Brain Plasticity xx (20xx) x–xxDOI 10.3233/BPL-190084IOS Press
1
Yoga Effects on Brain Health: A SystematicReview of the Current Literature
1
2
Neha P. Gothea,∗, Imadh Khana, Jessica Hayesb, Emily Erlenbacha and Jessica S. Damoiseauxb3
aDepartment of Kinesiology and Community Health, University of Illinois at Urbana Champaign4
bDepartment of Psychology and Institute of Gerontology, Wayne State University5
Abstract. Yoga is the most popular complementary health approach practiced by adults in the United States. It is an ancientmind and body practice with origins in Indian philosophy. Yoga combines physical postures, rhythmic breathing and meditativeexercise to offer the practitioners a unique holistic mind-body experience. While the health benefits of physical exercise arewell established, in recent years, the active attentional component of breathing and meditation practice has garnered interestamong exercise neuroscientists. As the scientific evidence for the physical and mental health benefits of yoga continues togrow, this article aims to summarize the current knowledge of yoga practice and its documented positive effects for brainstructure and function, as assessed with MRI, fMRI, and SPECT. We reviewed 11 studies examining the effects of yogapractice on the brain structures, function and cerebral blood flow. Collectively, the studies demonstrate a positive effect ofyoga practice on the structure and/or function of the hippocampus, amygdala, prefrontal cortex, cingulate cortex and brainnetworks including the default mode network (DMN). The studies offer promising early evidence that behavioral interventionslike yoga may hold promise to mitigate age-related and neurodegenerative declines as many of the regions identified areknown to demonstrate significant age-related atrophy.
6
7
8
9
10
11
12
13
14
15
16
17
Keywords: Cognition, brain, yoga review18
INTRODUCTION19
The practice of yoga dates back over 2000 years to20
ancient India, with a focus on the unification of the21
mind, body, and spirit through the practice of phys-22
ical movements, meditation and breathing exercises.23
Over the course of its lengthy existence, many dif-24
ferent schools of yoga have emerged, each placing a25
different emphasis on the practice. However, despite26
their different philosophies and combinations of exer-27
cises, they all are integrated in the common theme28
of uniting the mind and body. Yoga’s prominence in29
western civilization emerged in the late 20th century.30
Although a review of the PubMed search on yoga31
yields the earliest scientific studies dating to 1948,
∗Correspondence to: Dr. Neha P. Gothe, Kinesiology andCommunity Health, University of Illinois at Urbana Cham-paign, Urbana, IL – 61801. Tel.: +1 217 300 6183; E-mail:[email protected].
there has been an exponential increase in publica- 32
tions beginning in the 2000s (see Fig. 1). While its 33
origins root from religious principles, modern day 34
culture is primarily drawn to it for its relaxation 35
benefits (meditation and breathing exercises) and 36
stretching and strengthening movements (physical 37
poses). According to the National Center for Comple- 38
mentary and Integrative Health (NCCIH), yoga is the 39
most popular form of complementary therapy prac- 40
ticed by more than 13 million adults, with 58% of 41
adults citing maintenance of health and well-being 42
as their reason for practice [1]. One of the reasons 43
for yoga’s increase in popularity is its versatility, in 44
that it can be taught at a range of different intensi- 45
ties. A systematic review by Larson-Meyer examined 46
[2] the metabolic energy expenditure during Hatha 47
yoga, the most widely practiced style of yoga in the 48
United States. The review found that, while some spe- 49
cific yoga poses can be metabolically exerting (with 50
energy expenditures >3 METS), most yoga practices 51
2 N.P. Gothe et al. / Yoga Effects on Brain Health
Fig. 1. Search results from PubMed featuring the term “yoga” inthe title and/or abstract of publications over the years shows anexponential growth in yoga research beginning in the 2000s.
