The role of mindfulness meditation as a therapeutic health care modality is becoming established in the medical literature and in military hospitals. Advances in the medical standard of care have encouraged the use of meditation and other mind-body practices for the treatment of pain (Wells, Smitherman, Seng, Houle, & Loder, 2014), depression (Srivastava, Talukdar, & Lahan, 2011), anxiety (Hart, 2013), posttraumatic stress disorder (PTSD) (Kim, Schneider, Kravitz, Mermier, & Burge, 2013), and numerous other mental health care concerns (Joy, 2014). Mindfulness practices are taught widely throughout the Department of Veterans Affairs, including many Veterans Affairs medical centers, and recent research is beginning to evaluate the clinical benefits of these mindfulness programs (Nassif et al., 2015). In addition to providing clinical health benefits, mindfulness practices are also identified as helping to overcome stress and improve quality of life, sleep quality, cognitive performance, and many other enhancements in physical and psychological function. Furthermore, perhaps as a result of the health-regulating effects of meditation practices, evidence supports the possibility that mindfulness may be one of the trait characteristics mediating resilience and the capacity to adaptively overcome stress and/or other life traumas.
If mindfulness can be shown to mediate resilience, and the neurobehavioral mechanisms of action can be identified, then perhaps specific behavioral elements of the practice can be identified and targeted to both prevent and treat mental health problems in the military. Several studies have already begun to explore the impact of mindfulness training on resiliency in military forces, and programs are currently being implemented on the basis of the assumption that meditation may enhance resiliency traits. Indeed, mindfulness practices have been a component of martial arts training for thousands of years to improve military performance. This chapter will explore the ancient wisdom of mindfulness practices as way to bulletproof the psyche of our armed forces from the perspective of modern, evidence-based scientific research.
Resilience is broadly defined as the ability to bounce back from adversity (Ledesma, 2014; Southwick, Bonanno, Masten, Panter-Brick, & Yehuda, 2014) and more specifically as growth after disruption (Richardson, 2002). Key elements of such growth involve an element of introspection and an opportunity for change. Introspection and transformation are also recognized as defining elements of mindfulness meditation (Fox et al., 2012), suggesting that there may be a relationship between the practice of meditation and the trait of resilience. Werner and Smith (2001) similarly identified resilient individuals as those having an “internal locus of control” and “a more positive self-concept,” which are also defining characteristics of those who practice mindfulness meditation (Crescentini & Capurso, 2015).
Both resilience and mindfulness are also defined by their association with stress. The ability to maintain biochemical balance without stress activation is referred to as homeostasis. The stress response occurs when there is a real or perceived threat to homeostasis. Stress activation of the hypothalamic-pituitary-adrenal (HPA) axis involves a cascade of hormonal changes that correspond with a heightened state of arousal. The dynamic process by which the body is able to respond to stress activation of the HPA axis and return to a biochemically balanced state is referred to allostasis. Researchers have defined “resilience” as either the ability to maintain homeostasis following an experience of stress or enhanced allostasis (Alim et al., 2012).
Mindfulness mediates the stress response in two ways. Greater indices of mindfulness are associated with (1) lower levels of response to typical stressors (maintaining homeostasis) and (2) a more rapid return to the relaxed state when stress is activated (improved allostasis; Herman et al., 2016). Resilience is also associated with both lower levels of response to typical stressors and the ability to bounce back to a normal state after stress activation (Sinha, Lacadie, Constable, & Seo, 2016). Resilient individuals are more likely to maintain homeostasis and, when disrupted by stress, have a faster rate of allostasis to normal function. Studies exploring the role of training in mindfulness meditation as a way to improve resilience in the military suggest that mindfulness training may indeed enhance resilience in the armed forces (Johnson et al., 2014). Studies of the physiological basis of mindfulness and resilience show that the underlying brain mechanisms that are altered by mindfulness training provide a physiological foundation that characterizes emotional resilience (Haase et al., 2016).
