Wednesday, November 25, 2015

Pain Perception & The Science of Meditation


Why and how meditation affects pain perception is super interesting - per previous well-controlled studies & oodles of patient self-report, it seems to work well for acute & chronic pain situations (the original 8-week clinical MBSR course was developed at least partially with pain control in mind - go read about it in Jon Kabitt-Zinn's Full Catastrophe Living).

A new study from Fadel Zeidan's group (out of Wake Forest) came out recently in the Journal of Neuroscience - it expands nicely on his previous work looking at mindfulness meditation & pain perception (slides from a talk I gave on previous paper below). Basically, the take-home from their related work in 2011 was that 4 days of mindfulness training reduced pain perception and altered pain-related brain activity, especially in the anterior cingulate cortex & anterior insula.



Brain Mechanisms, Pain Modulation, & Mindfulness Meditation from ataren

A question that we have to consider in any intervention is how much of this effect could actually be placebo. To my mind, for practical purposes it doesn't matter much - a placebo effect is still an effect, and when you're talking about reducing pain, I don't always really care how or why I'm perceiving less pain - just that I am.

But determining how much of a given benefit is due to the "placebo effect" can be important for a number of other reasons. Say we're evaluating an intervention with potential harmful side effects  - if a sham would make me feel just as good and is safer/easier, it would be bad practice to keep using the intervention when there are potential downsides involved. 

Another good reason to figure out whether meditation's efficacy for reducing pain is different from placebo has to do with determining mechanisms. The initial Zeidan study got us started - brain regions associated with pain reduction are also activated by mindfulness meditation during a noxious stimulus. And the whole reason we try these interventions is to be able to apply them, so from here, one might say, "we can use meditation to treat people in pain! Not only do people report that they feel better, it does XYZ to your brain, and a placebo doesn't!" Which would be marvelous. Pain is hard to treat. And importantly, comparison to placebo/sham treatment is still the gold standard for showing that any intervention is worthwhile.

With that in mind, what Zeidan et al. have now done is take 75 healthy, normal people and assign them to 1 of four conditions: 4 days of mindfulness meditation, "sham" meditation (basically, being instructed to sit quietly and "meditate", no mindfulness encouraged), placebo analgesic cream, or nothing (control), with before and after fMRI scans. As in the previous study, they used a painful stimulus (heat), and had people rate both pain intensity and pain unpleasantness (physical and emotional perceptions, respectively). And as before, mindfulness meditation was associated with greater activity in brain areas involved in pain modulation (e.g. orbitofrontal cortex, subgenual ACC, anterior insula).

Here's where things get interesting: all interventions reduced pain (mindfulness, sham meditation,
placebo cream). Compared to sham meditation & placebo, mindfulness meditation produced the biggest reductions in pain intensity (-27%) & unpleasantness (-44%) ratings. And importantly, we can now see that there are different brain mechanisms involved:
- sham meditation: no big diffs in neural activity. but reduced respiratory rate - so perhaps a sympathetic nervous system "calming" effect?
- mindfulness meditation: greater activity in brain areas involved in pain modulation (e.g. orbitofrontal cortex, subgenual ACC, anterior insula) --> greater top-down regulation of pain?
- placebo cream: greater dorsolateral prefrontal cortex activation, less somatosensory cortex activation --> dampened activity in sensory pain processing regions

Ergo, "mindfulness-related pain relief is mechanistically distinct from placebo analgesia".

And mechanistically distinct in ways that have some meaningful larger implications - let's extrapolate a bit. Mindfulness meditation requires you to be cognitively engaged, and we see this in the pattern of brain activity shown here, which suggests greater top-down pain modulation with mindfulness (translation: higher order brain regions are exerting influence over your more primitive sensory processing areas. Better "self control" of pain). Mindfulness was also associated with the greatest reductions in perceived pain intensity and unpleasantness. So greater cognitive engagement = brain better at self-regulation of pain = less pain.

In comparison, slapping on a placebo analgesic cream is fairly passive. That's reflected in the fact that one of the main neural findings (consistent with previous brain imaging studies of placebo meds) is of reduced activity in secondary somatosensory cortex, which is responsible for your bread-and-butter sensory stimulus processing. The placebo did also reduce pain intensity & unpleasantness ratings, albeit to a lesser degree. So, cognitive engagement not required = passive/lower-order brain pathways = not-as-good pain control.

In sum: your mind is a powerful thing - use it. Meditation is one way to train the mind, and may in the process bump up your pain perception threshold...and maybe, by extension, your 40k time trial performance :)

photo credit: Reigh Front Pia via photopin (license)

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