Abstract

Introduction

Meditation practices that are derived from Buddhist traditions have been gradually adopted in the West and have become a topic of widespread interest in both science and medicine. In order to fit with modern Western values and worldviews, the practices have been largely decontextualized from their original Buddhist goal of awakening and recontextualized as clinical interventions or forms of psychological and physiological self-maintenance.¹ This recontextualization has resulted in a modification of the traditional goals of practice and also in the way scientific studies report on the effects of meditation, which may emphasize or de-emphasize certain aspects of Buddhist formulations to serve modern needs and values.^2,3

For example, Buddhist texts describe meditation practice as aiming to cultivate a state of relaxed alertness, and therefore must continually balance between the extremes of hyperarousal, agitation, and restlessness on the one hand, and hypoarousal, excessive relaxation, mental dullness, and sleep on the other (Fig. 1).^4–6 Within the modern context, however, much more emphasis has been placed on the relaxing effects of meditation without as much attention to the arousing or wake-promoting effects. In some modern formulations, the goal of meditation has expanded beyond relaxation and decreased arousal^7–10 to include a state of consciousness that is deliberately half-asleep, a “physiological twilight condition between waking and sleep,”^11–13 equivalent to sleep,^{14, 15} or a form of sleep-like hibernation, a “shallow torpor”¹⁶ that is reversed by (i.e., the opposite of) wakefulness.¹⁷ As a result, meditation practices are often equated with non-specific relaxation techniques⁷ where hypoarousal and sleep are seen as desirable rather than obstacles to concentration (samâdhi).¹⁸

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Figure 1

Meditation maintains a state of relaxed alertness by guarding against the extremes of hyperarousal (excitation, restlessness, anxiety) and hypoarousal (laxity, drowsiness, sleep).

In contrast to modern formulations that emphasize the hypoarousal end of the spectrum, traditional Buddhist texts tend to emphasize vigilant wakefulness as a means to a profound shift in perception called awakening (bodhi). Because meditation must balance mental laxity and agitation, relaxation is infused with courageous energy (viriyâ), zeal (atapi), and an alert vigilant awareness such that a practitioner is devoted to wakefulness (jâgariya), and guarded against the hindrances of drowsiness and sleep.^19,20 Scholars familiar with the traditional Buddhist goals of meditation have criticized Western scientists for their overemphasis on relaxation.^1,21 In his Science and Buddhism: A Guide for the Perplexed, Buddhist studies scholar Donald Lopez laments “Where is the insistence that meditation is not intended to induce relaxation but rather a vital transformation of one’s vision of reality?”²² Others warn how “a practice that only relaxes the mind might eventually prove harmful.”²³

As an attempt to promote a more balanced view of the goal of mindfulness meditation, Jon Kabat-Zinn changed the name of his program from Stress Reduction and Relaxation Program²⁴ to Mindfulness-Based Stress Reduction (MBSR), characterized the term mindfulness as being awake,²⁴ and removed the word relaxation from audiotapes and handouts. Similar attempts to point out the arousing effects of meditation have been widespread^11,16,23 but also lost in the well-established enthusiasm around relaxation and its closely-related cousin, sleep.

In an attempt to counterbalance the plethora of data demonstrating the relaxing and hypoarousing effects of Buddhist meditation, this interdisciplinary review aims to provide evidence of meditation’s arousing or wake-promoting effects by drawing from both scientific studies and Buddhist textual sources. The construct of arousal is complex and multidimensional, with multiple distinct but overlapping inputs, including from cortical, autonomic, endocrine, cognitive, and affective systems.²⁵ While other reviews have focused more on somatic forms of arousal,²⁶ this review will focus on the cognitive dimensions of arousal that pertain to wakefulness and alertness.