Researchers have sought to identify a number of physiological mechanisms that may underlie characteristics of resiliency. These physiological foundations of resilience are located in the brain and include changes in both brain neurochemistry and neural structures (Feder, Nestler, & Charney, 2009). Mindfulness exercises have also been identified that are associated with these same neurochemical and structural characteristics by which we identify resiliency.
In a review by Charney (2004), 11 biochemical correlates that may underlie resiliency and vulnerability were identified to mediate the psychobiological response to extreme stress. These biochemicals associated with stress and resiliency include the hormones cortisol, dehydroepiandrosterone (DHEA), corticotrophin-releasing hormone (CRH), testosterone, and estrogen; neurotransmitters (neurohormones) of norepinephrine, dopamine, serotonin, and gamma-aminobutyric acid (GABA; benzodiazepine receptor reactivity); and neuropeptides Y (NPY) and galanin.
Cortisol, DHEA, and CRH are normal parts of the HPA activation that characterize the stress response. A study of soldiers performing the U.S. Army Survival Course found that those who completed the training had dramatically increased cortisol levels and that these levels of cortisol did not return to normal baseline levels following a period of recovery (Morgan et al., 2001).
Numerous studies on the mechanism of action of mindfulness practices have found that meditation is associated with a rebalancing of essential hormones and in particular can rebalance those hormones associated with the stress response, PTSD, and resiliency. For example, following a mindfulness meditation intervention, resilient medical students had lower levels of cortisol, DHEA, and CRH reaction relative to baseline than nonresilient cohorts (Turakitwanakan, Mekseepralard, & Busarakumtragul, 2013). Resilient subjects also returned more quickly to homeostatic levels of these hormones after a stress-eliciting event. Just as research has shown that resilience is defined as the ability to maintain lower levels of cortisol, DHEA, and CRH in the face of stressors, mindfulness exercises are proving to be a behavioral intervention that controls cortisol, DHEA, and CRH levels (Matousek, Dobkin, & Pruessner, 2010). The more practice one has in mindfulness meditation, the lower the increase in cortisol and CRH in response to stressful events, improving the ability to return to homeostasis following a stress or trauma that activates the HPA axis (Castro et al., 2012). Again, mindfulness exercises have been found to hasten the return to equilibrium following activation of the HPA axis and release of cortisol, DHEA, and CRH (Carlson, Speca, Patel, & Goodey, 2004). These data suggest that mindfulness practices can enable self-regulation of neurohormonal balance and that this neurohormonal balance is the foundation of the behavioral state we are defining as resilience.
The stressful experience of Army survival testing was also found to significantly decrease testosterone (Morgan et al., 2001). Low levels of testosterone are associated with depression, PTSD, and other indices of declining mental health (Yeap, 2014). Resilience, however, is defined by higher levels of testosterone, which in turn is related to higher social rank, competitive success, and greater feelings of personal success and connectedness within social groups (Russo, Murrough, Han, Charney, & Nestler, 2012).
Similarly, estrogen levels are also recognized as a relevant determinant of resilience. A study by Bredemann and McMahon (2014) found that animals pretreated with estrogen (17β estradiol) before being exposed to inescapable shock were less likely to exhibit symptoms of learned helplessness during the shock. Learned helplessness is associated with, and used as a model of, depression (Seligman, 1972). Furthermore, treatment with estrogen was able to reverse previously established learned helplessness behaviors. These findings suggest that homeostatic levels of estrogen may play a protective role in preventing depression and that balancing levels of estrogen may be associated with resilience (Bredemann & McMahon, 2014).
Meditation practices may also provide a prophylactic effect on stress- induced disruptions in testosterone and estrogen, serving as a behavioral intervention for rebalancing of these critical hormones associated with resiliency. Given that mindfulness practices modulate the biomarkers associated with stress (Carlson et al., 2004; Matousek et al., 2010; Walker, Pfingst, Carnevali, Sgoifo, & Nalivaiko, 2017), and stress affects levels of testosterone and estrogen, meditation may also impact the hormonal mechanisms that are fundamental to resilience.
