Here we conclude our two part blog on possible brain mechanisms which may be altered via the practice of mindfulness meditation.

We will be adding more on the role of  meditation in the next few blogs as it does appear to have great utility in treating addictive behaviours.

Neurobiology of Mindfulness Meditation

Our review focuses specifically on mindfulness meditation as it is incorporated into MBRP, based on practices from the Vipassana tradition, and largely based on the related treatments of MBSR (Kabat-Zinn, 1990) and MBCT (Segal, et al., 2002). We focus our review on studies that have focused on either brain structure or functional changes in response to mindfulness practice. For a general discussion on the mechanisms of mindfulness meditation, we direct the reader to a recent review by Hölzel and colleagues (2011a).

Brain structure

Ott, Hölzel, and Vaitl (2011) provided a narrative review of five recent morphometric studies that compared experienced meditators with control groups of non-meditators, with three of the studies examining the brain structure of experienced practitioners of Vipassana (Hölzel et al., 2008; Luders et al., 2009) and insight meditation (Lazar et al., 2005). Lazar and colleagues (2005) found greater cortical thickness in the right anterior insula and the PFC of highly experienced insight meditation practitioners (average 9 years of practice) in comparison to control participants without meditation…

Importantly, the study did not find significant differences in mean thickness across the entire cortex, suggesting that meditators had greater cortical thickness in specific regions (e.g., insula, PFC). While the methods employed in this study are anatomical in nature, Lazar and colleagues (2005) suggest that greater cortical thickness in the insula may be relevant to bottom-up interoception including awareness of bodily sensations and emotions (and as part of the putative emotional salience network with the ACC), while increased cortical thickness in the prefrontal cortex is likely related to top-down executive control.

Hölzel and colleagues (2008) identified greater gray matter concentration in the right anterior insula among experienced meditators in comparison to non-meditators. Additionally, VBM identified greater gray matter concentration in the left inferior temporal gyrus, and the right hippocampus among experienced meditators in comparison to non-meditators…

Luders and colleagues (2009) found greater gray matter volume in the left inferior temporal gyrus and in the right hippocampus among 22 experienced meditators with an average of 24.18 years of meditation (range = 5 to 46 years) in comparison to 22 non-meditators, who were matched for age and gender.

The right orbitofrontal cortex (OFC) also revealed greater volume in meditators compared to non-meditators, which is noteworthy given the top-down roles of the OFC in appraisal of emotional stimuli and behavioral inhibition. The authors concluded that greater volume in the right OFC might “allow disengagement from automatic thoughts and habits, and therefore permit consideration of options that would be more congruent with needs and values” (p. 676;Luders et al., 2009).

Consistent with this idea that more years of practice are associated with greater volume differences  Hölzel et al. (2008) found that gray matter concentration in the left inferior temporal gyrus, the right insula, and the medial OFC was correlated with hours of meditation practice.

Brain function

Over the past 10 years, there has been a steady increase in functional brain imaging research on experienced meditation practitioners, meditative states, and the effects of meditation training on brain functioning in novice meditators. Results from the majority of studies suggest that meditation experience and meditation practice are associated with different functional responses to environmental stimuli, pain, emotional responding, and present-moment versus self-focused attention (e.g., Farb et al., 2010; Orme-Johnson, Schneider, Son, Nidich, & Cho, 2006; Taylor et al., 2011).

One of the earliest functional imaging studies compared self-selected Vipassana meditators (average 8 years of practice) with non-meditators matched for sex, age, education, and handedness (Hölzel et al., 2007). The effect of a one-minute breath awareness exercise on the BOLD signal was assessed with fMRI. Results revealed stronger activity in the medial PFC (mPFC) and the most rostral aspect of the anterior cingulate cortex (rACC) during meditation in meditators compared to non-meditators. Given the roles of the mPFC and the rACC in emotional processing and regulation, the observed pattern of activation suggests that meditation may contribute to more cortical processing of emotion and potential top-down emotion regulation.

