|
 
 |
| REVIEW ARTICLE |
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| Year : 2020 | Volume
: 4
| Issue : 2 | Page : 33-39 |
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Yoga and brain wave coherence: A systematic review for brain function improvement
Anup De, Samiran Mondal
Department of Physical Education and Sport Science, Visva-Bharati University, Santiniketan, West Bengal, India
| Date of Submission | 26-Nov-2019 |
| Date of Acceptance | 29-May-2020 |
| Date of Web Publication | 13-Jul-2020 |
Correspondence Address:
Mr. Anup De
Research Scholar, Department of Physical Education and Sport Science, Visva-Bharati University, Santiniketan, West Bengal
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/hm.hm_78_19
Background: The recent hype in yoga practice is concomitant with the fact that it helps the practitioner to achieve radiant health and serene mind. The science of yoga has also become a powerful stream of knowledge. It has increased the number of scientific studies on different yogic interventions, but has also been performed to evaluate its effects on brain wave activity, particularly in neural oscillations. Objectives: In this systematic analysis, we reviewed studies investigating the effect of integrated yoga, meditation, and pranayama on brain wave activity that affects overall cognitive functions. Methods: Broad search strategy was practiced using several online databases: PubMed, Google Scholar, Web of Science, Embase, Medline, PsycINFO, Europe PMC, Scopus, and IndMED. Studies were included in integrated yoga, meditation, and pranayama with brain wave activity, and the entire relevant articles were critically analyzed according to the nature of this study. Results: Several studies examined yogic interventions for restoring brain functions, nerve diseases, and cognitive impairment and suggested that integrated yoga, meditation, and pranayama practices improve verbal skills, reaction time, hand–eye coordination, speed accuracy, and neural activity. Yogic intervention increases overall brain wave (delta, theta, alpha, beta, and gamma) activity, which increases overall cognitive functions with greater perceived cognition, working memory, attention, better switching ability, focusing ability, positive mind, and perception. It has also been reported that yogic intervention activates dormant areas of brain while downgrading memories not of interest and upgrading useful ones.Conclusions: There is emerging evidence from randomized controlled trials to support yoga practice, which significantly improves brain wave activity resulting in better cognitive functions.
Keywords: Asana, brain waves, cognitive functions, integrated yoga, kriya, meditation, mudra, pranayama, yoga
How to cite this article:
De A, Mondal S. Yoga and brain wave coherence: A systematic review for brain function improvement. Heart Mind 2020;4:33-9 |
| Introduction | |  |
The science of yoga is a powerful vehicle of knowledge, which enables the practitioners to achieve radiant physical health, serene mind, and continuous spiritual uplift and creates the ability for better harmony in social living.[1] The ancient traditional texts described different elements of yoga called the eight steps of yoga, i.e., yama (self-restraints), niyama (self-observances), asana (posture), pranayama (breathing control), pratyahara (disassociation of consciousness from the outside environment), dharana (concentration), dhyana (meditation), and samadhi (identification with pure consciousness).[2],[3] Comprehensive yogic interventions, including meditation, pranayama, and asana, have become more popular, and increasing numbers of scientific studies have been performed to evaluate their effect on brain wave activity, particularly in neural oscillations. The recent increased interest in this ancient mental practice is concomitant with the development of new brain imaging technologies as well as the incorporation of yoga. It is one of the core psychological components of these practices into psychotherapeutic and clinical interventions.[4] It has been established that emotions, behaviors, and other psychological states comprise the roots of thought process impact in the brain waves.[5]
In the brain, there are millions of neurons, each of which generates small electric voltage fields. The aggregate of these electric voltage fields creates an electrical reading, and electrodes on the scalp are able to detect and record electroencephalon (EEG) pattern.[6] Synchronizations of electrical pulses from masses of neurons in the brain which communicate with each other are called brain waves. The frequency of the brain wave activity alters according to the state of consciousness and state of mind of the individuals. Beta activity is normally noted in the awake working state. Alpha activity that goes on into different stages of sleep may change into theta and may also exhibit delta activity in deep sleep.[7] Whereas, alpha and theta waves are attributed to be responsible for concentration, relaxation, and overall health issue. The delta and beta wave domination causes elevation in blood sugar level, which causes hyperglycemia, weight gain, uneasiness, and anxiety.