Changes in neurotransmitter systems also appear to mediate the relation between mindfulness practices and resiliency. Specifically, changes in norepinephrine, dopamine, serotonin, and NPY have been identified as characterizing resilience (Krystal & Neumeister, 2009). Stressful events can cause a significant increase in levels of excitatory neurotransmitters such as norepinephrine and dopamine, can disrupt serotonin homeostasis, and can diminish brain levels of inhibitory neurotransmitters such as GABA, consequently influencing the function of specific brain regions and associated behavioral outcomes. Resilient individuals are identified as maintaining a more balanced state of these neurotransmitters in the face of stress or traumatic events and as returning to a balanced state when disruption of these biochemicals does occur (Bowirrat et al., 2010).
The greatest concentration of norepinephrine in the brain is in the region of the locus coeruleus in the brain stem. When activated by stress, the locus coeruleus releases norepinephrine into the brain, activating the HPA axis and influencing the balance of stress-related hormones. Elevated levels of the catecholamine norepinephrine are identified in individuals who suffer from anxiety. Animals who were treated in such a way as to block norepinephrine release were not able to respond in an anxious way to a fear-inducing stimulus, supporting the role of norepinephrine in anxious behavior (Peng et al., 2016). Several studies have found that individuals who practice meditation are able to maintain significantly lower levels of norepinephrine compared to control subjects who do not meditate. Change in the stability of norepinephrine levels has been found to correlate with improved quality of life and other indices of health (Curiati et al., 2005). Those who practiced meditation had lower levels of norepinephrine, higher scores on quality of life, and lower levels of concern for heart disease. These findings suggest that mindfulness practices may help to mediate resiliency through a catecholaminergic mechanism involving norepinephrine.
Experiencing stressful events is also associated with elevated levels of dopamine in the brain. Dopamine, like norepinephrine, is a catecholamine neurotransmitter that initiates cortisol release through activation of the stress response. Activation of the stress response is an adaptive mechanism in response to an environmental situation that requires activation of the arousal system—basically physical exertion, such as competitive sports or fighting for your life. Elevated levels of dopamine may not only be appropriate but also actually adaptive in certain stressful situations. Dopamine is known to activate the nucleus accumbens, the reward center of the brain, and is associated with reward-motivated behaviors. For example, it is the activity of dopamine on the nucleus accumbens that prompts people to abuse cocaine. Cocaine stimulates dopamine receptors in the nucleus accumbens causing rewarding feelings of intense pleasure. Similarly, some stressful situations may be motivating (e.g., competitive sports) in that they stimulate dopamine release and activate the nucleus accumbens. There are emotional rewards for engaging in some types of competitively stressful situations and succeeding. Other situations, however, may be traumatizing—such as fighting for your life. In life-threatening instances, the initial stressor activates both the stress response (the HPA axis) and the nucleus accumbens, providing motivation for action. However, after the stressor is gone, the stress response (fear) persists, while dopamine activation subsides. Other brain mechanisms may regulate whether dopamine release and related heightened arousal are associated with negative or positive outcomes.
Understanding the dual effects of dopamine—both activating the arousal system and regulating feelings of motivation and reward—can help us understand the role of dopamine in resiliency. Returning to the definition of resilience, we are reminded that resilience involves experiencing a stressful event or opportunity, being disrupted by it, and then returning to homeostasis, becoming even stronger in the process. This effect can be compared to the consequences of weight-lifting exercises that work out the muscles. The muscles are stressed by the exercise of lifting weights, which is followed by a period of recovery. The result of this exercise is that one becomes physically stronger and better able to cope with muscle exertion in the future.
