meditation

Mindfulness training targets neurocognitive mechanisms of addiction (Part 2).

In the second part of this excellent review paper  (1) we look at the empirical evidence is presented suggesting that MBIs ameliorate addiction by enhancing cognitive regulation of a number of key processes.

“Mindfulness Training Ameliorates Addiction by Targeting Neurocognitive Mechanisms

Although mindfulness is an English term linked with a set of contemplative practices and principles originating in Asia over 2500 years ago, in its modern usage, mindfulness refers to a psychological phenomenon currently being studied for its relevance to mental and physical health in fields such as medicine, psychology, and neuroscience. Across these fields, a body of literature has accrued supporting the efficacy of MBIs for a range of biobehavioral disorders, including but not limited to addiction. Indeed, there is support for the effectiveness of MBIs in reducing stress and improving clinical outcomes across disorders as diverse as depression (57), irritable bowel syndrome (58), and chronic pain (59). Consequently, MBIs are increasingly well-regarded for their therapeutic promise.

MBIs are centered on practices designed to evoke the state of mindfulness, a mindset characterized by an attentive and non-judgmental metacognitive monitoring of moment-by-moment cognition, emotion, perception, and sensation without fixation on thoughts of past and future (60, 61). Thepractice of mindfulness involves two primary components: focused attention and open monitoring (61, 62). During focused attention, attention is sustained on an object while the practitioner alternately acknowledges and lets go of distracting thoughts and emotions. Objects of focused attention practice can include the sensation of breathing; the sensation of walking; interoceptive and proprioceptive feedback about the body’s internal state, movement, and position; and visual stimuli (e.g., a candle flame) (63).

Focused attention practices are often the precursor to open monitoring forms of mindfulness meditation. During open monitoring, a state of metacognitive awareness is cultivated wherein mental contents are allowed to arise unperturbed without suppression or distraction while the quality of awareness itself remains the primary focus of attention (61). This state of awareness is metacognitive in the sense that it involves monitoring the content of consciousness while reflecting back upon the process or quality of consciousness itself. In other words, the practitioner maintains awareness of the locus of attention (without trying to retain focus on a particular object) and his or her level of cognitive arousal without reacting to or elaborating on any particular content of consciousness, which, from this mental stance, are viewed as insubstantial and ephemeral. Putatively, focused attention and open monitoring emphasize or differentially activate different cognitive capacities during the mindful state, including attentional vigilance, attentional re-orienting, executive monitoring of working memory, response inhibition, and emotion regulation (62). As such, they are often combined during a single practice session, which typically commences with focused attention and then evolves toward a more open monitoring approach.

Engaging in these practices repeatedly over time may induce neural and cognitive plasticity (7); recurrent activation of the mindful state during meditation may leave lasting neurobiological traces that accrue into durable changes in the dispositional propensity to be mindful in everyday life even while not meditating (64). In that regard, MBIs can produce significant increases in dispositional mindfulness that mediate the effects of mindfulness training on clinical outcomes (65). Germane to the current discussion of neurocognition in addiction, dispositional mindfulness is significantly inversely associated with addiction attentional bias (1) and craving (66), positively associated with autonomic recovery from stress and substance cue-exposure (67), and correlated with various indices of cognitive control (6870). MBI-related increases in dispositional mindfulness might be mediated through neuroplasticity stimulated by experience-dependent alterations in gene expression (71, 72). Indeed, cross-sectional studies have demonstrated significant differences in gray matter volume between meditation practitioners and meditation-naïve controls, particularly in regions of PFC that instantiate cognitive control (e.g., inferior frontal gyri) and higher-order associative processing (e.g., hippocampus) (7377). Moreover, longitudinal research has shown that participants in an 8-week MBI evidenced increased gray matter density in posterior cingulate cortex, temporo-parietal junction, and cerebellum, compared to controls (78), and reduced amygdala volume that correlated with the degree of stress-reduction achieved from mindfulness training (79).