[5],[8] Alpha waves occur during moderate levels of brain activity, while an individual is temporarily idle, but alert. It is found within the cortex, occipital lobe, and thalamic region of the brain, and it occurs during a sleeping or drowsy state.[9],[10] In addition, alpha wave which occurs whenever a person is alert but not actively processing information is strongest over the occipital cortex and also over the frontal cortex that is linked to extroversion and creativity.[7] Scientists have reported that alpha wave is inhibited to the areas of cortex and plays a vital role in networking among neurons.[11] It may improve word recognition in older adults as well as facilitate working memory, cognitive benefits, that is associated with an increased and better perception and calmness.[9],[10] Alpha production promotes a mental resourcefulness, aids in the ability to mentally coordinate, and enhances the overall sense of relaxation and fatigue.[7] Beta waves occur during a heightened state of awareness, and this state is a type of brain oscillation that is reflected as a task is being completed, and throughout active concentration. Beta waves are also predominantly present throughout the motor cortex during isotonic contractions and slow movements.[12],[13],[14] Beta wave directly affects mood and emotions and significantly decreases emotional exhaustion and state anxiety.[12] Beta wave indicates that the person is in normal waking consciousness, delta wave signifies deep sleep, and theta indicates that the person is in a state of extreme relaxation.[15] Theta wave may occur in both cortical and hippocampal regions of brain.[16] Basically, gamma wave originates from the thalamus, and it moves anteriorly and activates synchronization of neuronal activity establishing neuronal circuitry,[9] that is associated with enhanced attention and neural activation.[4] Gamma wave patterns of high-frequency brainwaves are also found in every part of the brain and relate the performance of higher mental activities and perceptual tasks.[17]
As the field of yoga and brain research is very much emerging in a progressive way, the purpose of this study is to provide a broad overview of the attempts to investigate the effect of yogic practice on brain wave activity that affects overall cognitive functions.
| Methods | | |
Study search and selection
Studies were identified by searching the databases PubMed, Google Scholar, Web of Science, Embase, Medline, PsycINFO, Europe PMC, Scopus, and IndMED without any restrictions. To avoid excluding potentialities relevant to articles at the search stage, a relatively broad search strategy was used, so all the studies on the effect of yoga on brain waves were identified. The query: brain waves AND yoga OR meditation OR pranayama OR cognitive functions were used in the topic field of electronic databases. The search was not restricted to include only “brain waves” or related search terms, as we also wanted to identify studies that did not primarily focus on brain waves but still included some measures of it. In addition to database searches, additional relevant studies were identified from the reference lists of the examined articles. When the full texts were not available, attempts were made to contact the corresponding author or other subscription sources. If a reply was not received, abstracts were read properly to check if they had the required information.
Eligibility criteria
Eligibility of articles was assessed on the basis of eligibility criteria first at the level of the title, abstract, and source, and then the full-text articles. Original studies of all designs investigating the effect of yogic intervention on brain wave activity that may enhance cognitive flexibility in the context of brain function were eligible. After collecting articles, the researcher confirmed literature surveys with three categories, namely integrated yoga, meditation, pranayama, with the brain wave activity. Whereas studies which were not of direct match with the concept of analysis or did not include yoga as an intervention were excluded from the procedure. Full-text reading of articles that were potentially eligible was undertaken. The schematic representation of the literature survey is shown in [Figure 1].
| Results | | |
After the exhaustive search and selecting the studies on the basis of inclusion criteria, 73 articles were shortlisted for systematic review. All the selected studies were only experimental with yogic interventions. The data synthesis was done by categorizing the study findings under brain wave activity with the interventions of integrated yoga (n = 20), meditation (n = 38), and pranayama (n = 15). All the studies' findings suggest that yogic interventions including integrated yoga, meditation, and pranayama enhance the brain wave activity in different modes and methods that positively correlates with cognitive functions. The studies were limited and summarized using a narrative approach and hence meta-analysis could not be done. The data extractions included the interpretation performed and findings of the research outcomes.