More recent research suggests that mindfulness meditation contributes to subcortical processing of emotion as well. For example, Taylor and colleagues (2011) found that mindfulness practice was associated with deactivation of the left amygdala while viewing either positive or negative emotional stimuli among a group of individuals who practiced meditation for a week prior to the study, whereas experienced meditators did not show such deactivation. Both the inexperienced and experienced meditators rated the emotional stimuli as less intense during mindfulness practice, suggesting that mindfulness may be associated with improved bottom-up emotion regulation…

Functional connectivity studies have also identified numerous differences among experienced meditators in comparison to non-meditators or individuals who recently began training in meditation…

Imaging research has also begun to illuminate differences in circuit activation by demonstrating either coupling (i.e., simultaneous activation) or decoupling (i.e., disconnected activation) of associated brain regions (e.g., attentional networks, the emotional salience monitoring network, anterior cingulate and medial frontal cortices) after one month of meditation training (Xue, Tang, & Posner, 2011) and among experienced meditators (Brewer, Worhunsky, Gray, Tang, Weber, & Kober, 2011; Hasenkamp & Barsalou, 2012; Hölzel et al., 2007). Farb and colleagues (2007) found that experiential focused meditation (i.e., focus on current experience without attaching meaning), in comparison to a narrative focus (i.e., cognitive elaboration of thoughts), was associated with a decoupling of the right insula and mPFC with a shift toward greater activity in the dlPFC among individuals who attended an 8-week course in meditation. In contrast, non-meditators evinced a strong coupling of the insula with the mPFC (Farb et al., 2007).

The authors concluded that the uncoupling of the mPFC among meditators reflects a tendency toward self-detachment from interoceptive cues, while the increased BOLD signal in the dlPFC may represent enhanced present moment awareness. The greater recruitment of dlPFC in meditators is noteworthy given the roles of this region in top-down emotion regulation processes (Lieberman et al., 2007).

Studies on functional connectivity have found altered connectivity between meditators and non-meditators during a “resting state,” suggesting that connectivity changes are maintained outside of meditative states (Brewer et al., 2011; Hasenkamp & Barsalou, 2012; Xue et al., 2011). As such, MBRP may help individuals detach from craving and, at the same time, experience greater dlPFC functioning with concomitant enhanced present moment awareness and improved top-down emotion regulation.

At the center of the practices from numerous meditation traditions, and at the heart of MBRP, is a focus on present moment awareness. This often involves shifting one’s attention away from internal dialogue and rumination to sensory experiences in the present moment.

A recent study by Hasenkamp and colleagues (2012) examined neural activity using fMRI during fluctuating cognitive states of a proposed cognitive cycle that was defined by mind wandering, awareness of the mind wandering, shifting attention, and sustained attention.

In this paradigm meditation on the breath was the intended task and the target of sustained attention. Experienced meditators were instructed to pay attention to their breath while in the scanner, and to press a button when they became aware of their mind wandering.

When participants indicated awareness of mind wandering, there were robust activations in the anterior insula and dorsal ACC.

The anterior insula and dorsal ACC were highly correlated, suggesting neural integration. This integration has been associated with various top-down and bottom-up processes including emotional awareness, goal directed behavior, cognitive-control (including conflict monitoring and error detection), self-regulation, and the detection of salient external and internal events (Craig, 2009; Seeley et al., 2007). These findings, in conjunction with those of Farb and colleagues (2007), who found a decoupling of the insula with the mPFC and heightened BOLD signal in the dlPFC during meditation, provide evidence of specific activation patterns within the prefrontal and insula/ACC circuitry that may reflect present moment awareness. Given that a primary focus of MBRP is increasing present moment awareness, it follows that those who practice MBRP might evince changes in the PFC and insula/ACC circuitry that corresponds with their level of present moment awareness.

Hypothesized Mechanisms of Neurobiological Change During and Following MBRP

Hypothesized functional changes

Changes in the insula and hippocampus as observed in the studies cited here suggested that such activation due to mindfulness meditation may cause a shift from recall processing of past associations that may be “viscerally embedded” within insular circuitry to present moment awareness and experiential processing. Concomitant activity in the ACC and PFC could allow one to filter incoming information and inhibit inappropriate emotional or behavioral responses. To the extent that mindfulness training may improve functional connectivity of the ACC with the PFC (Xue et al., 2011), as well as improve top-down cognitive control of emotions and greater coupling of the insula with the dlPFC (Farb et al., 2007), it follows that individuals who receive MBRP may be more likely to exhibit greater top-down cognitive and inhibitory control.

