Hatha Yoga and Executive Function: a Systematic Review
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THE JOURNAL OF ALTERNATIVE AND COMPLEMENTARY MEDICINE Volume 22, Number 2, 2016, pp. 125–133 ª Mary Ann Liebert, Inc. DOI: 10.1089/acm.2014.0091 Hatha Yoga and Executive Function: A Systematic Review Kimberley Luu, BSc,1 and Peter A. Hall, PhD, CPsych1,2 Abstract Introduction: Recent reviews have documented the beneficial effects of seated meditation on executive function (EF). However, there has yet to be a comprehensive review on the effects of Hatha yoga, a moving meditation, on EF. Objective: To examine the empirical literature on the effects of Hatha yoga on EF. Methods: MEDLINE, Scopus, and PsycINFO databases were searched for experimental studies (between- or within-subject designs) testing the effects of Hatha yoga (acute bouts, short-term interventions, longer-term interventions) on EF. Results: A total of 11 published studies met eligibility criteria: Three studies involved healthy adults, 2 studies involved healthy older adults (n = 2), 1 study involved children and adolescents, and 5 studies involved medical (n = 4) or forensic (n = 1) populations. In healthy adults, 2 of 3 studies suggested that acute bouts of Hatha yoga improved EF; however, 1 study using a short-term intervention found no improvements in EF. Among healthy older adults, 1 study provided evidence that Hatha yoga improves EF. In child/adolescent samples, 1 study supported the contention that Hatha yoga improves EF after short-term interventions. Among medical populations, EF improved in patients with type 2 diabetes mellitus and in 1 of 3 studies involving patients with multiple sclerosis. The sole study involving impulsive prisoners showed positive effects on EF with a short-term intervention. Conclusion: Hatha yoga shows promise of benefit for EF in healthy adults, children, adolescents, healthy older adults, impulsive prisoners, and medical populations (with the exception of multiple sclerosis). However, more good-quality studies that evaluate the efficacy of Hatha yoga’s effects on EF are essential to build on this evidence base. Introduction disorder.3 In more recent years, interest has shifted from merely investigating Hatha yoga from a direct psychiatric oga is an ancient Indian practice designed to ‘‘still standpoint to also include examination of Hatha yoga’s ef- Ythe fluctuations of the mind’’ and facilitate meditative fects on cognitive functions, such as attention, concentra- absorption, a psychological state marked by feelings of self- tion, memory, and executive function (EF).4 transcendence and unceasing happiness.1 The most common For the past two decades, emerging evidence has sug- style of yoga practiced in Western countries is Hatha yoga, gested that Hatha yoga may indeed enhance EF. EFs are a which includes synchronized movements through postures set of higher-order cognitive processes that enable top-down with breath, meditation, breathing exercises, and supine rest (i.e., non–stimulus driven) control over behavior, emotion, to conclude.2 Examples of Hatha yoga include Ashtanga and thought; they most typically involve inhibitory control, yoga, Iyengar yoga, and yin/yang yoga. working memory, and mental flexibility, arising from the As an integrative mind-body practice, much research has operation of the prefrontal cortex and other closely con- accumulated regarding improvements in emotion-regulation nected centers.5 Other cognitive functions, such as attention following Hatha yoga practice. An overview study of meta- control, decision making, planning, and problem solving, analytic, systematic, and narrative reviews concluded that are often also classified as EFs because they are highly Hatha yoga is moderately beneficial in the context of re- correlated with EF or are functionally dependent on them.6 lieving anxiety and depressive disorders and conjunctively Although reviewers have discussed the effects of seated supporting standard treatments for post-traumatic stress meditation on cognition and EF,7–10 a comprehensive review 1Faculty of Applied Health Sciences, University of Waterloo, Waterloo, Ontario, Canada. 2Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada. 125 126 LUU AND HALL of Hatha yoga as a whole (i.e., yoga inclusive of meditation toring (OM).9 FA meditation consists of directing awareness plus physical posturing) has yet to be undertaken. The pur- to a chosen object, detecting distractions as they arise, and pose of this systematic review is to summarize the effects of subsequently redirecting awareness to the chosen object.9 Hatha yoga on EF. This review addressed the question: Does OM meditation, commonly known as ‘‘mindfulness,’’ in- Hatha yoga have beneficial effects on EF? For the purposes of volves sustained metacognitive awareness of internal and this review, an ‘‘acute bout’’ of Hatha yoga refers to a single external experiences, such as emotion, thought, and sensory practice session, ‘‘short-term training’’ refers to 1 week–6 stimuli, without attaching judgment or further explanation months of regular practice, while ‘‘long-term’’ training refers of their occurrence.28 Raghavendra and Telles29 found that to more than 6 months of regular practice. an acute bout of FA meditation improved attention and Given that Hatha yoga involves three main components— concentration task performance, while MacLean et al.30 physical activity, meditation, and breathing exercises—the found that 3 months of intensive FA meditation training literature pertaining to each of these components is first significantly improved vigilance during a visual attention reviewed in turn. In the context of Hatha yoga, aerobic and task in novice meditators. However, one systematic review resistance exercise is manifest in the form of continuous critically examined transcendental meditation, a form of FA movements through postures that stretch and strengthen the meditation that asks the practitioner to allow the mind to body; meditation and breathing exercises are integrated into wander but simultaneously concentrate on repeated mantras Hatha yoga practices both independently and in concert with and sound vibrations, and found that transcendental medi- movement. tation does not seem to improve cognitive functions.7 On the other hand, evidence suggests that OM training Physical activity improves attention28 and working memory31,32 while de- creasing mind-wandering.32 Experienced OM meditators Enhancements in EF after aerobic exercise have been well show significantly superior inhibitory control and selective established. For instance, acute bouts of aerobic exercise attention compared to meditation-naive controls.33 Moreover, improve inhibitory control,11–13 working memory,14 and studies analyzing brain scans of meditators who practice both planning,15 while one meta-analysis supports the positive FA and OM meditation found thicker brain regions in Brod- effects of exercise on EF.16 Some studies have documented mann areas 9/10 of the prefrontal cortex, right anterior insula, structural and physiologic brain changes associated with en- somatosensory cortex, and auditory cortex; areas associated hanced cognition following aerobic training. For example, an with attention, interoception, and sensory processing;34 and intervention study found increases in gray matter volume in the right orbito-frontal cortex and right hippocampus, asso- frontal regions of the brain among older adults after aerobic ciated with emotion regulation and response control.35 exercise training.17 Furthermore, a recent review by Erickson et al.18 concluded that more fit children and older adults tend Breathing exercises to exhibit greater hippocampal and basal ganglia volumes, greater white matter integrity, and superior performance on Studies investigating the effects of breathing exercises on cognitive tasks. Another systematic review revealed increases EF reveal mixed results. For instance, Telles et al.36 found in serum and plasma levels of brain-derived neurotrophic improvements in selective attention and concentration imme- factor, a neurotrophin that supports physiologic mechanisms diately after kapalabhati, a high-frequency forceful exhalation involved in neuroplasticity after acute bouts of aerobic ex- breathing exercise, in groups of medical students, middle-aged ercise;19 other studies involving animal models have docu- adults, and older adults. Conversely, Pradhan37 found no sig- mented enhanced localized glycogen storage in the cortex of nificant changes in working memory and selective attention rats after acute aerobic training.20 following kapalabhati breathing. Another study assessed three Although results are mixed, many studies have begun to breathing exercises: alternate-nostril breathing, where each support EF-enhancing abilities of resistance training. For nostril is alternately plugged by the index finger and thumb as example, studies have found significant improvements in so inhales flow through one nostril and exhales flow out inhibitory control21 and planning,22 but not working memo- through the other per breath cycle; right-nostril breathing, ry,23 after short-term bouts of resistance training in healthy where the left-nostril is plugged; and left nostril breathing, adults. Investigators report significant improvements in where the right nostril is plugged.38 Attention improved after working memory24 and inhibitory control25 after 6 months of the right- and alternate-nostril breathing exercises.38 Finally, resistance training, while inhibitory control significantly im- Telles et al.39 found increases in peak amplitudes and de- proved