Integrated yoga alters the brain wave coherence
Nowadays, yoga acts as an alternative therapy or medicine for the improvement of brain functions. Several scientists applied yogic intervention for reducing brain disorder, nerve diseases, and cognitive impairments. Yogic intervention increases the alpha, beta, and delta band power in frontal, central, parietal, occipital, and temporal lobes, while, it increases theta band power only in occipital lobe and gamma band power in frontal and slightly in temporal lobes.[18] Basically, the frontal lobe functions with reasoning, planning, problem-solving, and cognition, whereas the parietal lobe is associated with visual perception, recognition, information processing, and spatial reasoning, the temporal lobe is linked with memory and processing of verbal and auditory signals, and the occipital lobe with visual spatial processing and recognition.[18] Scientists found 19.31% increase in delta, 5.04% increase in theta, 15.40% increase in alpha, and 18.68% increase in gamma wave coherence, while beta wave decreases in 1.67% after yoga practices.[19] Asana, pranayama, and meditation practices activate the alpha, beta, and theta waves that influence perception, memory, and mood.[20] Whereas researchers reported that yoga practice significantly increases in delta wave coherence, which is associated with higher states of consciousness, and increasing alpha wave coherence is found to influence the wakefulness and vigilance.[19],[21] Yoga may be a method for stimulating theta activity that is associated with benefitting anxiety and memory.[9] Kriya-based yoga practice showed a 40% increase in alpha and theta waves primarily in the parietal region.[9] Asana meditation practice increases the alpha and theta brain wave activities that reduce anxiety.[9],[22] Yoga meditation practice can also increase the frontal alpha coherence, which reflects an enhancement of frontal lobe integration that improves cognitive flexibility, intelligence, and emotional stability.[19] Scientists examined that yoga training program increases overall brain wave activity, which decreases anxiety and increases focusing ability.[9] Similarly, santhi kriya practice significantly increases the alpha activity.[23] In addition, super brain yoga also significantly improves the alpha wave score.[24] Yogic practices increase alpha wave activity in the occipital and prefrontal cortices in both hemispheres, which enhances better relaxation.[22] Asana pranayama practice significantly increases alpha wave activity during police training.[9] Two bouts of yoga pranayama practice helps to increase alpha and beta wave activation.[25] Scientists found that breathing, meditation, and asana-based yoga practices increase the alpha wave activity which is associated with better perception and calmness.[9] Alpha wave increases the relaxed state of mind and its band power is inversely connected to mental activity.[18] Beta wave increases cognitive skills after yoga session.[9] Researchers found that yoga and pranayama training may increase the beta activity that subsequently reduces the emotional exhaustion, state anxiety, and fatigue.[9] Scientists also examined that yogic intervention increases occipital gamma power that is related with enhanced sensory awareness.[19],[26] Alternatively, absence of gamma wave may be the result of thalamic injury that can make any individual slip into profound coma.[12] Yoga can increase the gray matter volumes in temporal and frontal lobes, which produces positive impacts on mental health and improves overall cognitive functions. It has also been suggested that yoga practice can also bring improvement in tasks which are associated with selective attention, concentration,[1],[27],[28] visual processing capacity, and enhancement in sensory motor activity.[18],[29] Another scientist found that yoga practice increases gray matter along with increases in the amygdale and activates the frontal cortex that proportionately contributes to memory.[9] Similarly, long-term yoga practice can increase gray matter volume that acts as an alternative therapy for reducing neurological disorder.[30] Yoga practice improves autonomic flexibility by modulating parasympathetic dominance,[24],[31],[32],[33] and significant changes are found in sensory motor rhythm around the brain.[18],[34] Yoga helps to contribute the amygdale function and increases brain wave activity that is associated with increase in positive mood and perception.[9],[24] Integrated yoga including agnisara, nauli, and bhastrika practice changes the EEG pattern around the somatosensory and parietal areas of the cerebral cortex.[22],[35] Scientists are trying to test that yoga improves the central neural processing ability that may attribute to greater arousal and faster rate of information-processing ability.[22],[36]