Through focused attention and open monitoring forms of meditation, MBIs exercise a number of neurocognitive processes believed to go awry in addiction. Indeed, MBIs may be fruitfully conceptualized as means of training or exercising prefrontally mediated cognitive control networks which have become atrophied or usurped in the service of drug seeking and use. By strengthening PFC functions and the ability of the PFC to modulate other brain networks in a context-dependent manner, MBIs may provide the global benefit of enhancing neurocognitive flexibility – augmenting a “domain-general” resource that may then be applied across the manifold subcomponent processes implicated in psychological health (e.g., cognitive regulation of automaticity, attention, appraisal, emotion, urges, stress reactivity, reward processing, and extinction learning). These processes do not operate in isolation; they are linked in mutually interdependent, interpenetrating, recursive networks [for reviews, see Ref. (2, 3)]. MBIs may restructure dysregulated processes by strengthening functional connectivity and efficiency of prefrontally mediated self-regulatory circuits (see Figure 2). Below, we propose a number of hypothetical neurocognitive targets that could mediate the therapeutic effect of MBIs on addictive behavior.

FIGURE 2
 
 

Figure 2. Mindfulness-centered regulation: the central tenet of this model posits that mindfulness-based interventions (MBI’s) may remediate dysregulated habit behaviors, craving, and affect primarily by way of strengthening functional connectivity: (1) within a metacognitive attentional control network (PFC, ACC, Parietal); and (2) between that metacognitive attentional control network and the (a) habit circuit, (b) craving circuit, and (c) affect circuit.

Habit Responses

Substance dependent individuals typically experience euphoria during initial stages of drug-use. Yet, as experience with the drug increases, the reward associated with drug-taking becomes dramatically attenuated. Despite diminishing returns in positive emotional experiences resulting from substance use, dependent users continue to use their drug of addiction. Undergirded by neuroplastic changes in striatal circuitry, habitual drug-use becomes an overlearned process that can become automatized (12, 80).

Relatedly, human positron emission tomography (PET) research has found that meditation practice increases dopamine release in the ventral striatum (81). This pioneering study by Kjaer et al. (81) suggests that MBIs may target striatal-dopamine transmission – a neural function believed to mediate automaticity that becomes dysregulated following chronic drug-use. Though more investigation is needed to elucidate effects of mindfulness on brain-behavior relations subserving drug-use action schemas, early research on the effects of mindfulness on behavioral measures of automaticity has emerged [e.g., Ref. (82)]. Such research provides a theoretical foundation for the potential efficacy of MBIs for interrupting drug-use action schemas. Hypothetically, mindfulness training may increase awareness of the activation of drug-use action schemas when triggered by substance-related cues or negative emotion, thereby allowing for the disruption of automatized appetitive processes with a controlled coping response. As posited in our model of mindfulness-centered regulation (Figure 2), mindfulness training may enhance functional connectivity in a cortico-thalamic loop including prefrontal, cingulate, parietal, and dorsal thalamus nodes, strengthening an executive regulatory circuit providing feedback to the striatum and medial temporal lobe. This feedback process is theorized to allow for greater consciousness of thoughts and behaviors that were previously enacted with little conscious awareness.

The practice of mindfulness in daily life is focused on developing awareness of automatic behavior. Indeed, many MBIs prescribe informal mindfulness practices where individuals are instructed to engage in everyday, repetitive tasks (e.g., washing the dishes) with full consciousness of the sensorimotor aspects of the activity. Such informal mindfulness practices are designed to reduce mind-wandering and strengthen conscious control over automaticity. Potentially as a result of such practices, mindfulness training has been shown to decrease habit behavior (83) and reduce rigid adherence to scripted cognitive responses (82). These findings accord with early theoretical accounts which conceptualized mindfulness meditation as a form of “deautomatization,” whereby patterns of motor and perceptual responses which had been rendered automatic and unconscious through repetition are reinvested with conscious attention (84). Thus, is plausible that mindfulness training may deautomatize habitual addictive responses through both formal meditations focused on regulating automatic appetitive impulses as well as informal mindfulness practices designed to increase generalized awareness of automaticity. In light of findings suggesting that conscious cognitive control disrupts automatic processing (20, 8587), mindfulness training may interrupt drug-use action schemas by augmenting top-down control via a frontoparietal metacognitive attention network, facilitating the strategic deployment of self-regulatory processes to reduce or prevent substance use. The effects of mindfulness training on inhibition of habit responses might be indexed with performance on an Emotional GoNoGo task (88), where subjects would be asked to withhold automatized “go” responses in the context of emotional interference from a drug-related (i.e., a drug-related background image) or negative affective stimulus (i.e., an aversive background image).

