Most of my previous explorations of how meditation changes the brain have been based on what’s called functional MRI, which look at the activity in the brain in a given scenario: how meditators’ brain activity when they’re resting is different from non-meditators, or how deciding to be altruistic is correlated with more activity in regions like the inferior parietal junction. These changes are usually assumed to go hand-in-hand with actual physical changes to the structure of the brain, which alter the routes by which information is able to travel in the brain. As usual in science, these are assumptions that should be tested.
Investigating changes in the physical structure of the brain is accomplished with a much more detailed MRI picture – the kind your doctor might use to get a clear look at the structure of your knee or your spine for a physical injury. A finely tuned picture like this lets us make distinctions between different brain regions, and also between the gray matter and white matter within those regions. “Gray matter” does actually look ash-gray under a microscope; it’s composed of neuron’s cell bodies and synapses, as well as the supporting network of glia that help keep neurons alive. “White matter” does indeed look white, thanks to the myelin sheath around the axons; you can think of it as the interstate system that connects different regions of the brain together.
A basic schematic of a neuron. The cell body and dendrites form the “gray matter”, the myelinated axon forms “white matter”.
To look for changes in gray matter resulting from meditation, sixteen (mostly white, mostly well-educated, but at least ranging in age up in the 50s) volunteers took a classic Mindfulness Based Stress Reduction (MBSR) workshop, while a similar group who had expressed some interest in taking the MBSR course just went about their daily lives. Before and after the 8 week course, everyone had a brain scan, and completed the Five Facet Mindfulness Questionnaire (the facets being tendencies to observe, describe, act with awareness, be non-judgmental, and be non-reactive).
Behaviorally, the MBSR course seemed to improve the volunteers’ scores for observing, acting without awareness, and non-judging. How much, we can’t say, because the researchers reported on the statistics without any average scores or even effect sizes. I’m starting to wonder if I will always have this pet peeve with brain research, which often seems to gloss over the behavioral results beyond a “yep, seen as expected”, possibly to save room for all the detail needed for the neurological results. I can kind of understand, but I can also see that the control group had a nearly-significant improvement on acting with awareness (p = .068, just a hair over the usual p < .05 cutoff) which seems a little artfully buried in a string of statistics. Knowing more about the averages and ranges of responses might also clarify why there were never any relationships between how much an individual’s mindfulness changed, or how much they practiced outside of class, and changes in the brain. You’d expect that the greater the behavioral improvements or time on task, the greater the brain changes; I can think of a few statistics-related reasons for not finding a link (basically, not enough variability in what people did), but I need the numbers to know if that’s it.
Looking solely at the brain structure changes, though, we can see intriguing growth in two brain regions of the default network:
- The hippocampus, or more precisely a small piece of the left hippocampus. Although it is now primarily known by its role in memory (thanks to the famous patient H. M.), it seems to contribute to our usual mind-wandering and sense of self through the recall of autobiographic memories. It’s also important to note that stress hurts the hippocampus, so the changes observed might not be about the “mindfulness-based” component but the “stress reduction” of MBSR, with reduced stress allowing the recovery of the hippocampal neurons.
- The posterior cingulate cortex, where information about ourselves and our surroundings are integrated.
We also see an increase in another brain region previously associated with meditation:
- The left temporo-parietal junction, linked to how well we understand other people and linked with mindfulness-based improvements in altruism.
And finally, a surprise player:
- Two small nuclei in the cerebellum, usually thought of as just being responsible for coordinating muscle movements throughout the body, but recently getting recognition for its role in a much broader array of behaviors; in this case, the researchers speculate that it may help coordinate the physical reactions linked to emotional processes, which would potentially be changed by meditation.
What does it mean that they gray matter volume in these regions increased? That depends on what part of the gray matter grew. It could just be that there were more synapses, meaning more connections between one neuron and the next, allowing for different patterns of communication within and between these brain regions that could lead to behavioral changes. On the other hand, It could have been that there were more cell bodies, meaning more neurogenesis (birth of new neurons), which is a rather more dramatic and exciting option. And of course, it could be a combination of both. (And we shouldn’t forget the possibility that these changes are due to glia, but since glia are the neglected workers of the brain it’s harder to know what those changes might be or what impact it would have).
I’m personally curious whether the same changes are happening in each brain region; it’s easier to imagine neurogenesis in the hippocampus, which was the first place that we saw new neurons being born in an adult brain, with perhaps just some new or rearrange synapses taking place in other regions. Fine-tuning this research to determine exactly what’s happening with the gray matter, and linking changes to more than just taking a class will take some work….but perhaps eventually we’ll see that meditation is a way to help our brains literally grow.
Hölzel, B., Carmody, J., Vangel, M., Congleton, C., Yerramsetti, S., Gard, T., & Lazar, S. (2011). Mindfulness practice leads to increases in regional brain gray matter density Psychiatry Research: Neuroimaging, 191 (1), 36-43 DOI: 10.1016/j.pscychresns.2010.08.006
contemplating cognition 
One of the big problems with this study is the control group is not good for comparison to see if these changes can really be attributed to mediation. The intervention involved weekly group meetings, yoga, and a pretty intensive schedule to facilitate stress reduction. Any/all of these things could have some effect on brain structure/function, and so it would make sense to have a control group that was engaged in some similar practices that weren’t mindfulness-based. As far as I can tell, they didn’t even use concurrent controls here, and got their control sample (or at least part of it) from a 2008 study done in Germany. Interesting article, though – thanks for the write-up!
I call this kind of design a “sledgehammer”, or throwing everything but the kitchen sink into the experimental condition. It’s not ideal, but sometimes it makes sense as a first step, when you want to demonstrate that change is even possible. Throwing every possible thing into an intervention allows us to be confident that the intervention is doing something, compared to doing nothing; more fine-tuned studies (using a “scalpel”) later will tell us what the source is.
I like your metaphor of a sledgehammer vs a scalpel! :-)
I can have a lot of fun with that metaphor. Too much fun, perhaps. Imagine a scientific problem as a wall that is blocking us from seeing; we want a window through that wall. Starting with a scalpel (or similar construction equipment) would mean thousands of cuts and a ridiculous amount of effort without even knowing what’s on the other side. Starting with a sledgehammer, though, will quickly show you whether the view through the wall is something that you want to see; you then use the scalpel to neaten up the edges of your hole and find the true shape of the window. And I end up with a strong temptation to bring drywall and tools to a research methods class.
I find this research extremely interesting. Just like in other studies, I think before it is stated as fact, more tests need to be done that have more information such as the average number of people that had increased gray matter or the size of the effects. I would be interested to see what other areas of the brain that the gray matter increased in. Possibly the temporal lobe of the cortex? More specifically, the amygdala. I would also be interested if more information could be found using other tests other than an MRI such as an EEG or PET. Nonetheless, it is extremely interesting that simple mediation exercises and rest can increase the cell bodies in the gray matter and the matter itself. Looks like I found my new hobby :)
The changes everywhere other than the hippocampus were found with what’s called an “exploratory whole-brain analysis”, which means they looked everywhere in the brain (with statistical corrections to make it less likely they would think a difference was significant by chance), so I don’t know that I would expect changes elsewhere from the 8-week MBSR. Just like some of the other functional brain changes I’ve talked about though, it might depend on what kind of practice the participants are doing. Changes in the amygdala might come from a more focused training in loving kindness, perhaps, or other trainings that focus a lot more on emotional responses than just attention. I suspect we will see more and more about gray matter changes under a variety of meditation routines for a decade to come.