The link between attention and wakefulness

While there are many different forms of meditation, most agree that the deliberate training of attention, either in a focused and directed or open and receptive way, is a foundational part of any meditation. This review emphasizes two common forms of attention training, focused attention (FA) and open monitoring (OM), which are foundational in Buddhist and many non-Buddhist meditation practices.²⁷

Attention has been typically divided into three basic functionally and anatomically distinct types: orienting, executive attention, and alerting.^28,29 Orienting directs and limits attention to a selected stimulus. Executive attention, also called conflict monitoring or selective or focused attention, involves prioritizing among competing tasks or responses. Alerting consists of achieving and maintaining a state of mental preparedness and a high sensitivity to incoming stimuli, and is subdivided into phasic alertness and tonic alertness. Phasic alertness refers to the ability to increase response readiness briefly following a cue or warning signal. Tonic alertness, also called intrinsic alertness or vigilant attention,³⁰ is a general level of arousal, alertness, vigilance, wakefulness, or state of mental preparedness to detect or respond to infrequent or unexpected stimuli. Tonic alertness can also be measured by its deficit: a general level of sleepiness, fatigue, or lack of sustained attention characterized by an attentional lapse or mind wandering.³¹ Because tonic alertness provides the cognitive tone for performing more complicated functions, such as working memory and executive control,^32,33 it is thought that all other forms of attention are dependent on tonic alertness.³⁴ Studies of alertness training^35–38 or pharmacological enhancement of alertness³⁹ leading to improvements on a broad range of attentional tasks also support the idea that tonic alertness is a foundational prerequisite for other forms of attention. While all three types of attention have been researched in meditation studies,^40–53 less emphasis has been placed on tonic alertness. Furthermore, tonic alertness has been described in terms of increased sustained attention or vigilance^40,49,54,55 but not in terms of increased wakefulness or arousal, an approach influenced by the modern Western view that meditation promotes relaxation and sleep rather than wakefulness.

The positive relationship between attention and arousal or wakefulness is evident in common everyday experiences. We have all noticed, for example that paying attention, as well as learning, remembering, and regulating emotion, are more difficult when we are tired, or that intensely engaging attention before bed can inhibit sleep. The idea that attention is positively correlated with greater arousal and wakefulness is well-established within the fields of sleep and chronobiology,⁵⁶ but this correlation has been relatively unexplored within the field of meditation research. Thus, this review will adopt a sleep researcher’s approach in order to examine the effects of contemplative practices on tonic alertness as defined by the complementary domains of sleep propensity and wakefulness. Specifically, this review will investigate the effects of Buddhist meditation on the following indices of sleep propensity/wakefulness: (1) the activation of sleep/wake–related brain areas, (2) subjective reports of sleepiness/fatigue, (3) electroencephalogram (EEG) activity during wakefulness, (4) behavioral measures of vigilance/sustained attention, (5) EEG during sleep, and 6) sleep duration.

Meditation effects on tonic alertness

Functional connectivity

In addition to activation of alertness-related areas and deactivation sleep-related areas, functional connectivity (FC) or correlated activity between brain areas can also serve as an index of sleepiness or wakefulness. The fading of consciousness during non-rapid eye movement (NREM) sleep is thought to be associated with the breakdown of effective connectivity between multiple cortical areas,¹¹⁹ specifically within nodes of the DMN, and between the DMN and attention network.

Less sleepy during wake

More awake during sleep

In many Tibetan Buddhist¹⁶¹ and also non-Buddhist traditions,¹⁶² the goal of cultivating of vigilant awareness in every waking moment is extended beyond the waking state to sleep states as well. One teacher instructs “When you fall asleep, you are asleep with virtually full awareness.”¹⁶¹ Several studies have described meditators’ self-reports of ongoing conscious awareness during sleep.^162,163 In support of such increased wakefulness during sleep, several polysomnographic sleep studies have found greater cortical arousal during sleep in meditators, including increased stage-1 sleep, alpha-theta (wake-like) EEG, arousals, reduced slow-wave sleep,^{144, 162,164} and increased gamma.¹⁶⁵

Ferrarelli et al.¹⁶⁵ found that long-term meditators had increased parietal-occipital EEG gamma power (25–40 Hz) during whole-night non-rapid eye movement (NREM) sleep compared to non-meditating controls. Increased gamma was positively correlated with the length of lifetime daily meditation practice (Spearman’s rho= 0.475, P< 0.02). In an EEG-based longitudinal randomized controlled trial (RCT), Britton et al.¹⁶⁴ found increased wakefulness and decreased sleep propensity following Mindfulness-Based Cognitive Therapy (MBCT) that was correlated with improved mood and meditation practice amount. Over the course of the trial, the MBCT group increased in stage-1 minutes, awakenings, and arousals, and decreased in percent of slow-wave (stage 3 and 4) sleep compared to waitlist controls. Each of these objective indices of increased cortical arousal was correlated with amount of home meditation practice in a linear dose-dependent fashion, which further supports that the increased arousal was due to meditation. Although there was no overall treatment effect on sleep duration, average (diary) total sleep at post-treatment was negatively correlated with minutes of daily practice, so that more meditation was associated with less sleep (Fig. 2A–D).