Attentional Bias

Given that drug-use action schemas may be evoked by cues associated with past substance use episodes, activation of addictive habits may be interrupted by re-orienting attention from substance-related stimuli to neutral or salutary objects and events. MBIs may be especially efficacious in that regard. Focused attention and open monitoring mindfulness practices capitalize on attentional orienting, alerting, and conflict monitoring – the fundamental components of attentional control (89, 90). Consequently, studies indicate that mindfulness is linked with enhanced attention regulation (61, 91). For instance, mindfulness training is associated with strengthening of functional connectivity within a dorsal attentional network (92) and MBIs can increase attentional re-orienting capacity, i.e., the ability to engage, disengage, and shift attention efficiently from one object to another subserved by dorsal attentional systems (93, 94). Other studies demonstrate that long-term mindfulness training strengthens alerting (93, 95), i.e., a vigilant preparedness to detect and attend to incoming stimuli, subserved by the ventral attentional stream. In addition, dispositional mindfulness is positively associated with self-reported attentional control (68) and behavioral indices of sustained attention capacity (70). Recently, data from a randomized controlled trial indicated that 8 weeks of Mindfulness-Oriented Recovery Enhancement led to significant reductions in attentional bias to pain-related cues in a sample of opioid-misusing chronic pain patients (96).

MBIs may target addiction attentional bias by facilitating attentional disengagement from substance-related stimuli. In support of this hypothesis, a study of alcohol dependent adults in residential treatment identified a significant negative correlation between dispositional mindfulness and alcohol attentional bias for stimuli presented for 2000 ms that remained robust even after controlling for alcohol dependence severity, craving, and perceived stress (1). Hypothetically, alcohol dependent persons higher in dispositional mindfulness might exhibit increased capacity for attentional disengagement from alcohol cues by virtue of enhanced PFC and anterior cingulate cortex functionality, as these brain structures have been implicated in addiction attentional bias (9799). Concomitantly, the degree to which alcohol dependent individuals higher in dispositional mindfulness were better able to disengage their attention from alcohol cues than their less mindful counterparts predicted the extent of heart-rate variability (HRV) recovery (an index of prefrontal-autonomic regulation) from stress-primed alcohol cue-exposure (67). Mindfulness training may also affect attentional orienting to substance-related cues. Among a sample of alcohol dependent adults in inpatient treatment, Mindfulness-Oriented Recovery Enhancement was found to result in significant effects on alcohol attentional bias for cues presented for 200 ms (7), indicating modulation of automatic initial orienting to alcohol cues [c.f. (23)]. In individual difference analyses, reductions in attentional bias following Mindfulness-Oriented Recovery Enhancement were significantly associated with decreases in thought suppression, which were, in turn, correlated with increases in HRV recovery from alcohol cue-exposure and improvements in self-reported ability to regulate alcohol urges.

Hence, mindfulness training may strengthen the capacity to regulate attention in the face of conditioned stimuli associated with past substance use, countering attentional biases by refocusing attention on neutral or health-promoting stimuli (e.g., the sensation of one’s own breath or a beautiful sunset). Repeatedly redirecting attention from substance-related cues toward innocuous stimuli may foster extinction of associations between substance-related cues and drug-use action schema. This potential mechanism may explain how attentional bias modification among addicts leads to decreased substance use and improved treatment outcomes (100, 101). Future research could evaluate the effects of mindfulness training and MBIs on addiction attentional bias with the use of a dot probe task alone or coupled with eye tracking and analysis of event-related potentials (ERPs) to determine at what stage of attentional selection (initial orienting vs. later attentional disengagement) training has significant effects.

Cue-Elicited Craving

The urge to seek intoxication from addictive substances is driven, in part, by reactivity to substance-related stimuli which have been conferred incentive salience, and is magnified by negative affective states. Several studies demonstrate that MBIs can produce significant reductions in craving (4, 8,102105). However, other studies have failed to identify significant reductions in craving among participants of MBIs (7, 106108).