In the case of resiliency, individuals are working out their brains to become more resilient; stress followed by a period of introspection and recovery eventually yields greater mental strength/resilience. Evidence suggests that mindfulness meditation practices involving introspective awareness are the mental exercises that can enhance resiliency through an underlying mechanism involving dopamine and related catecholamine actions in the brain (Rees, 2011). Mindfulness meditation activates dopamine receptors in the nucleus accumbens, without activating the HPA axis, resulting in greater feelings of motivation, inspiration, and pleasure.
Studies of the neurobiology of resilience suggest that GABA also plays a role in the ability to bounce back from adversity and regain equilibrium. Numerous studies have shown that lower levels of GABA and fewer GABA receptors are associated with higher levels of anxiety (Krishnakumar, Hamblin, & Lakshmanan, 2015). GABA modulates cortical excitability and neural plasticity. Since GABA is an inhibitory neurotransmitter, decreasing excitation in the brain, higher levels of GABA are associated with calmness, serenity, and even sedation—hence, the use of GABAergic pharmacotherapies such as Valium (diazepam) as anxiolytics and sedatives. Restoring homeostatic levels of GABA in the brain is associated with a more stable emotional state and greater resilience. Meditation has been shown to increase GABA levels in the brain and consequently decrease hyperexcitability and excess brain activation. Recent reports provide evidence that the practice of meditation results in production of higher levels of GABA and thus may serve a role in more resilient adaptation to normal brain biochemistry following a stressful experience.
Neuropeptide Y (NPY) is abundant in the hypothalamus and other regions of the brain and plays a role in processing stress, anxiety, the perception of pain, blood pressure, food intake, and energy homeostasis. Researchers evaluated the effects of mindfulness-based mind fitness training (MMFT) on NPY levels of Marines preparing for deployment and being put through a series of stressful training operations. Blood levels of NPY at the beginning of the study did not differ in Marines who received eight weeks of MMFT and those who only received training as usual. Nor was there a difference in NPY levels after eight weeks of training. However, following the stressful operations, Marines who had undergone mindfulness training had significantly lower levels of NPY than Marines who had only standard training. These differences in NPY levels correlated with faster heart rate recovery and faster rates of recovery from brain activation in the insula associated with greater emotion regulation.The authors in this study conclude that mindfulness training facilitates resiliency as measured by a quicker recovery and more adaptive response to NPY levels following stress. Specifically, MMFT was found to modulate NPY mechanisms underlying recovery from stress in active-duty military personnel when taught along with standard training for deployment (Johnson et al., 2014).
Galanin is a neuropeptide that plays a role in both the central nervous system (CNS) and gastrointestinal tract. Galanin regulates neural activity in the hypothalamus, locus coeruleus, cortex, and brain stem and alters the plasticity of neurons, including promoting neurogenesis in these regions of the brain that mediate resilience. Galanin is found to modulate the monoamines of serotonin, dopamine, and norepinephrine as well as NPY in these stress-responsive areas of the brain. Although research is yet to evaluate the effects of meditation on galanin activity, several studies have found that exercise activates gene expression of galanin, thus preventing activation of neural stress pathways. Similarly, it would be worth evaluating the role of meditation in releasing galanin’s neuromodulatory mechanisms to relieve stress and enhance resiliency.
Allostasis and homeostasis appear to be physiological mechanisms that can be enhanced through behavioral strategies involving mindfulness practices (Alim et al., 2012; Bowirrat et al., 2010; Goodyer, 2006; Sinha et al., 2016). Given that mindfulness exercises are proving to be a behavioral intervention that can be used to modulate cortisol, DHEA, and CRH levels, enhance allostasis, and restore homeostasis (Bränström, Kvillemo, & Åkerstedt, 2013), meditation may rebalance essential biochemicals to include those associated with the stress response, PTSD, and other mental health indices. The more practice one has in mindfulness meditation, the higher the measures of mindfulness, and the lower the increase in cortisol, DHEA, and CRH in response to stressful events. To that end, mindfulness decreases the allostatic load.
