism underlying the change (theta rhythm-induced activation of myelin-forming cells).

It also helps explain why there is so much interest in teaching children mindfulness, as the potential is huge for positively impacting the neural circuitry of attention and emotional regulation systems at an age when the brain is highly plastic and behavioral habits (good or bad) can strongly influence its “wiring-up.”

“The intention of this work is that kids will learn simple practices that will become lifetime habits and be incorporated into their daily life as part of their personal hygiene,” says Davidson. “We envision a time when these kinds of things would be as common as brushing your teeth twice a day.”