Sometimes, writing about how meditation changes the brain feels just like a certain classic Far Side cartoon: a complex science or math problem is being solved, with an impressive opening salvo and a promising conclusion, but a certain fuzziness about an intermediate step where “a miracle occurs”. A professor colleague and I have dubbed this “handwaving”, based on the gesture that accompanies “and then chemistry” (or other scientific discipline of your choice) for introductory courses.
I imagine my beginning students are relieved not to be burdened by the complex intermediate steps, but it’s also incredibly frustrating when you can’t see behind that hand when you’re ready. Meditation practices can actually change the activity in our brain and the very action of your genes, in a matter of weeks. The start is the focused brain state we can achieve with meditative practices; the end is a change the structure of our neurons. But what is the “miracle” in between? Clearly, something must be going on in the neurons, the building blocks of the brain. But what is changing, and what causes it to change?
The answer may come from a technique called diffusion tensor imaging, shortened to DTI. This technique uses our friend the MRI machine in a different way than most psychologists tend to. Normally, psychology is all about the functional MRI (or fMRI), which tracks the flow of oxygen through blood vessels in the brain to determine which areas are using the most oxygen and therefore probably doing the most work. In contrast, DTI tracks water molecules, which exist inside the neurons themselves and move differently when they are in the blood, in a neuron, or even in different parts of a neuron.
For understanding how neurons communicate with each other, two parts are vitally important. One is the like the axon, which is the long protrusion that extends from one neuron and reaches to the next, whether it’s right next door or all the way down your spine. The electrical message that neurons use to communicate has to travel down this axon. The other part is the myelin sheath, which wraps around the myelin to protect it and help the message spread faster. You can think of the axon as being like a telephone wire, and the myelin as being like the plastic coating that goes around the telephone wire. Together, these parts make up the “white matter” of your brain, which contributes to your mental health and intelligence by allowing different regions of your brain to talk to each other.
Essentially, DTI allows researchers to track changes in white matter, such as the structure of the axon itself and of the myelin surrounding it. This is what researchers led by Yi-Yuan Tang did just a few years ago, showing that 30 minutes of “integrative mind-body training” each night for a month improved both the size of the axons (measured through “axial diffusivity”) and the myelin coating (“radial diffusivity”) in a region of the brain important for self-regulation.
Now, those researchers have collected together bits and pieces of different information to create a theory for just how meditation training could lead the white matter of the brain to change itself, in just a few weeks.
The first step is that meditative states produce what’s called a “theta rhythm”. The different “rhythms” of the brain are a measure of how your neurons are firing in sync with each other; we tend to have “beta” rhythms when we’re awake, “alpha” waves when we’re very relaxed or falling asleep, and “delta” waves when we’re deeply asleep. “Theta” waves appear during light sleep, including REM sleep (when we’re dreaming), and during meditation. Being in a theta rhythm state appears to excite the neurons, and to lead them to produce something called calpain.
Calpain is a protease (pro-TEE-ace, not a professional tease), basically a chemical that helps the neuron grow and change and is important for helping the neuron form new synapses or connections with other neurons. It may help widen the axon, or do something slightly more complicated to tweak the myelin. to help the neuron send its message faster.
Obviously, there’s still some handwaving in this new explanation, around the point where calpain actually does something to that axon to cause the white matter to grow. But it’s handwaving when zoomed in to a much closer picture of the neuron, where theta states trigger enzyme production before any handwaving begins, and narrows “brain change” to specific adjustments in axons and myelin. I’m happy to root for a theory that suggests such precise mechanisms, and hopeful that enough neurochemists will be intrigued enough to work their own brand of scientific research to find scientific answers to replace this “miracle”.
Posner MI, Tang YY, & Lynch G (2014). Mechanisms of white matter change induced by meditation training. Frontiers in Psychology, 5 PMID: 25386155