1.Mindfulness Meditation and Brain Activity

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Miller, J. (2008). [Buddhist monk prepares for an EEG].
Retrieved from http://www.news.wisc.edu/newsphotos/davidson08.html

Meditation can refer to a broad variety of practices, which tend to share many similarities. Researchers tend to define meditation using common factors found among different schools of practices, thus meditation can be broadly defined as “a family of self-regulation practices that focus on training attention and awareness in order to bring mental processes under greater voluntary control and thereby foster general mental well-being and development and/or specific capacities such as calm, clarity, and concentration."[1]

While mindfulness practices and meditation are sometimes used interchangeably, some researchers make a distinction between mindfulness-based meditation and other types. For example, one definition of mindfulness-based meditation is the “non-reactive monitoring of the content of experience from moment to moment,” which is distinct from focused attention meditation, the “voluntary focusing of attention on a chosen object."[2] Therefore, mindfulness is distinct from other meditation practices in that it focuses on passively monitoring one's own cognitive and emotional states as they are occurring, as opposed to actively suppressing or altering one's experiences to produce a certain state.

The Mindfulness Experience.

Bishop et al. (2004) proposed a two-component model of mindfulness.[3] In this model, mindfulness is partly achieved by directing the focus of attention to one's own thoughts and feelings from moment to moment, which would require the ability to sustain attention over a long period of time, as well as the ability to switch attention from one point of focus to another. This model also defines mindfulness as adopting a specific orientation towards experience, characterized by curiosity, openness and acceptance. Mindfulness practitioners do not try to produce a particular state or suppress certain thoughts, rather all thoughts, feelings, and sensations that arises are considered relevant and allowed to exist, and the practitioner take notice and observe all of them without judgement.

Bishop et al. (2004) also proposed that the self-regulation of attention promotes non-elaborative processing, as attention is directed to simply acknowledge and observe the present experience, and further processing of the experience is inhibited. This may be associated with improvements in cognitive inhibition, as well as freeing up attentional resources to extract more meaning from the present experience. Monitoring one's own stream of consciousness with an orientation of openness and acceptance also allows for intensive self-observation, and over time lead to increased capacity to distinguish different affective states and physical sensations, as well as generate more complex representations of cognitive and affective experiences.[3] These effects proposed by Bishop et al. may be related to a number of health benefits that have been linked to mindfulness-based practices. For example, promoting non-elaborative processing leads to inhibition of ruminative thoughts, which may have positive effects on someone suffering from mood disorders such as depression. Increased ability to identify and distinguish cognitive, affective, and bodily experiences may also be helpful in reducing pain, anxiety, and identify negative thoughts in a similar manner to cognitive re-framing techniques.

DMN Deactivation

Mindfulness-based meditation and therapies are usually performed in a passive, resting state, where thoughts and emotions arise naturally, without any cognitive effort. Thus, effects of mindfulness practice is closely related to activity of the default mode network (DMN), which are brain regions active during resting state or internal cognitive tasks, and include regions in medial temporal lobe, medial pre-frontal cortex (mPFC), and posterior cingulate cortex (PCC).[4] Activity of the DMN has been shown to correlate with the generation of stimulus-independent thoughts (mind-wandering),[5] as well as maladaptive, depressive rumination.[6]

Decreased DMN activation in
experienced meditators
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Brewer J A et al. PNAS 2011;108:20254-20259

Research have shown that mindfulness-based meditation is correlated with reduced activity in key nodes of the DMN. Brewer et al. (2011) examined cortical activity in experienced meditators and non-meditator controls while they performed 3 kinds of mindfulness meditation, and found that the PCC, mPFC, as well as superior, middle, and medial temporal gyri and uncus were less activated in experienced meditators compared to controls during meditation.[7] Meditators also reported less mind-wandering compared to controls.

Deactivation of key regions of the DMN may contribute to the experience of mindfulness: a meditator can experience calmness and increased focus without active suppression of certain thoughts or distractions, which may be related to reduced DMN activity and thus less generation of wandering thoughts. As well, reduced activity of the DMN may be related to reduced maladaptive ruminative thoughts,[6] which matches the inhibition of elaborative processing in mindfulness practices, and potentially explaining the health benefits associated with mindfulness meditation such as alleviating stress and depressive symptoms.