By definition, the psychological profile of the nonresilient individual is one who is easily affected by stress and is slow to return to a normal or functional state following a stressor (e.g., remains traumatized). Alternatively, the resilient individual is both able to maintain homeostasis during a stressful experience and is able to regain homeostasis when he or she is disrupted by the challenge of a stressful experience. These psychological traits have a physiological basis reflected in the biochemical mechanisms that have been described. Meditation is the practice that impacts the neurobehavioral mechanisms that are the foundation of resilience (Wang, Xu, & Luo, 2016).
Taken together, the results of numerous studies suggest that a certain biochemically balanced state may characterize resilient individuals and that these physiological mechanisms for establishing and maintaining biochemical balance may be the foundation of the psychological traits of resiliency. Furthermore, these physiological mechanisms for rebalancing can be activated through behavioral strategies. Research suggests that these behavioral strategies are the active ingredients of the practice of mindfulness meditation.
There are many forms of meditation; the difference in the various practices is the element of the focus. Mindfulness practices are defined by a focus on interoceptive experiences. Also referred to as somatic sensing or body scanning, interoceptive awareness is the practice of attending to all forms of sensory experience as they arise. For example, in a body scan, one may begin with a focus on the toes (or the head) and gradually move through the body, exploring the sensations arising in an ascending (or descending) order. Somatic sensing refers to any sensations arising from the body. In mindfulness meditation, one explores the sensations that arise within the body. In addition to the body scan, the movement of the breath is a common point of focus as an interoceptive experience, though there are many others. The breath is a useful point of focus, in that the exhale of the breath naturally activates the parasympathetic relaxation response and can contribute to allostasis and homeostasis in the presence of a perceived potential threat. The use of the breath as a point of focus is characteristic of many mindfulness practices, including seated meditation as well as yoga, tai chi, and qigong.
When one directs his or her point of focus toward sensations arising from the body, afferent nerve pathways are activated to send information through the vagus nerve into the brain stem. It is here in the brain stem that the norepinephrine pathway arising in the nucleus called the locus coeruleus relays information to the thalamus for processing (Aston-Jones, Shipley, & Grzanna, 1995; Berridge & Waterhouse, 2003; Hurley, Devilbiss, & Waterhouse, 2004). The thalamus serves to modulate, amplify, or inhibit sensory information transmission to the cerebral cortex where it is processed as part of the consciousness. Sensory information including seeing, hearing, tasting, touch, and somatic sensations arising from the viscera, the heart, and elsewhere are gated through the brain region of the thalamus. Only olfactory information coming through the nasal epithelium is able to bypass the thalamic gates and goes directly into the sensory cortex. Sensations of pain (nociception) are also transmitted via the vagus nerve and gated by the thalamus. This thalamic gating mechanism (Norris, 2016) is dependent upon the state of arousal and attention of the organism (Price, 1995; Simpson et al., 1997; Simpson, Waterhouse, & Lin, 1999). In addition to afferent input from the sensory receptors, other input to the thalamus is received from the hypothalamus. Hypothalamic activation of the thalamus is associated with selective closing of thalamic gates, particularly those providing somatosensory information from the periphery of the body. Selective thalamic gating translates into enhanced ability to focus on visual or auditory information and suppressed awareness of bodily sensations.