As noted by Goldstein and colleagues (2009), “interventions to strengthen ACC activity or interconnectivity may be beneficial to enhancing top-down monitoring and emotion regulation as a strategy to reduce impulsive and compulsive behavior in addiction” (p. 9453).

…the skills taught in MBRP stand in stark contrast to avoidance, thought suppression, and distraction of CBT. Given recent evidence that mindfulness may be more effective than thought suppression or distraction in reducing negative affect (Huffziger & Kuehner, 2009; Rogojanski, Vettese, & Antony, 2011) and substance use (Bowen & Marlatt, 2009), we expect MBRP would exert stronger top-down neural regulation over the craving circuit with more varied neural responses possibly in the ACC/insular emotional saliency circuitry in response to a craving regulation task during imaging than those exhibited by participants in the Volkow and colleagues (2010) study.

 It has been hypothesized that lack of self-awareness during experiences of negative affect and craving may increase vulnerability to relapse (Goldstein et al., 2010). Further, it is proposed that mindfulness practices might help prevent relapse by increasing self-awareness (e.g., Jang et al., 2010) and acting with awareness (Bowen et al., 2009), and by reducing reactivity to drug cues (e.g., Garland, Gaylor, Boettiger, & Howard, 2010) and negative affective states (e.g., Witkiewitz & Bowen, 2010).

Changes to the insula and the connectivity between the insula and frontal cortical networks (including the ACC) during meditation training could contribute to both the increases in awareness and the reductions in the subjective experiences of craving reported by individuals following MBRP. Further, if participation in MBRP increases gray matter volume in the PFC (e.g, Lazar et al., 2005), then the ability to disengage from the experience of craving as an automatic response to drug cues and related stimuli (e.g., negative moods) might allow individuals to make choices that are more congruent with maintaining treatment gains.

The extent to which mindfulness practice in MBRP decreases automatic responses to craving cues and negative affect may be reflected in part in hemodynamic responses to stress. In preliminary analyses of an ongoing MBRP study, we found significantly less heart rate reactivity and increased high-frequency heart rate variability (HF-HRV), a measure of cardiac vagal control and an indicator of self-regulation (Thayer & Lane, 2009), in response to a laboratory stressor among those treated with MBRP compared to those in treatment as usual (unpublished data). Increases in phasic HF-HRV during stress has been observed with mindfulness and is interpreted as a more adaptive, self-regulatory response to stress (e.g., Ditto, Eclache, & Goldman, 2006;Tang, et al., 2007). Thus, while the HRV data reveal that from the bottom-up there is a shift to a more favorable (less reactive) stress response in the MBRP group, the concomitant increase in HF-HRV suggests top-down processes are also being recruited to manage the stress response post-MBRP (see Thayer & Lane, 2000).

To summarize…brain plasticity in response to mindfulness practices may positively affect brain recovery with functional benefits that may reverse, repair, or compensate for detrimental neuroadaptive changes brought on by addiction.

Based on our review of relevant studies, as well as our own clinical research…suggests that mindfulness practice influences bottom-up responding, particularly by reducing responsivity to stressors (unpublished data; Brewer et al., 2009) and by decreasing bottom-up reactivity to craving cues (Westbrook et al., in press). Changes in the stress response system, the emotional salience monitoring system (including insula/ACC circuitry and the amygdala), and automaticity of drug-seeking behavior (involving the striatum) may all contribute to changes in bottom-up responding following MBRP. Behavioral interventions for substance use disorders and mindfulness practices are associated with top-down changes in executive functioning, cognitive control, attention regulation, and emotion regulation (see reviews by Hölzel et al., 2011a; Potenza et al., 2011). Changes in inhibitory control, conflict monitoring, motivation, and decision making via the dlPFC, ventromedial PFC, OFC, hippocampus, ACC, and insula may all contribute to the changes in top-down monitoring following MBRP.

References

Witkiewitz, K., Lustyk, M. K. B., & Bowen, S. (2013). Retraining the addicted brain: A review of hypothesized neurobiological mechanisms of mindfulness-based relapse prevention. Psychology of Addictive Behaviors, 27(2), 351.