fall under the American College of Sport Medicine’s52
criteria of “light-intensity physical activity” (2–2.953
METS) [3]. Compared to traditional forms of aero-54
bic and anaerobic exercise, the relatively low-impact,55
modifiable nature of yoga can offer a middle ground56
for individuals with movement limitations, clinical57
diagnoses, and is particularly suitable for aging pop-58
ulations. Yoga’s focus on improving the self through59
both physical and mental practices incorporates more60
mindful elements absent in traditional forms of exer-61
cise.62
Indeed, the practice of engaging the mind and body63
through meditation, breathing and physical poses has64
attracted significant attention from the medical com-65
munity, and yoga has been frequently studied for its66
possible beneficial effects on physical and mental67
health outcomes. Systemic and meta-analytic reviews68
of randomized control trials have found positive69
associations between yoga practice and improve-70
ments in diabetes [4, 5], cardiovascular function [6],71
and musculoskeletal conditions [2, 3]. There is also72
considerable evidence for the beneficial effects of73
yoga practice on mental health including anxiety [9],74
stress [10, 11] depression [12, 13] and overall men-75
tal health [14]. Typically, yoga has been studied as76
an adjunct therapy in these studies conducted with77
adults and older adults often with clinical diagnoses.78
For example, Lin and colleagues [15] conducted a79
meta-analysis assessing the effects of yoga on psy-80
chological health, quality of life, and physical health81
of patients with cancer. They concluded that the yoga82
groups showed significantly greater improvements in83
psychological health, as indicated by anxiety, depres-84
sion, distress, and stress levels, when compared with85
the waitlist or supportive groups.86
Yoga’s acute and intervention effects on cogni-87
tion are evident in a recent meta-analysis [16] which88
reported moderate effect sizes for attention, pro- 89
cessing speed and executive function measures for 90
studies conducted with adult populations. Yoga prac- 91
tice enables the practitioner to move in a controlled 92
manner into modifiable physical postures concen- 93
trating initially on relaxing their body, breathing 94
rhythmically, and developing awareness of the sen- 95
sations in their body and thoughts in their mind. In 96
addition to the physical benefits from sequentially 97
completing the postures, the breathing (pranayama) 98
and meditation exercises included in yoga are prac- 99
ticed to calm and focus the mind and develop 100
greater self-awareness [17]. It is hypothesized that 101
this combination of metacognitive thought and bodily 102
proprioception during yoga practice could general- 103
ize to conventionally assessed cognitive functions 104
including attention, memory, and higher-order exec- 105
utive functions. However, it is currently unknown if 106
this relationship exists as a direct pathway, or if yoga 107
indirectly influences cognitive functions through pro- 108
cesses such as affective regulation. Negative affect 109
including depression and stress are known to detri- 110
mentally impact both cognitive functioning [18] and 111
brain structure [19] and systematic reviews discussed 112
earlier have demonstrated the potential of yoga to 113
improve anxiety, depression, stress and overall men- 114
tal health. 115
Yoga has particularly gained traction as a research 116
area of interest in its promising potential as a therapy 117
to combat the alarming increase in age-related neu- 118
rodegenerative diseases. Older adults are the fastest 119
growing population in the US and around the world 120
with over 2 billion people expected to be ≥60 years 121
of age by 2050 [20]. Age is the biggest risk factor 122
for Alzheimer’s disease, the most common cause of 123
dementia in those aged 65 and older. In the absence of 124
any effective treatments to cure the disease or manage 125
its symptoms, researchers have explored the poten- 126