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Figure 2

Correlation between meditation practice and changes in sleep or arousal variables following MBCT, including (A) stage-1 minutes, (B) arousal and awakenings, (C) slow-wave sleep (SWS) percent, and (D) total (diary) sleep time. Figures A–C reprinted, with permission, from Britton et al.¹⁶⁴

There are several lines of evidence to suggest that these increases in cortical arousal are beneficial and desirable, rather than indicators of poor sleep or insomnia. First, these indices of increases in cortical arousal were also associated with an improvement in depression (Beck depression inventory (BDI) scores)), including increased awakenings, arousals, stage-1 minutes, as well as reduced overall sleep time (r= –0.60), so that the larger increase in cortical arousal, the larger the decrease in depression scores.

Meditation and sleep amount

Decreased sleep duration in meditators during periods of intensive practice, such as multiday silent retreats is a well-known phenomenon²⁷ and is considered a sign of meditative proficiency and progress.¹⁹ Kornfield¹⁶³ documented decreased sleep duration in Theravada Vipassana meditators on 3-month retreats (12–15 h of meditation/day) compared to a control group who meditated 1–2 h/day. Seventy percent of the retreat participants reported an average 2 h decrease in sleep duration in comparison to 10% of controls, who also reported increases in sleep duration (10%). The periods of sleep decrease were associated with periods of greatest self-reported and teacher-observed mindfulness.

In a qualitative study in our laboratory, a meditator who had completed a 3-month Tibetan-style shamatha retreat (12–15 h/day), reported that for the first 2 weeks of the retreat, her sleep duration initially increased to 8 h/night before gradually diminishing to 1.5–3 h/night by the eighth week. Buddhist texts suggest a nocturnal sleep time among proficient meditators of approximately 4 hours.¹⁹

Other studies have begun to assess the effects of daily meditation practice on sleep duration outside of a retreat context. Kaul et al.,⁵⁵ measured 15 days of diary-reported sleep in a small sample of experienced Indian meditators (n=7) who practice focused (breath) awareness techniques 1.5–3.5 h/day (for at least 3 years) compared to matched non-meditating controls (n=23). Sleep diaries indicated a significantly shorter average nocturnal sleep duration in meditators than controls (5.2 h vs. 7.8 h, P< 0.00001).

A recent study examined sleep duration of meditators in daily life, using objective, EEG-based measures of sleep in a much larger sample. This cross-sectional study¹⁶⁵ recorded single-night polysomnographic sleep studies (high-density EEG) in long-term (8700 average lifetime meditation hours) Tibetan and Theravada Buddhist meditators and age- and gender-matched non-meditating controls. The meditators had a significantly reduced total sleep time (6.2 vs. 6.7 h, P= 0.001) as well as increased minutes of wake after sleep onset (74 vs. 44 min, P =0.003) compared to controls.

In contrast to advanced Buddhist mediators who view decreased sleep as a sign of progress, modern clinical applications seek to increase sleep duration and depth with meditation practice. High-quality empirical support for clinically-oriented meditation programs, such as MBSR, promoting sleep have not been particularly strong (see Ref. 166 for a review) and often lack objective measures of sleep, particularly EEG. While some RCTs have found positive effects of meditation training on self-reported sleep quality^167–169 other RCTs have found no difference from controls.^170–172 Subjective ratings of sleep quality appear to be more affected by meditation than specific sleep parameters (such as sleep duration)^173,174 with both positive and negative changes in arousal when measured by objective measures of quality.^167–169 After many mixed or equivocal studies of MBSR, some sleep researchers have suggested that “mindfulness meditation as a single intervention might not yield strong effects on sleep”¹³² and instead created programs that include mindfulness as part of a multicomponent cognitive-behavioral sleep treatment.^132,175 As an indication of the current state of the research, the most recent (2012) U.S. Government Report judged the level of evidence of clinically-oriented meditation programs for improving sleep to be insufficient.¹⁷⁶

What factors determine whether meditation training will increase or decrease arousal, and promote wakefulness or sleep? This is an important research question that is largely unknown, but probably encompasses a number of factors, including dose and type of practice, sample characteristics (condition/disorder), degree/type of sleep disturbance, comparison group, concurrent medication,¹⁶⁷ and age and method of measuring sleep or wakefulness (subjective/objective).