Mindfulness-based interventions may positively influence craving-related processes in several ways. First, mindfulness training may decrease bottom-up reactivity to drug-related stimuli, as mediated by reduced activation in the subgenual anterior cingulate cortex and striatum during exposure to substance cues (105). Second, mindfulness training may decouple negative emotion from craving. Although negative emotion is a common precipitant of craving and subsequent relapse (109), mindfulness training may extinguish this association, such that an addict experiencing sadness, fear, or anger could allow these emotions to arise and pass without triggering an appetitive reaction. Indeed, substance dependent individuals participating in Mindfulness-Based Relapse Prevention were less likely to experience craving in response to depressed mood, and this reduced craving and reactivity to negative emotion predicted fewer days of substance use (110).

MBIs may also produce therapeutic effects by increasing awareness of implicit craving responses. Tiffany (20) proposed that conscious craving occurs when an activated drug-use action schema is blocked from obtaining the goal of drug consumption. As such, persons in acute withdrawal, persons unable to obtain drugs (e.g., due to lack of funds or availability), or persons attempting to maintain abstinence in the face of triggers may experience an upwelling of craving for substances. In contrast, according to this theory, addicts who are able to obtain and use drugs in an unimpeded fashion would not experience craving. Similarly, persons in long-term residential treatment who are isolated from drug-related cues are unlikely to be conscious of craving. Without awareness of craving, the addict may unwittingly remain in high-risk situations and thus be especially subject to relapse. Indeed, lack of awareness of substance craving has been shown to be predictive of future relapse (111). MBIs may increase conscious access to the appetitive drive to use substances by virtue of their effects on increasing interoceptive awareness (78, 112). In that regard, mindfulness training has been shown to increase activity in the anterior insula during provocations by emotionally salient stimuli (113, 114). The anterior insula subserves interoception and awareness of the physical condition of the body, among other related processes (115). Increased neural activity in the insula during mindfulness meditation may index heightened access to interoceptive information.

In synthesizing the findings regarding attentional bias and cue-induced craving, we suggest that MBIs may restructure attentional bias away from drug-related reinforcing stimuli (e.g., drug-cues, negative affective stimuli) and facilitate the addict’s attempts to deal with associated cravings. We posit that mindfulness-centered regulation of cue-elicited appetitive responses occurs as a result of strengthening frontal-executive circuit-function and enhancing neural communication to the hippocampus and thalamus through formal and informal mindfulness meditation practices. The hippocampus is critical for context-dependent learning and memory – with reciprocal connectivity to brain regions that code for reward (ventral striatum), interoception (insula), affect (amygdala), and thalamus. In turn, the thalamus, a complex structure that is generally considered to serve as a relay station between limbic, striatal, and cortical circuits, contains efferent and afferent projections with striatal, limbic, somatosensory, ACC, lateral and medial PFC, and OFC. Thus, the recovering addict may utilize mindfulness training to become aware of which cues are under the spotlight of attention, and become more sensitive to how those cues may trigger changes in body state and motivation drive.

Hence, mindfulness may increase awareness of craving and thereby facilitate cognitive control of otherwise automatic appetitive impulses. In that regard, a recent study found that participation in Mindfulness-Oriented Recovery Enhancement was associated with decreased correlation strength between opioid craving and opioid misuse, suggesting that mindfulness training may have decoupled appetitive responses from addictive behaviors (8). This mechanism may explain the disparate findings vis-a-vis the effects of mindfulness on craving: because of potential underreporting of baseline levels of craving among individuals with impaired insight into their addiction (34), this increased awareness may confound researchers’ attempts to measure the impact of mindfulness training on craving, resulting in an apparent lack of change in craving over time.

The effects of mindfulness on cognitive regulation of craving might be measured by utilizing neuroimaging methodology (e.g., fMRI) to investigate neural circuitry function while participants attempt to regulate their craving response to salient drug-cues. For example, cognitive regulation appears to decrease cigarette craving concomitant with increased activity in dACC (116) and prefrontal regions coupled with attenuated activity in striatal regions (117). A complementary approach to probing the effects of mindfulness on regulating craving may be to utilize real-time fMRI (rt-fMRI). rt-FMRI involves providing subjects with real-time feedback of the BOLD signal within a brain region of interest (ROI) while they attempt to regulate the response within that ROI. This approach has been used to manage pain (118) and reduce cigarette cue craving in nicotine dependent smokers during smoking cessation (119). Evaluating the effects of mindfulness-centered regulation of craving-related neural circuitry in real-time may include a number of benefits including: (a) directly measuring which circuits are being effectively modulated and which are not; (b) feedback to the subject that will help guide mindfulness efforts; and (c) identifying individual differences associated with differential effects of MBIs on specific neural mechanisms.