Coactivation of PCC, dACC, and dlPFC
at baseline and during meditation.
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Brewer J A et al. PNAS 2011;108:20254-20259

Functional Connectivity

Mindfulness meditation is also correlated with changes in connectivity between regions associated with the DMN, as meditators show different patterns of brain region co-activation compared to non-meditators. In the same study that found DMN deactivation in meditators, Brewer et al. also found that experienced meditators demonstrate increased co-activation of PCC, dorsal anterior cingulate cortex (dACC), and dorsal-lateral pre-frontal cortex (dlPFC), as well as co-activation of mPFC, insula, and temporal lobes during meditation.[7] The study also found that the change in connectivity seen in meditators is consistent in both meditation and baseline (rest) conditions, which suggests that long-term mindfulness practice may transform the experience of resting into one that is similar to a meditative state. Thus changes in functional connectivity in the DMN appears to extend beyond during meditation, and long-term mindfulness meditators may experience resting states differently than non-meditators.

Mindfulness and modes of self-reference

Coactivation of mPFC, insula,
and temporal lobes during meditation.
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Brewer J A et al. PNAS 2011;108:20254-20259

Studies in neuroimaging and functional connectivity also revealed a connection between mindfulness and different forms of self-referencing. The concept of self can be separated into two aspects: the “minimal self” referring to a “consciousness of oneself as an immediate subject of experience, unextended in time;” while the “narrative self” refers to a “coherent self (or self-image) that is constituted with a past and a future,” or one that links experiences across time.[8] The self-concept experienced during mindfulness meditation is similar to the “minimal self”, as attention is focused on immediate experience. On the other hand, the “narrative self” may be experienced when one engages in elaborative thought, rumination, remembering the past or envisioning the future, which are all related to the activities of the DMN.

Farb et al. (2007) examined the two aspects of self-concept using fMRI in participants that have received mindfulness-based stress reduction training, and novice participants that did not receive mindfulness training.[9] In this study, participants were trained to assume one of two forms of self-focus: Narrative focus (NF) calls for cognitive elaboration of mental events (much like the narrative self-concept), while experiential focus (EF) calls for the inhibition of cognitive elaboration on any one mental event and instead broadly attending to more temporally proximal sensory objects, thoughts, feelings, and sensations (similar to the minimal self-concept). It was found that in untrained novices, adopting EF is related to reduced activities in mPFC, whereas in trained participants, EF resulted in more pervasive reductions in the mPFC, and increased activities in the right lateral cortices (lateral PFC and viscerosomatic areas including the insula, secondary somatosensory cortex and inferior parietal lobule). The study proposed that the shift from midline cortices to right lateral regions indicate that mindfulness training leads to a “more self-detached and objective analysis of interoceptive (insula) and exteroceptive (somatosensory cortex) sensory events.”[9] In other words, participants who received mindfulness training are more likely to experience an objective mode of self-referencing that focuses on the present and is separate from one's own historical narrative, thus reflecting the non-elaborative thought processing component of mindfulness meditation, and the emphasis on attuning to one's present experience with an orientation of openness and acceptance. The study also proposed that increased ventral-lateral PFC activity following mindfulness training may represent change in inhibitory control, which counteracts the natural tendency towards a narrative mode of self reference (represented by activation of midline cortices in untrained participants). Thus, the midline-to-right-lateral shift may also explain the increasing cognitive inhibition[3] and decreasing DMN activity (rumination and wandering thoughts) found to be associated with mindfulness practices.

Functional connectivity in
novice and mindfulness training groups.
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Farb N A S et al. Soc Cogn Affect Neurosci 2007;2:313-322

Functional connectivity analyses performed by Farb et al. (2007) also discovered a strong co-activation pattern between the right insula and the mPFC in untrained participants that was reduced in trained participants[9]. While this may seem to contradict findings of strengthened mPFC and insular connectivity in experienced meditators[7], the decoupling of these regions is consistent with the dissociation of the two modes of self-referencing after mindfulness training. Connectivity between insula and mPFC in untrained participants[9] as well as during default mode activity[7] suggests that the two modes of self-referencing are initially integrated. With mindfulness training, one learns to identify and distinguish different cognitive and affective states, as well as physical sensations, which may lead to the decoupling of the two forms of self-awareness, and the ability to adopt one or the other at will.

State Changes

During meditation, changes in brain states can affect one's experience of cognitive, emotional, and physical sensations. These effects may be temporary, but they may also lead to more long-term or permanent changes.