Non-linear progress

In order to make sense of the mixed and contradictory findings, it may help to approach the trajectory of meditative expertise as non-linear in regard to arousal and tonic alertness.¹⁷⁷ Specifically, relaxing and sleep-promoting effects might be expected at low doses or early stages of practice (such as an introductory 8-week program), but more alertness, wakefulness, and less sleep as dose or practice progresses. Britton et al.¹⁷⁵ found that as little as 5–10 min/day for 2–3 days/week (<1 h/week) increased self-reported sleep duration by more than an hour, but that as practice times approached 30 min/day (>3 h/week), then sleep duration began to decrease (Fig. 2D) and cortical arousal began to increase (Fig. 2A–C).¹⁶⁴ Similarly, our 3-month retreat participants slept more during the first 2 weeks, then progressively less, in line with findings of decreased sleep following intensive¹⁶³ or long-term daily practice.^55,165

Both Buddhist sources and recent research support the idea that early stages of practice require more effort and produce more fatigue than later stages of practice.^27,178,179 Most beginning meditators start with a form of focused attention training, which relies on orienting, executive, and phasic alerting forms of attention. Like training a muscle, attention is redirected from self-referential thought back to the meditative object, over and over until attentional stability can be established. Proficient meditators can disengage faster and more easily from self-referential thought (DMN activity).⁶⁵ Attention enhances efficiency of sensory information processing and enhances sensory acuity by increasing the ratio of signal to noise in neural communications.¹⁸⁰ Meditation-related increases in perceptual sensitivity and sensory acuity^{43, 181–183} require less cognitive resources and effort for stimulus detection and therefore free up resources to be available for other functions.^43,54 Like having stronger muscles, more efficient processing is less taxing or fatiguing and supports more enduring alertness. Reports that increases in directed attention/phasic alerting leads to improved tonic alertness^49,184 support Kabat-Zinn’s statement that “By paying attention you literally become more awake.”¹⁸⁵ Indeed, many studies have found positive correlations between meditative expertise (practice amount) and subjective, neurological, and behavioral measures of wakefulness (see Table 2).

However, the relationship between phasic and tonic alertness is more likely bi-directional and mutually reinforcing,^35–38 as the resources that are freed up by more efficient processing (sensory acuity) can promote a form of tonic alertness that makes the meditator more aware of internal and external stimuli,^{43, 54, 186} thus leading to more efficient processing, until the system runs so effortlessly that it may require much less recovery time (i.e., sleep).

Neuroimaging studies are beginning to support a non-linear trajectory of meditative practice and proficiency. Brain areas underlying tonic alertness are activated in early stages of training, compared to non-meditators, but these areas begin to deactivate as meditative expertise becomes more proficient and effortless in later stages.^{45,86,178,187} This eventual effortlessness that accompanies increased efficiency in later stages is thought to arise from increased connectivity between brain areas that were previously not co-activated.^{99,125,178,188}

Thus, the point when meditation practice no longer produces drowsiness and sleep, but instead engenders increased and sustained wakefulness, may be an indicator of the neuroplastic changes that signify meditative proficiency. In this sense, “awakening” is not a metaphor, but rather an iterative process of neuroplastic modifications and increased efficiency that supports a new level of perceptual sensitivity and insight.

Conclusion

The purpose of this review was to provide evidence, by drawing from both scientific studies and Buddhist textual sources, of meditation’s arousing or wake-promoting effects in an attempt to counterbalance the common modern characterization of Buddhist meditation as a relaxation technique that promotes hypoarousal and sleep. Traditional Buddhist formulations and a host of recent subjective, behavioral, and neuroimaging studies of meditation suggest that Buddhist meditation practices may promote greater wakefulness and lower sleep propensity, especially as practice progresses. With a more interdisciplinary approach that includes traditional Buddhist formulations, the scientific study of meditation may gain a more comprehensive view of the full range of possible effects and applications of contemplative practices.

Acknowledgments

Footnotes

References