Meditation alters the brain wave activity
The frequency of brain wave activity is altered according to the state of consciousness and state of mind during meditation.[37] The practice of yoga nidra is the intermediate stage of awakened and sleep, and this stage of the brain produces alpha waves. With the advancement of yogic intervention, beta activity is slowly replaced by alpha activity and still further by smooth well-formed alpha activity.[37] Scientists found that shambhavi maha mudra practice highly increases the delta and theta band power and markedly decreases beta band power throughout the EEG spectrum.[38] Whereas, zen meditation practice activates the anterior cingulate cortex that elicits theta rhythm, which has a positive effect on cognitive and affective processes. While, midline theta is also seen to induce relaxed concentration and enhanced interaction between cognitive and affective processes.[39],[40] Researchers observed increases of slow alpha in intermediate meditators, while advanced yoga meditators showed emergence of rhythmic theta waves.[41] Yoga meditation practice increases the alpha activity.[41] Scientists examined that yoga meditation practice increases the alpha and beta values around 90% practitioners, that reflects extreme relaxation state which increases alertness to the external world.[15] Nadabrahma meditation practice significantly increases alpha wave which reduces stress and anxiety.[42] High alpha frequency is mainly associated with centering and healing with mind–body connection, whereas beta wave physiologically correlates alertness and activeness and helps with general activation for mind and body functions.[43] Meditation practice increases alpha and theta power,[6],[44] while higher alpha power is also found after vipassana meditation practice.[4] Similarly, sudarshana kriya practice also increases the alpha band.[45] Nondirective meditation practice increases the alpha and theta waves, and it paves way for relief of stress, increasing memory and more concentration in this modern lifestyle.[5] Mindfulness meditation practice increases the alpha activity especially in frontal regions.[40],[46] The theta and alpha waves are found greater during mindfulness meditation,[47],[48] which reflects lower tonic arousal and a state of relaxed and alertness in frontal regions.[40],[49] Meditation practice significantly increases low-frequency alpha and theta activities that inhibit cortical processing, which is reflected on external sensory and motor processing performance.[48] Transcendental meditation practice increases the frontal and central alpha activities which are associated with wakefulness,[50] cognitive flexibility,[36] and mind–body coordination.[1],[51] Higher frequency of gamma activation (>30 Hz) is specifically associated with meditative state.[4],[52] Tibetan Buddhist meditation practice increases gamma power (25 ± 40 Hz) over the parieto-occipital areas.[53] Meditation practice activates higher gamma synchronization in frontal areas.[4] It was examined by another researcher that meditation practice is associated with greater activity in high-frequency beta and specially gamma waves.[48] Several researchers studied on Tibetan Buddhist monks' meditation practice and found increased gamma activity in the right mid temporal gyrus.[48],[52],[54] Scientists also examined that 10 years' practice of advanced Western vipassana meditation significantly increases gamma power in parieto-occipital electrodes.[26] Basically, meditation practice activates the cingulate gyrus, thalamus, and orbital and inferior frontal cortices.[55],[56] Volitional meditation practice increases the activity of prefrontal cortical areas, which is attributed to cognitive performance,[57] whereas vipassana meditation practice increases greater gray matter concentration in the brain.[58],[59] Meditation practice activates fiber integrity in pathways connecting to the hippocampus.[60] Meditation energizes the prefrontal lobes of the human brain that reflects in limbic system becoming harder to arouse.[1] Scientists reported that yoga nidra produces alpha dominance in the brain, which is characterized by mental relaxation.[7] Meditation practice increases frontal electrical coherence, which reflects an enhancement of frontal integration, cognitive flexibility, intelligence, and emotional stability.[38],[47] Rajyoga meditation practice activates the alpha and theta band oscillations that reduce the activity of multifunctional neuronal network which is related to attention, orientation, memory, and emotions.[40],[61],[62] Scientists tried to interpret the effect of meditation on subconscious mind effectively and found enhancing memory power.[63] Researchers reported that meditation can enhance various cognitive functions including attention, memory, verbal fluency, executive function, processing speed, and creativity, that positively affects brain functions.[52],[59],[64] Concentrative meditation practice improves the performance of perceptual rivalry and preattentive processing ability of attentional blink task.[36],[65] Long-term concentrative meditation significantly improves information-processing speed,[36] whereas OM meditation practice also improves mental alertness.[1],[66]
