Neural Basis of Meditative Practices

Basics of Meditation

The most fundamental question in cognitive neuroscience is how the brain enables the mind's faculties, and as Francis Crick once quoted, "there is no scientific study more vital to man than the study of his own brain." Recent technological advancements in neuroimaging have allowed us to gain a deeper understanding of the structure and function of the brain. However, there is still a lengthy process involved in mapping out the exact networks associated with affective and cognitive attributes. While an MRI provides an objective report of neurobiological processes, meditation goes a step further by offering a subjective understanding of our internal states. One of the most powerful indices of cognitive functioning is the ability to bring the wandering mind back to the present and employ single-pointed attention. This ability is known as attentional control, where an individual volitionally chooses to pay attention to relevant and meaningful stimuli while inhibiting unnecessary information that may come from the outside (i.e., sensory modalities) or from the inside (i.e., cognitive processes). But why does this matter? Why should we strive to improve our attention in the first place?

Turns out, there is good evidence that suggests improving attention changes our neural networks in a way that improve emotion regulation [1, 2] and cognitive functioning [3]. These neural changes are highly valuable not only for remediating existing negative symptoms of affective disorders but also for enhancing positive traits that contribute to the preventative treatment of mental health conditions. Hence, the goal of this blog is to highlight current research on the neural basis of attentional control and then discuss various psychosocial benefits of mindfulness training for a wider audience. 

Altered Traits

One of the most famous compilations of scientific findings related to meditation practices comes from Richie Davidson's book, "Altered Traits." This blog aims to provide a brief summary of those findings while elucidating limitations in meditation research. In his book, Richie argues that meditation is one of the most powerful practices for developing a healthy mind, not only combating psychopathology but also changing fundamental aspects of our interbeing. According to Dr. Davidson and Dr. Goleman in "Altered Traits," there are four aspects of any contemplative practice that incorporates meditation: 1. Stress regulation, 2. Attentional control, 3. Compassion and Social Connection, and 4. Lightness of Ego/Selflessness. Each of these attributes can have a state or a trait associated with it. For instance, one can be in the state of regulating stress through deep breathing or one can possess the trait of always being tranquil. Similarly, one can be in the state of loving their partner or one can possess the trait of loving kindness towards everyone in the world. State-level effects of meditation are only temporary and limited compared to the long-lasting trait level benefits. Being in a state of mind provides contentment in that moment, however, as soon as the mindfulness training is halted, that contentment disappears. Trait level effects of meditation, on the other hand, withstand time, socioenvironmental and biological changes. As the authors of "Altered Traits" put it, "The after is the before for the next during." The after refers to mental changes that persist following meditation training, the before refers to mental changes prior to meditation, and the during refers to each consecutive session of mindfulness practice. In essence, the resting state of the brain is already at equilibrium that no change is seen before and after meditation. Such an effect is rare but possible through long term practice.

Ultimately, meditation practice leads to trait level changes that exist before, after, and during each meditation session. A healthy mind is one that can flexibly change its internal states while withstanding external changes, and the state-level benefits of meditation allow us to do so. However, an even healthier mind is one that is effortlessly stable and equanimous and any perturbations in biopsychosocial factors have little to no effects on the balance of mind. Richie's argument is that though short-term meditation practice can lead to state level changes, the potential effects of meditation are far more beneficial in the long term. The goal of meditation, thus, is to reach effortless tranquility and awareness that spreads boundlessly inside and outside the individual. These trait level effects manifest as changes in psychological well-being reported by subjective measures but are also observed through objective reports by neuroimaging and physiological data. Hence, the next section attempts to shed light on some of the neuroscience of attentional control and meditation practice.

Neuroscience of Attentional Control

One theory is that attentional control changes our prefrontal connectivity with limbic structures and promotes emotion regulation to reduce stress related symptoms [4, 5]. The salience network, known for its role in modulating attentional control, encompasses two pivotal executive regions: the dorsal anterior cingulate cortex (dACC) and the anterior insula. Both of these regions play a role in switching attention from internal to external flow of information and vice versa. The anterior insula plays a key role in reporting subjective states during attention and thereby sustaining awareness on relevant information. The dorsolateral prefrontal cortex (dlPFC) is in the central executive network and is involved in regulating autonomic arousal facilitated by amygdala. Thus dACC and anterior insula work together to enable the maintenance of attention, while the dlPFC inhibits amygdala activity, thereby reducing affective load and mitigating emotional distractions. [6]. The dlPFC also possesses inhibitory connections with the default mode network (DMN), responsible for self-referential thoughts and rumination on past events. The inhibition of the DMN during task-selective attention aligns with the Buddhist principle of non-self-meditation. In this meditation, practitioners are trained to observe the illusion of their self, scrutinize the stream of thoughts without positing an agent, and consequently cultivate a heightened single-pointed awareness of their breath. This practice, on the whole, involves the utilization of the salience network while inhibiting the DMN to optimize objective attention. [7]. A neutral object like our breath has no biological or psychological reward associated with it, so how the natural question is how do our brains learn to pay attention to something that doesn't give reward? Though awareness of the breath may not provide an external incentive, it may provide intrinsic satisfaction that reinforces the practice of meditation. It isn't easy, but like the old saying says, practice makes man perfect.