tial of modifying lifestyle behaviors such as nutrition 127
and physical activity to drive beneficial plasticity of 128
the aging brain and remediate age-related cognitive 129
decline. Yoga may be an alternative form of physical 130
activity which may help not only older adults achieve 131
recommended levels of physical activity, but also for 132
individuals who have disabilities or symptoms that 133
prevent them from performing more vigorous forms 134
of exercise. 135
The purpose of this review was to synthesize the 136
current evidence for yoga’s effect on brain structure 137
and function among adults and identify the regions 138
and neural networks impacted by its short-term or 139
long-term practice. 140
Unc
orre
cted
Aut
hor P
roof
N.P. Gothe et al. / Yoga Effects on Brain Health 3
METHODS141
Literature search and study selection142
The aim of this review was to examine the role143
of ‘holistic’ yoga practice, i.e. studies that explored144
the role of yoga practice which included each of its145
three elements: yoga postures, yoga-based breath-146
ing exercise and yoga-based meditative exercises. We147
used the following databases to identify studies from148
inception to July 2019 that have examined effects149
of yoga on brain health: MEDLINE, PsychINFO,150
PubMed, Indian Council of Medical Research, and151
Cochrane. We used the following a priori search terms152
to identify all the relevant published articles: ‘yoga’,153
‘hatha yoga’ and ‘brain health’, ‘brain function’,154
Lower dorsolateralprefrontal cortex(dlPFC) activityduring encodingphase of workingmemory taskamong yoga experts
Afonso (2017) N = 42; olderadults – 21experts and 21controls; 67.05years; 0 : 21
Hatha Cross-sectional 8+ years of yogaexperience vs.no yoga ormindfulnessexperience
MRI Greater corticalthickness in leftprefrontal loberegion, includinglateral middlefrontal gyrus,anterior and dorsalsuperior frontalgyrus among yogaexperts
Yang (2016) N = 25, healthyolder adultswith MCI – 14randomized toyogicmeditation and11 to memoryenhancementtraining; 67.4years; 13 : 12
6 N.P. Gothe et al. / Yoga Effects on Brain Health
Table 1(Continued)
Study author Sample size; Style of Yoga Study design Categorization Imaging Study findings(Year) characteristics; of Yoga methodology
Mean Age; Group/practitionerMale:Female and controls
Villemure (2015) N = 28; healthyadults – 14 yogaexperts and 14controls; 36.85years; 10 : 18
All types (thatintegratedphysicalpostures, breathcontrolexercises andmeditation.)
Cross-sectional No definedcriteria,open-endedquestions todetermine yogaexpertiseresulting inaverage yogaexperiencerange of 6–16years
MRI No correlationbetween age andwhole-brain totalGM volume amongyoga experts(negativecorrelation incontrols)
Positive correlationbetween years ofyoga practice andGM volume in leftmid-insula, leftfrontal operculum,left orbitofrontalcortex and rightmiddle temporalgyrus
Positive correlationbetween weeklyhours of practiceand GM volume inright primarysomatosensorycortex and superiorparietal lobe, lefthippocampus,midlineprecuneus/posteriorcingulate cortices,and right primaryvisual cortex
Negative correlationbetween cognitivefailures and GMvolume
Positive correlationbetween years ofyoga experienceand GM volume
Froeliger (2012a) N = 14; healthyadults – 7 yogaexperts and 7controls; 35.95years; 2 : 12
Hatha Cross-sectional 3+ years of yogaexperience with45 + min ofpractice 3-4times per weekvs no yoga ormeditationexperience
Task-basedfMRI
Lower right dorsallateral prefrontalcortex (i.e. MFG)activity duringviewing of negativeand neutralemotional imagesamong yoga experts
Greater left superiorfrontal gyrusactivity duringStroop task amongcontrols
Greater leftventrolateralprefrontal cortexactivity duringStroop task withpresence of negativeemotionaldistractors thanneutral emotionaldistractors in yogaexperts (oppositepattern for controls)
No correlationbetween amygdalaactivation toviewing negativeemotional imageand task-relatedchanges in affectamong yoga experts(decreases inpositive affect werecorrelated withincreased amygdalaactivation incontrols).