Ignoring somatosensory input during traumatic stressful situations may be adaptive in that somatosensory pain is often associated with these situations. In a fight-or-flight situation, attending to pain could be distracting from attending to other more relevant stimuli that could be critical for survival. For example, during stress or trauma, people often do not notice a wound or an injury. The focus remains on the battle at hand. It is not until later, once the battle is over, that one may notice an injury and the pain associated with it. Stress activation of the hypothalamus, in addition to activating the pituitary and adrenal cascade, simultaneously activates the gating mechanisms of the thalamus, blocking somatosensory input to the sensory cortex, and enabling the critical decision-making cortical region of the brain to remain focused on the external environment. Breath-holding facilitates sympathetic activation of the hypothalamus and is something that most individuals do when they are startled, afraid, tense, or dealing with a traumatic fight-or-flight situation. Dealing with stress or trauma activates the HPA axis, closes the thalamic gates to somatosensory processing, and heightens focus on selective external stimuli. The thalamic gating of somatosensory information allows the cortical regions of the brain to hyperfocus on processing only sensory information critical for survival.
The first key to reopening the thalamic gates is deactivation of the stress response. Once the HPA axis is deactivated, the thalamic gates are free to reopen. Mindfulness practices that focus on somatic sensing can hasten restoration of flow of sensory messages from the body. By intentionally directing the focus of awareness on the body, the thalamic gates are invited to reopen to receive somatosensory input. By intentionally focusing on the breath, breathing patterns may become normalized, and parasympathetic activity may facilitate thalamic opening. Here is where experienced practitioners issue warnings to proceed with caution. When these gates open, a flood of suppressed experience is invited into the consciousness and can overwhelm the inexperienced practitioner. For an inexperienced mindfulness practitioner who suffers visceral or other pain or trauma to the body, the rehearsed reaction to this experience has been to divert the awareness elsewhere, close the thalamic gates, and suppress any pain that may have started to arise—what psychologists refer to as denial or repression. Ignoring the pain, or repressing it, has become a conditioned coping strategy. Mindfulness is not a coping strategy—it is a healing strategy. In a safe environment, perhaps with support, mindfulness practices can gradually train the practitioner to open to somatic experiences, reopen the thalamic gates, release stored trauma, and gradually release and recover from a state of blocked feelings and emotional numbness. Continuing to focus on respiratory processing will continue to normalize breathing patterns and facilitate the release of suppressed experiences coincident with parasympathetic activity as opposed to stress.
In this author’s research with veterans who suffer from chronic pain, as they begin a mindfulness practice, the first thing that they note is that they become more aware of the pain (Nassif et al., 2015). They might report that they feel the pain more, but their explanations reveal that they are simply more conscious of the pain; that is, it has always been present, but that they had been ignoring it, resisting letting their awareness notice the pain. As a result, in their mindfulness practice, when they pay attention to pain, it seems more present. This mindfulness practice of interoceptive awareness is the active process of opening the thalamic gates to allow the nociceptive experience to flow from vagal afferents through the brain stem nucleus of the locus coeruleus and then through the thalamus into the insular and sensory cortices where awareness is perceived. In the relaxed state, with the thalamic gates open, bodily states associated with feelings are transmitted to the insular cortex and give rise to consciousness of emotional experiences. Releasing resistance by opening the thalamic gates allows the flow of information into the brain and restores the flow of neural processing involving multiple transmitter systems and related biochemicals. Homeostatic states can again be achieved.
Hölzel et al. (2011) identify several behavioral activities associated with mindfulness practices: (1) attention regulation; (2) body awareness; (3a) emotion regulation and reappraisal; (3b) emotion regulation: exposure, extinction, and reconsolidation; and (4) change in perspective on self. Correlated with these behavioral activities are changes in the underlying neural substrates of the behavior.
As mentioned previously, nociceptive experience is received from vagal afferents through the thalamus. These bodily sensations are then processed in the insula, which is located deep within the cerebral cortex of the brain. Several studies have demonstrated that the insula regulates interoceptive awareness (Craig, 2003, 2009; Critchley et al., 2004; Hölzel et al., 2011) and processing of social-emotional behaviors as well as pain and other sensorimotor experiences (Chang, Yarkoni, Khaw, & Sanfey, 2013). Specifically, the anterior insula is associated with awareness of the visceral states associated with emotions (Craig, 2003.)