The neuroscientific explanation may also be elucidated by considering the insula's capacity to evaluate subjective experiences associated with relaxation and stress relief that result from single-pointed attention. Mindful breathing comprises two key components: relaxation and single-pointed attention. The meditator's attentive focus reinforces dorsolateral prefrontal cortex (dlPFC) inhibition over the amygdala, leading to a reduction in sympathetic arousal. Simultaneously, deep breathing activates the vagus nerve, enhancing parasympathetic tone and fostering positive subjective feelings [8]. Presumably, these positive feelings are appraised by the anterior insula and conveyed through neural connections to the dlPFC, which then further sustains attention and inhibits the DMN. In summary, meditation practice allows these brain structures to sustain attention even in absence of incentives and helps promote long term emotion regulation through the tonic control of amygdala and the default mode network.

The Buddha had taught that when the mind becomes content with even neutral, mundane, moment to moment activities such as breathing, it gives up craving for more things and starts to enjoy the little events in life. It is this persistent contentment and lack of dissatisfaction that alleviates most of the suffering and increases resilience despite negative events in our life. Perhaps, affective neuroscience is starting to catch to what the Buddha taught 2500 years ago.

Clinical application

Repeated transcranial magnetic stimulation (r-TMS), applied to the dlPFC, has received FDA approval as a safe and effective intervention for treatment-resistant depression. This approval is primarily based on evidence demonstrating improvements in emotion regulation in patients that do not respond to traditional therapies for depression [9]. The magnetic stimulation used to induce neuroplasticity in the dlPFC during r-TMS resembles meditation practices employed in metacognitive awareness, which involves the mind's ability to be conscious of its own internal landscape. Similar to TMS, meditation has exhibited the capacity to alter neural circuitry, leading to improvements in emotion regulation in clinical populations [10]. For instance, an 8-week mindfulness-based exposure therapy training in veterans with PTSD resulted in increased resting-state functional connectivity between the default mode network (DMN) and dlPFC, as well as DMN and dACC [11]. The interpretation of this may be that meditation is strengthening the ability of dlPFC and dACC to regulate activity in DMN to reduce mind wandering and rumination, but the exact mechanism is unclear. In addition to functional brain changes, long-term meditation has also been correlated with structural changes, such as increased prefrontal cortical thickness and increased hippocampal volumes[12, 13]. However, the connection between these structural changes due to meditation and alterations in clinical symptom presentation remains unknown, representing an avenue for future research.

Several randomized clinical trials have demonstrated improvements in worry and anxiety symptoms following mindfulness-based stress reduction (MBSR) training in experimental groups, compared to controls. [14, 15]. A study published in JAMA Psychiatry, a highly prestigious journal, found that when patients with generalized anxiety disorder (GAD) were randomly assigned either MBSR treatment or an antidepressant, both groups exhibited similar clinical outcomes post-treatment [16]. This may suggest that meditation training may be noninferior to psychopharmacological interventions. However, more longitudinal research is necessary to determine whether meditation can surpass first-line psychiatric interventions. Nevertheless, the extensive literature on the neuroscience of attentional control and findings from randomized clinical trials provide compelling evidence for the benefits of meditation in both clinical and non-clinical populations.

Limitations

Several neuroimaging studies in the literature only provide neural correlates of meditation practice and do not elucidate causal mechanisms. Furthermore, it remains unclear how mindfulness meditation differs from other lifestyle interventions, such as art therapy, relaxation techniques, and other cognitive-behavioral therapies. However, an increasing number of studies are conducting rigorous randomized control trials with active controls, offering a deeper understanding of the differential effects of meditation compared to other psychotherapies. Meditation is not a magic bullet for all conditions, and it certainly confers specific benefits relevant to particular clinical populations. For example, one study found that Mindfulness-Based Stress Reduction (MBSR) outperformed Cognitive Behavioral Therapy (CBT) in improving anxiety symptoms only in patients with moderate to severe depressive symptoms, whereas CBT outperformed MBSR in improving anxiety symptoms in those with highly anxious but mild depressive symptoms. [17]. Therefore, more studies are needed to investigate moderating factors of MBSR and other meditation treatments, ensuring their use in the most relevant scenarios. Potential moderators that could influence the efficacy of MBSR include personality, childhood trauma, sympathetic arousal, worry trait, and the severity of depressive symptoms. Research in meditation becomes even more complex considering the existence of different types of meditation, such as loving-kindness meditation and open awareness meditation. Thus, additional research is required to dissect the attributes of attention training observed in these contemplative practices and move beyond correlation to identify mean effect changes between meditation and other active control groups.

