Why does training in mindfulness meditation help patients manage chronic pain and depression? In a newly published neurophysiological review, Brown University scientists propose that mindfulness practitioners gain enhanced control over sensory cortical alpha rhythms that help regulate how the brain processes and filters sensations, including pain, and memories such as depressive cognitions.
The proposal, based on published experimental results and a validated computer simulation of neural networks, derives its mechanistic framework from the intimate connection in mindfulness between mind and body, since standardized mindfulness meditation training begins with a highly localized focus on body and breath sensations. This repeated localized sensory focus, the scientists write, enhances control over localized alpha rhythms in the primary somatosensory cortex where sensations from different body are "mapped" by the brain.
In effect, what the researchers propose in their paper in Frontiers in Human Neuroscience, is that by learning to control their focus on the present somatic moment, mindfulness meditators develop a more sensitive "volume knob" for controlling spatially specific, localized sensory cortical alpha rhythms. Efficient modulation of cortical alpha rhythms in turn enables optimal filtering of sensory information. Meditators learn not only to control what specific body sensations they pay attention to, but also how to regulate attention so that it does not become biased toward negative physical sensations such as chronic pain. The localized attentional control of somatosensory alpha rhythms becomes generalized to better regulate bias toward internally focused negative thoughts, as in depression.
"We think we're the first group to propose an underlying neurophysiological mechanism that directly links the actual practice of mindful awareness of breath and body sensations to the kinds of cognitive and emotional benefits that mindfulness confers," said lead author Catherine Kerr, assistant professor (research) of family medicine at the Alpert Medical School and director of translational neuroscience for the Contemplative Studies Initiative at Brown.
Experimental evidence
In experiments that Kerr and neuroscientist co-authors Stephanie Jones and Christopher Moore have published over the last few years, the team has used a brain imaging technology called magnetoencephalography (MEG) to show that alpha rhythms in the cortex correlate with sensory attention and that the ability to regulate localized alpha brainwaves on a millisecond scale is more distinct in people who have had standardized mindfulness training than in those who have not. The trio led these experiments at the Massachusetts Institute of Technology, Harvard, and Massachusettes General Hospital before they all came to Brown in 2011.
In one experiment published in the Journal of Neuroscience in 2010, they observed that when people focused their attention on sensations in the left hand, the corresponding "map" for the hand in the cortex showed a marked drop in alpha wave amplitude (as if to reduce filtering there). When the subjects' attention shifted away from that body part, the alpha rhythm amplitude in the corresponding brain map went back up (as if restoring the alpha filter). Other research groups have shown this to be the case for other kinds of attention-related tasks including focusing spatial attention and working memory.
Then in 2011 in Brain Research Bulletin, the team published another paper. They randomized subjects to eight weeks of mindfulness training versus a control group. In MEG, they asked members of each group to focus attention on sensations in their hand and then to switch their attention to their foot. The people trained in mindfulness displayed quicker and larger changes in alpha wave amplitude in their brain's hand map when they made the attentional shift than the six people who did not have mindfulness training.
Mindful computational model
In addition to the emerging experimental evidence, the research framework is also informed by a computer model that Jones has developed to simulate the alpha brainwaves through reciprocal interactions between the cortex, which processes information and thoughts, and the thalamus, which is like a switchboard that mediates information flow from the rest of the brain to the cortex. The model is well validated in that it produces alpha rhythms that closely match those observed in live MEG scans of real subjects.
Jones, assistant professor (research) of neuroscience, did not originally develop the model to aid meditation research.