Information from the insula is further processed in the anterior cingulate cortex (ACC), which is the area of the brain associated with attention regulation and emotional processing and is known to be the locus of self-regulatory behavior (Etkin, Egner, & Kalisch, 2011). The cingulate cortex is situated above and adjacent to the corpus callosum, in the medial wall of each cerebral hemisphere. It is unique in that it has connections to both the limbic system and the prefrontal cortex, connecting emotional processing with cognitive processing. Studies using functional neuroimaging have shown that PTSD is associated with reduced activation of the cingulate cortex. Similarly, depression and related forms of emotional suppression and emotional numbing such as substance abuse and suicidal ideation are also associated with decreased response in the cingulate cortex following an emotional experience (Stevens, Hurley, & Taber, 2011).
Physical or emotional trauma, which may lead to depression or numbness, blocks somatic sensation by closing thalamic gating mechanisms. Conditioning causes them to remain closed, and continual activation of the HPA axis becomes a habit. Resilient individuals, however, have learned to reopen these subcortical gating mechanisms following a stress or trauma, thus allowing information about the somatic state to enter the ACC. Studies of resiliency show that resilient individuals have larger volumes and greater gray matter density of the ACC (Kasai et al., 2008; Rauch et al., 2003; Woodward et al., 2006). Using functional magnetic resonance imaging or functional MRI (fMRI), Hölzel et al. (2007) found that the practice of focused attention meditation leads to greater activation of the ACC.
Meditation instructions to maintain focus on interoceptive processing can improve ACC function. Meditators’ self-reports indicate that with practice, it becomes easier to maintain focus on a single interoceptive sensation. Meditation practice also correlates with growth in the ACC region of the brain (Hölzel et al., 2007). The meditative practice of directing, and redirecting if necessary, one’s focus to his or her somatosensory experience may serve to enhance the capacity for emotional regulation and self-control through neuroplastic developments of the ACC, leading to greater levels of resiliency (Thomas & Plummer Taylor, 2015). Taken together, these data suggest common neural substrates and circuitry underlying resilience and meditation. Given this common physiological substrate, meditation practice may provide a behavioral mechanism for increasing resilience.
As mentioned earlier, the ACC is connected to both the limbic system and the prefrontal cortex. This connection is part of a network of brain areas that are implicated in self-referential processes. Known as the default mode network (DMN), these cortical and subcortical areas are active when the brain is at rest (Greicius, Krasnow, Reiss, & Menon, 2003; Mason et al., 2007; Raichle et al., 2001). When disengaged from attentional control or specific goal-directed behavior, neuroimaging studies of the brain’s resting state have shown activity in the medial prefrontal cortex (mPFC), posterior cingulate cortex (PCC), the ventral anterior cingulate cortex (a subregion of the ACC), hippocampus, and amygdala, which are areas associated with self-perception, emotion, memory processing and integration, and planning. Thus, activity in the DMN may serve as a baseline of cognitive activity that is self-referential, providing a narrative for a self across time that assesses the salience of internal and external information and attributing meaning and context among disparate, subjective experiences (Farb et al., 2007; Mason et al., 2007). While DMN activity may be adaptive in underlying the establishment of a narrative, consistent sense of self that can plan future activity, engage in introspection, recall important details, and attend to multiple, concurrent tasks, this default mode is also characterized by stimulus-independent thought, or mind-wandering, and may also subserve automatic and ruminative thought processes. For example, increased DMN connectivity, particularly in the mPFC and ACC, which are brain areas implicated in self-referential and emotional processes, is correlated with major depression, excessive rumination, and anxiety (Coutinho et al., 2016; Sheline et al., 2009).