(Continued)
Unc
orre
cted
Aut
hor P
roof
8 N.P. Gothe et al. / Yoga Effects on Brain Health
Table 1(Continued)
Study author Sample size; Style of Yoga Study design Categorization Imaging Study findings(Year) characteristics; of Yoga methodology
Mean Age; Group/practitionerMale:Female and controls
Decrease in averagecerebral blood flowratio in rightamygdala, rightdorsal medialcortex, and rightsensorimotor areaduring baselinescan following yogaintervention
Greater activity in theleft side of anteriorcingulate,dorsomedial frontalcortex, superiortemporal loberelative to the rightfollowing yogaintervention
Greater lateralitypreference for theleft over the righthemisphere duringmeditationcompared tobaseline followingyoga intervention
vidual who had consistently practiced yoga for at least216
3 years on a weekly basis.217
Effects of yoga practice on brain structure218
In order to identify the effects of yoga practice219
on brain structure, researchers have utilized MRI220
to investigate how the structure of the brain differs221
among those with experience practicing yoga (see222
Fig. 3).
Cross-sectional studies examining group 223
differences 224
The majority of these studies have relied on 225
comparing the brain structure of experienced yoga 226
practitioners, with the brain structure of non- 227
practitioners, or yoga-naıve controls, to detect 228
cross-sectional differences existing between the 229
groups. Afonso et al. [23] found differences in cor- 230
tical thickness among female adults over the age of 231
60 with 8 or more years of Hatha yoga experience 232
compared to a non-practitioner control group. The 233
Unc
orre
cted
Aut
hor P
roof
N.P. Gothe et al. / Yoga Effects on Brain Health 9
Fig. 3. Brain regions showing A) structural differences in yoga-practitioners compared to non-practitioners or B) a dose-dependent rela-tionship between years of yoga practice and brain structure among practitioners. Yoga practitioners exhibited greater cortical thickness,gray matter (GM) volume, and GM density than non-practitioners in a variety of regions. Among yoga-practitioners, a positive relationshipbetween the years of yoga practice and GM volume was also observed in a number of areas. All but one of the regions shown were createdby making a 5 mm sphere around the coordinates provided in the studies reviewed. Since Gothe et al. (2018) did not investigate volumedifferences on a voxel-wise basis, a mask of the whole structure is shown.
during the encoding phase of a working memory task 673
in comparison to the controls. Froelinger et al. [30] 674
also found yoga practitioners to be less reactive in the 675
right dlPFC when viewing the negatively valanced 676
images on the affective Stroop task. Task-relevant 677
Fig. 4. Brain regions showing differential task-related activationin yoga-practitioners. Yoga practitioners showed less activationthan non-practitioners in the left dorsolateral prefrontal cortexduring the encoding phase of a Sternberg Working Memory task(yellow). Yoga practitioners also showed less activation than non-practitioners in the right dorsolateral prefrontal cortex and rightsuperior frontal gyri, but more activation in the left ventrolateralprefrontal cortex during various aspects of an Affective Stroop task(red). All regions shown were created by making a 5 mm spherearound the coordinates provided in the studies reviewed.
Unc
orre
cted
Aut
hor P
roof
14 N.P. Gothe et al. / Yoga Effects on Brain Health
targets activate the dlPFC, whereas emotional distrac-678
tors activate the amygdala [49]. Exerting cognitive679
control over emotional processes leads to increased680
activation in the dlPFC, with corresponding recipro-681
cal deactivation in the amygdala [50, 51]. The studies682
suggest that when emotional experience occurred683
within the context of a demanding task situation,684
yoga practitioners appeared to resolve emotional685
interference via recruitment of regions of the cor-686
tex that subserve cognitive control. Plausibly, these687
findings may indicate that yoga practitioners selec-688
tively recruit neurocognitive resources to disengage689
from negative emotional information processing and690
engage the cognitive demands presented by working691
memory and inhibitory control tasks demonstrating692
overall neurocognitive resource efficiency.693
A network of neural structures including the694
frontal lobe, the anterior cingulate cortex, the infero-695
temporal lobe and the parietal cortex are known to be696
involved in cognitive operations including stimulus697
processing and memory updating [52, 53]. Specif-698
ically, the anterior cingulate cortex is part of the699
brain’s limbic system and has connections with mul-700
tiple brain structures that process sensory, motor,701