Cognitive Appraisal

Insofar as stress evokes automatic responses and impairs prefrontally mediated cognitive control functions (120), exposure to socioenvironmental stressors may render addicts in recovery vulnerable to relapse (1, 22, 121). Mindfulness training may allay stress-induced relapse by virtue of its stress-reductive effects (122). Although early theorists believed that mindfulness meditation reduced stress primarily by evoking a generalized relaxation response (123), modern research indicates that mindfulness practice may also attenuate stress by targeting cognitive mechanisms (1, 124). One potential target of mindfulness is cognitive appraisal, the process whereby stimuli and their environmental context are evaluated for their significance to the self (125). Appraisals of threat or harm elicit negative emotional reactions coupled with activation of stress physiology. When recurrent, such emotional reactivity biases perception, leading to exaggerated, overestimated appraisals of threat and underestimations of self-efficacy (126), and ultimately, sensitization to future stressors (127).

In contrast, mindfulness, which has been conceptualized as a non-reactive form of awareness (128) may enable the individual to cognitively appraise his or her present circumstances with less emotional bias, and to more accurately assess his or her ability to cope with present challenges (60). Thus, MBIs may impact both primary (rapid and implicit) and secondary (slow and explicit) appraisal processes (125). In partial support of this hypothesis, a recent neuroimaging study revealed that, in contrast to a meditation-naive control group, mindfulness meditation practitioners exhibited decreased reactivity to briefly presented negative emotional cues in frontal-executive brain regions (i.e., dorsolateral PFC) and less deterioration of positive affect in response to cue-elicited amygdala activation (31). These data suggest that mindfulness training may alter the allocation of cognitive resources during appraisal of negative emotional stimuli and attenuate the influence of limbic reactivity on mood state. Other research demonstrates that mindfulness training minimizes emotional interference from unpleasant stimuli [e.g., Ref. (129)]. In so doing, mindfulness training may reduce biases toward negative emotional information processing. Among persons with a history of depression, Mindfulness-Based Cognitive Therapy reduces overgeneral memories (130) and cognitive bias toward negative information (131). Among individuals suffering from chronic pain, Mindfulness-Oriented Recovery Enhancement decreases cognitive bias toward pain-related cues (96). Together, these findings suggest that MBIs may decrease negative emotional bias in initial cognitive appraisal processes, thereby reducing the downstream effects of stress on addictive behavior. As mindfulness-centered regulation enhances cortico-thalamic-limbic functional connectivity, the recovering addict becomes more aware of relations between attention, emotional state, and motivation. This awareness provides an opportunity to deploy cognitive strategies to respond to the environment in a more adaptable context-dependent manner, rather than responding from a pattern of overlearned reactive behaviors.

One approach to evaluating the effects of mindfulness-centered regulation of stress appraisal may be to utilize fMRI paradigms like the affective Stroop task to probe cognition-emotion interactions (31). If mindfulness reduces stress appraisals, aversive stimuli may produce less emotional interference during cognitive task performance, resulting in reduced reaction time decrements and decreased activity in prefrontal-limbic circuitry on trials following aversive cues. Alternatively, phasic cortisol output and sympathetic nervous system reactivity could be measured during laboratory stress induction techniques such as the Trier Social Stress Test (132) and correlated with self-reported appraisals of stress versus challenge during the task both pre- and post-mindfulness training.

I will be critiquing this excellent hypothetical model in future blogs.

Although I agree with most points made, I also disagree with certain points and will be addressing what I perceive as limitations in this model.

The point is that in recent blogs I have posted articles offering hypothesis on how meditation helps change the addicted brain via meditation based neuroplasticity and in areas of the brain that are impaired and which contributed to the neuro-cognitive mechanisms of addiction and this is the good news for all people hoping to recover from addiction by recovering essential brain function and connectivity.

It does work if you work it!

References

1. Garland, E. L., Froeliger, B., & Howard, M. O. (2013). Mindfulness  training targets neurocognitive mechanisms of addiction at the attention-appraisal-emotion interface. Frontiers in psychiatry, 4.

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