In contrast, goal-directed tasks or shifts in attentional control appear to dampen or inhibit DMN activity. For example, mindfulness meditation shifts attention away from a narrative, self-referential focus to present-moment awareness. Neuroimaging studies have shown that this attentional shift activates corresponding brain structures that are involved in attention, interoception, and sensory processing (Farb et al., 2007; Hölzel et al., 2011; Lazar et al., 2005), areas of the brain that are distinct from the DMN and when activated serve to attenuate or disengage DMN associated activity. Meditation can attenuate activation of the DMN, particularly in the mPFC and PCC, while facilitating a stronger connection between the PCC, dorsal ACC, and dorsolateral prefrontal cortices. This may indicate greater cognitive control and self-monitoring as well as greater attentional focus (i.e., decreased mind-wandering; Brewer et al., 2011). In addition, these areas of the cingulate cortex (i.e., PCC and ACC) are connected to the nucleus accumbens and hypothalamus, which may provide an important link between higher cognitive control processes and more basic, emotional processes perhaps by modulating affective and autonomic states (Greicius et al., 2007). This connection and modulation among cognitive, sensory, and emotion cortices supported by meditation may allow for more adaptive, skillful responses to stressful or emotionally salient experiences, providing a neurobehavioral basis for the effectiveness of meditation in attenuating depression, anxiety, and stress, thus building resiliency.
Actively practicing body sensing/interoceptive awareness during the mindfulness exercise is a critical ingredient of the practice that enables recovery from pain. One of the key elements of interoceptive awareness is the sensation of the breath moving into, through, and out of the body. Since exhalation of the breath is associated with parasympathetic activation of the relaxation response, mindfulness practices that use the breath as an element of interoceptive focus may be particularly helpful in attenuating hypothalamic activity associated with hyperfocus, allowing the thalamic gates to reopen and reestablishing somatic processing all at once. To the practitioner, it intuitively makes sense that focusing on the breath enables coping and management of pain. It also allows the healing mechanisms of the brain to engage.
When we pause to consider pain from an evolutionary perspective, it makes sense that pain serves an adaptive function. When there is an injury to the body, the brain should become aware of the injury in order to move the body away from the source of the pain and to coordinate the healing response. By definition, what the brain perceives as an injury must be a “negative” experience, in this case what we refer to as pain. The sensation is intended to draw our awareness to the sensation. In this awareness, the CNS (brain) can coordinate the healing mechanisms needed to preserve, restore, and regenerate the injured body. With this neural integration of awareness of the entire physical being, the dynamic activity of healing can occur.
A later evolutionary mastery in the phylogenetic development of the nervous system is the ability to override awareness and ignore pain. This ability to suppress awareness may also have served an adaptive function. Indeed, this is an ability taught in military training and practice. The ability to close the thalamic gates and “good-soldier” through all forms of trauma is a recognized quality of the so-called good soldier. Abandoned in this closed condition, however, the brain’s ability to integrate with the periphery of the body and coordinate internal healing mechanisms is blocked. The soldier remains in a hyperfocused state, attending primarily to visual and auditory stimuli and suffering from chronic activation of the HPA axis. The experience is described as one of feeling hypersensitive to sounds and sights and constant or chronic experience of stress and anxiousness. It is also described as a sense of emptiness or numbness of the body (including the heart) and a lack of sensate awareness of the body—an inability to feel, literally. In this state, serious physical and emotional conditions can begin to develop and are left unattended by the brain and related CNS coordination.
Mindfulness is the antidote to this training and can allow the soldier to heal. Moreover, it is a tool that can be used in advance of exposure to trauma to build resilience by training the soldier to stay present to a broader range of sensorial experience. Just as we train soldiers to build muscular strength and capacity, we can use mindfulness exercises to train our soldiers to build mental strength and capacity, reflected in neuroplastic growth in the brain. The field of mindfulness would suggest that the soldier can be trained to stay present to a fuller degree of conscious awareness and, when stressful or traumatic distractions are encountered, to use mindfulness strategies to return to homeostasis and present-moment awareness, thus enhancing resilience and preventing and treating mental health problems in the military.
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