Lightness of Self

Clinical psychology aims to treat mental illness by altering cognitions, thoughts, and feelings, leading to changes in behavior. These behavioral changes ultimately contribute to a patient's development of a new sense of identity, fostering autonomy and volitional control over their life. The more these beneficial behaviors are activated, the better the patient feels, reducing the likelihood of relapse into clinical pathologies.

Similarly, existentialist philosophers contend that our profound mental distress often stems from an inability to find meaning in life, resulting from a lack of autonomy. We seek autonomy by attempting to alter the world around us to assert control. However, this pursuit often entangles us in an endless cycle of dissatisfaction with the current state of affairs. Buddhists recognized that the root of our suffering lies in the weight we carry regarding our sense of self—an illusion, in reality.

According to William James, the father of western psychology, the 'self' is an ever-flowing stream of conscious experiences, fluctuating based on biological and psychological states. Regardless of our efforts to satisfy the self, it is inherently predisposed to change and yearn for what it lacks. However, by releasing our grasp on the illusory self, we can gradually perform actions without becoming entangled in unending self-driven expectations. Instead, we can appreciate the world as it is, in its ever-changing form. This release of expectations and ego leads to lightness of self, which then manifests into a steady flow of nonjudgemental conscious experience. A flexible self lacks a fixed identity, adapting itself to the needs of the present moment. Each moment, then, feels like the most beautiful moment, lived without a yearning for more in the future or a desire for less in the present. As the old saying goes:

"Whatever comes, let it come, whatever stays, let is stay, and whatever goes, let it go." - HWL Poonja.

"Nature does not hurry, yet nothing is left undone."- Lao Tsu.

References

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2. Ma, S.T., et al., Neural circuitry of emotion regulation: Effects of appraisal, attention, and cortisol administration. Cognitive, Affective, & Behavioral Neuroscience, 2017. 17(2): p. 437-451.

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7. Garrison, K.A., et al., Meditation leads to reduced default mode network activity beyond an active task. Cogn Affect Behav Neurosci, 2015. 15(3): p. 712-20.

8. Ganguly, A., et al., Effect of meditation on autonomic function in healthy individuals: A longitudinal study. J Family Med Prim Care, 2020. 9(8): p. 3944-3948.

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11. King, A.P., et al., ALTERED DEFAULT MODE NETWORK (DMN) RESTING STATE FUNCTIONAL CONNECTIVITY FOLLOWING A MINDFULNESS-BASED EXPOSURE THERAPY FOR POSTTRAUMATIC STRESS DISORDER (PTSD) IN COMBAT VETERANS OF AFGHANISTAN AND IRAQ. Depression and Anxiety, 2016. 33(4): p. 289-299.

12. Luders, E., et al., The underlying anatomical correlates of long-term meditation: Larger hippocampal and frontal volumes of gray matter. NeuroImage, 2009. 45(3): p. 672-678.

13. Luders, E., et al., Global and regional alterations of hippocampal anatomy in long-term meditation practitioners. Human Brain Mapping, 2013. 34(12): p. 3369-3375.

14. Biegel, G.M., et al., Mindfulness-based stress reduction for the treatment of adolescent psychiatric outpatients: A randomized clinical trial. Journal of Consulting and Clinical Psychology, 2009. 77(5): p. 855-866.

15. Verweij, H., et al., Mindfulness-Based Stress Reduction for Residents: A Randomized Controlled Trial. Journal of General Internal Medicine, 2018. 33(4): p. 429-436.

16. Hoge, E.A., et al., Mindfulness-Based Stress Reduction vs Escitalopram for the Treatment of Adults With Anxiety Disorders: A Randomized Clinical Trial. JAMA Psychiatry, 2023. 80(1): p. 13-21.

17. Arch, J.J. and C.R. Ayers, Which treatment worked better for whom? Moderators of group cognitive behavioral therapy versus adapted mindfulness based stress reduction for anxiety disorders. Behaviour Research and Therapy, 2013. 51(8): p. 434-442.