emotional and cognitive information [54]. In our702
reviewed studies, Eyre et al. [32] found verbal mem-703
ory performance to be correlated with increased704
connectivity between the pregenual anterior cingu-705
late cortex, frontal medial cortex, posterior cingulate706
cortex, middle frontal gyrus, and lateral occipital cor-707
tex following a 12-week yoga intervention. Villemure708
et al. [26] also reported a positive correlation between709
the dose of weekly yoga practice and GM in the cin-710
gulate cortex. Collectively these results are promising711
and corroborate the aerobic exercise literature, as the712
anterior cingulate cortex is one of the brain struc-713
tures that shows disproportional changes as a result714
of participation in moderate intensity physical activ-715
ity [55]. Many of these regions are part of the default716
mode network, which is typically activated during717
rest and deactivated when an individual is engaged718
in an external task [56]. Following a yoga interven-719
tion, increases in connectivity of regions in the DMN720
were associated with improvements in verbal mem-721
ory recall [32]. Given that functional connectivity of722
the DMN has been negatively associated with age-723
related pathologies such as Alzheimer’s disease [57],724
as well as in the context of typical aging [58], the725
increases in functional connectivity in regions of the726
DMN reported by Eyre et al. further indicate that yoga727
practice is a promising intervention for use among728
aging populations.729
Future directions 730
Although yoga-cognition has emerged as a topical 731
area in the field of exercise neuroscience, the studies 732
are preliminary and lack the rigorous methodology 733
that is applied in the exercise-cognition literature. 734
Sample sizes for yoga studies have ranged from 4 735
to 102 participants and a majority of the work has 736
been cross-sectional in nature. While the beauty of 737
yoga lies in the diverse and modifiable combinations 738
of postures, breathing and meditative exercises, this 739
concurrently poses a challenge for scientists to com- 740
pare findings across studies. Furthermore, there is no 741
standardized definition for a yoga practitioner, nor 742
a universal standard for certification. Of the yoga 743
practitioners sampled in the reviewed studies, their 744
experience ranged from regular practice 3–5 days a 745
week for 3 to 16 years. This poses a challenge to 746
compare research findings across studies. 747
Although cross-sectional studies limit us in our 748
ability to draw casual conclusions, such a design 749
can provide certain advantages over the use of inter- 750
ventional studies design in identifying the effects of 751
yoga practice on the brain given that 9.3 years was 752
the lowest average number of years of yoga prac- 753
tice reported by yoga-practitioners in these studies. 754
Following yoga-practitioners for such an extended 755
period in an intervention design would pose a variety 756
of practical difficulties, and thus cross-sectional com- 757
parisons between yoga practitioners and yoga-naıve 758
controls provide a unique opportunity to gain an idea 759
of the maximal benefits that extensive yoga practice 760
may lead to. Nonetheless, it is the promise of yoga 761
as an intervention for individuals with various health 762
issues that has sparked much of the growing interest 763
in the effects of yoga practice on brain structure and 764
function, since its established cognitive benefits and 765
accessibility to people with a wide range of physical 766
capabilities suggest it may be an effective interven- 767
tion for typical and pathological cognitive decline 768
among older adults. Yet for yoga interventions to 769
have clinical utility in such circumstances, compli- 770
ance to the intervention program is a necessity. None 771
of the reviewed intervention studies provided infor- 772
mation about participants’ compliance and adherence 773
to the yoga program. Future studies need to document 774
and report attendance and adherence rates. The inter- 775
vention studies also employed different frequencies, 776
intensities and doses of yoga practice which resulted 777
in heterogeneity across intervention designs as well. 778
While the reviewed studies examined the relation- 779
ship between yoga and brain structure or function, 780
Unc
orre
cted
Aut
hor P
roof
N.P. Gothe et al. / Yoga Effects on Brain Health 15
only one [24] employed cognitive or behavioral781
assessments which correlate with the studied brain782
regions. Future studies should administer such assess-783
ments to establish if the neural changes produced by784
yoga practice are indeed manifested into improved785