Pranayama alters the brain wave coherence
Pranayama increases both alpha and beta activities in the very beginning of the practice, which increases awareness and relaxation at a time. In day-to-day life, the beta activity decreases and alpha activity increases when the person is aware and awake with daily activities, and this pattern reverses when the person is relaxing and falling asleep.[67] Pranayama practice increases theta power that is associated with decreased activity in the brain arousal system and sleep onset process.[17],[68] Such practice improves the state of relaxation with reduced level of anxiety that is reflected by the presence of increased alpha band power and decreased beta band power. During such practice, it has been examined that the brain remains deeply focused with higher level of mental consciousness as indicated by the increase in delta and theta band powers.[67] Scientists reported that alternate nostril yoga breathing decreases theta band power over the right occipital region, while alpha and beta amplitudes also reduce at the right occipital site and the right vertex site of the brain.[69],[70] At the same time, nostril breathing practice also increases the spatial memory scores.[71] Two-month sheetali and sheetkari pranayama is beneficial to the body and mind as indicated by an increase in delta and alpha band power in the frontal and occipital regions and an increase in theta band power in the frontal region with a marked decrease in the beta band power almost throughout the entire hemisphere. It indicates that the brain is calm and quiet in relaxed state with less anxiety.[67] Pranayama practice produces alpha dominancy in the electrical pattern of brain, which is mainly associated with mental relaxation.[67] Scientists examined that nadi sodhan pranayama practice also increases alpha EEG band power in students. Pranayama practice increases the activity of alpha and beta powers that enhances relaxation and cognition and thus leads to a stress-free healthy life.[72],[73] Pranayama generates increased beta wave activity in the motor cortex,[70],[74],[75] and this activity increases alertness, arousal and excitement,[69] concentration, visual acuteness, and normal waking state of mind.[17] Pranakarshan pranayama alters the EEG brain wave patterns to the level of consciousness, while bhramari pranayama practice improvises the activity of the brain by generating high-frequency biphasic paroxysmal gamma waves.[7],[12],[67] Scientists found that pranayama helps to improve balances between right and left hemispheres of the brain that attribute to circulating neuropsychological functions.[17] Researchers also tried to focus that regular pranayama practice increases cognitive performance, bringing relaxation and improving spatial memory performances.[76] Regulation of breathing technique improves the performance of spatial memory, visual memory, and verbal memory.[77] The processing of sensory information in the thalamic level is facilitated during the practice of pranayama.[1],[78]
Yoga improves cognitive function
Yogic intervention increases cognitive performance and greater perceived cognition.[71] A study found that 6-week hatha yoga practice improves working memory and attention-switching ability in healthy older adults.[79] Yoga practice is particularly associated with increase in positive mood, short-term memory, and decreased pain perception.[9],[80] Yoga meditation practice improves various cognitive functions such as performance enhancement, neural activity, active attention, and executive functions.[18] Researchers are suggesting that integrated yoga including pranayama, asana, and meditation practice improves verbal skills, reaction time, hand–eye coordination,[80] speed, accuracy, and neural performances.[29],[81],[82] It has also been reported that yogic intervention develops memory, perception, and attention span and activates dormant areas of the brain, while replacing useless memories with useful ones.[77] Similarly, hatha yoga including asana, kriya, mudra, bandha, and meditation practice develops awareness, intellectual efficiency, and somatic functions.[1] Yoga meditation practice enhances the state of consciousness, mental activity, and the sense of well-being and responsiveness.[83] Hence, we may suggest that yoga can also enhance cognition and overall brain functions.[84]
| Discussion | | |