EEG

EEG studies on the effects of mindfulness meditation have consistently revealed a significant increase in over all alpha and frontal theta burst activity during meditation.[10] Alpha-wave is thought to be related to internal processes such as working memory, as well as inhibition of idling or task-irrelevant cortical areas[11], thus an increase in alpha-wave activity seems to be related to the cognitive inhibition effects of mindfulness meditation, such as reducing wandering thoughts and refraining from rumination. Theta wave is associated with REM sleep, sleep/wake transition, it is also partially generated by the hippocampus[12], and may play a role in learning and memory[13]. As mindfulness meditation induce a state of calmness, it seems likely that theta burst activity would increase in a similar manner as transitioning from a wakeful state to sleep. Frontal theta EEG activity has also been negatively correlated with DMN activation[14], thus, an increase in theta burst may be related to the reduction in DMN activity associated with mindfulness meditation.[7]

In a recent study, mindfulness-based cognitive therapy (MBCT) is shown to improve attentional deficits in patients with bipolar disorder, through affecting theta wave activity. Bipolar patients initially showed significantly decreased theta band power and decreased theta/beta ratio during resting states; after receiving MBCT, frontal theta activity returned to a level comparable to healthy subjects, attentional readiness was improved, and activation of non-relevant information processing was reduced.[15]

Changes in midline cortical structures
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From "The neural substrates of mindfulness: an fMRI investigation."
By Ives-Deliperi, V. L., Solms, M., & Meintjes, E. M. 2011. 
Social Neuroscience, 6(3), 231-242.

Neuroimaging

fMRI is often used to identify the brain regions associated with mindfulness practices. In a study by Ives-Deliperi, Solms & Meintjes (2011), decreased activation was found in midline cortical structures associated with interoception (including bilateral anterior insula, left ventral ACC, right mPFC and bilateral precuneus), and significantly increased activation was found in the right posterior cingulate cortex[16].

Decrease in midline cortical structures is consistent with findings by Farb et al. (2007)[9], reflecting the role these structures play in self-referential thought. ACC is thought to be involved in attentional regulation circuits for both cognitive and emotional processing[17], as well as emotional self-control[18]. Decreased ACC activity could reflect the adopting of an open, non-judgmental orientation to experience as instructed during mindfulness practice: a mindful meditator does not try to suppress or alter emotional states, rather emotions arise and pass naturally and all attentional resources are focused on passive observation. Increased signals from right PCC may in fact suggest inhibition in the area, as research show that fMRI signal increase can indicate inhibitory activities as well as excitatory activities, since both are associated with increased metabolic demands[19]. Inhibition of PCC is consistent with findings in the DMN activity pattern[9], and considering its role in autobiographic recall[20], PCC inhibition would reflect the inhibition of elaborative processing and ruminative thoughts seen in mindfulness practices.

Trait Changes

Mindfulness meditation have also been shown to cause permanent, trait changes in the brain over long-term practice. These changes lead to long-term health benefits observed in meditators, and studies of trait changes associated with mindfulness meditation reveal clinical applications of mindfulness-based practices.

Changes in Cortical Volume

Larger gray matter volumes in meditators
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Eileen Luders , Arthur W. Toga , Natasha Lepore , Christian Gaser.
“The underlying anatomical correlates of long-term meditation:
Larger hippocampal and frontal volumes of gray matter”.
NeuroImage, Volume 45, Issue 3, 2009, 672 – 678.
http://dx.doi.org/10.1016/j.neuroimage.2008.12.061

Many studies have found a significant correlation with long-term mindfulness meditation and increases in cortical volumes. One study examined the cortical volume of meditators using voxel-based morphometry, and found greater gray matter concentrations in the right anterior insula, left inferior temporal gyrus, and right hippocampus[21]. Increased gray matter density was found in these same regions in another study, with the addition of right orbital-frontal cortex[22]. Similar increases in gray matter concentration was found in other mindfulness-based practices: participants of a mindfulness-based stress reduction program also have increased gray matter concentration, in the left hippocampus, PCC, the temporo-parietal junction, and the cerebellum.[23] Yet another study using MRI found increased cortical thickness in the prefrontal cortex and anterior insula.[24]

Changes in cortical density can have significant long-term effects. Increase in gray matter density in the prefrontal cortex and hippocampus indicate that meditation could have a strong effect on learning, memory, and plasticity. Cortical thickening may also counter act effects of cortical thinning and disruption of white and gray matters, in disorders such as epileptic seizures. Structural changes in the temporal, insular, and parietal cingulate cortices reflect the regions affected by DMN deactivation [7], distinguishing different self-referencing systems[9] and state changes caused by mindfulness meditation[16] previously discussed, and increased cortical thickness in these regions indicate that the effect of meditation is not temporary, rather it causes structural changes that may lead to long-term differences in how one experiences life.

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