The effects of yogic interventions including integrated yoga, meditation, and pranayama are pronounced in the evidences obtained from the above findings. All the studies directly or indirectly have found yoga to be beneficial on brain wave activity. In the human body, brain is the supreme coordinator that regulates any kind of movements and functions. Electrical activity of the brain results in the emergence of new oscillations which indicate the state of mental function. Scientists correlated this electrical activity with the state of mental activity as an intervention of yoga. Increase of frontal theta band power indicates intellectual concentration and meditative state, that reduce nervousness and are negatively related with sympathetic activation.[85] Activation of theta wave reduces the anxiety, improves short-term memory, and influences the process of building memories.[16] Theta wave also provides heightened intuition, healing of body, and reprogramming of the subconscious mind.[86] While increase in beta band power indicates a higher level of alertness and enhanced engagement task and improvement in various cognitive abilities such as memory, attention, concentration, and reaction time,[83],[87] increase in alpha and delta power indicates synchronization of brain activity with greater alertness.[83] Arousal theory also suggests that increased beta activity is associated with increased mental activity or arousal,[88] and it occurs when a person is in attentive and active state of mind.[63] The beta signal physiologically correlates alert, active but does not agitate general activation of mind and bodily functions.[43] In addition, improvement of alpha power indicates greater mental silence, tasks requiring, memory and imagination,[89],[90] while high frequency of alpha is mainly associated with centering, healing, and improving mind/body connection.[43] Lower alpha band appears for vigilance and attention, whereas upper alpha band is thought to reflect task-specific processes, i.e., perceptual and cognitive processes.[91],[92] Alpha and theta can be interpreted as signifiers of increased attention, with alpha specifically representing internalized attention as well as indexing states of relaxation.[93] Delta wave is basically associated with the deepest state of consciousness,[38] whereas enhancing gamma power indicates higher level of awareness and consciousness, where our mind and body achieve a new emerging energy.
Many studies available are heterogeneous and are dealing in different grounds, and this heterogeneity serves as a resource for the limited scope of studies on yoga and brain wave research. However, there is a need to focus on strengthening the methodology and study designs for more valid and reliable results. Randomized controlled trials (RCT) are universally accepted as top rated study design due to their high degree of reproductivity. Hence, more RCTs are important in this field on the evidence of the effect of yoga and brain waves empirically.
| Conclusions | | |
This systematic review finds emerging scientific evidences to support a beneficial role of yoga for improvement of brain wave activity, which suggests better cognition, improved neuropsychological functions, and overall brain functions. Furthermore, yoga is positively correlated with brain wave activity, resilience, and global brain network efficiency. These findings reveal the possibility to increase mental resiliency and to make slow the decline of brain's functional architecture and suggest that yoga plays a mechanistic role for the improvement of brain activity.
Limitations
The present review may provide a broad overview around the scientific investigation of yogic effect on brain waves and cognitive functions. However, there are so many neurological mechanisms that contribute brain wave activities or neural oscillations which are not discussed properly. Few studies have provided the details of how randomization had been performed. Studies included that our reviews consist of various subtypes of yoga, and the description of the intensity of yoga has not been specified in many studies. Due to the nature of the intervention, blinding of subjects is challenging, while information regarding blinding of the appraiser has not been provided in most studies. The sample sizes were small in many studies and the generalizability of benefits eminent in participants demonstrates the motivation to participate and comply in studies of yoga and it may be questionable.
Acknowledgment
The researchers are thankful to the Ministry of Human Resource Development, University Grant Commission, Department of Physical Education and Sport Science, Visva-Bharati University, for providing their wholehearted cooperation in this work.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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