Effects of Long Term Yoga Practice, Breathing, and Meditation on Cognitive Function and Emotional Control: A Review of the Literature
In recent decades, in the Western world has spread an ancient discipline from India, Yoga.
The word Yoga comes from the Sanskrit root “yuj”, which can be translated as “union”, and indicates a very complex practice, closely linked to Indian culture, religious life, and traditions. Yoga consists mainly of three activities that are the control of posture (asana), breathing (pranayama) and meditation (dhyana). The posture control is determined by a number of positions that should be maintained for a minimum of 15 s to a maximum of variable duration depending on the position’s degree of difficulty, before moving on to the next one . The practice can become gradually more complex starting from simple positions that release the tensions of the spine, to those requiring prolonged strength and resistance. Pranayama is expressed first by observing and becoming aware of our natural breath and, later on, by the acquisition and exploration of different breath techniques. Finally, dhyana consists in experimenting a non-judgmental attitude towards the content of thought and, in an advanced phase, thoughts management and visualization. Its practices can be conducted into two different ways. On the one hand, “focused attention meditation” which concentrates on techniques that bring attention to a particular object of observation, be it mental, bodily or external; on the other, “open monitoring meditation” that resorts to techniques that seek to broaden the focus of all incoming information in each moment, whether they are sensations, emotions, and thoughts, without focusing on any of them. Nevertheless, most of the meditations use both approaches in a complementary way . A particular exercise that is similar in concept to meditation, but differs in its actualization, is the practice of reciting mantras, namely the rhythmic repetition of syllables and continuous, single words or short phrases for a certain period of time.
The goal that Yoga aims at through the inner experience is: experience the “mental” in an attempt to overcome it and reach “extraordinary” contemplation stages that differ from the states of consciousness experienced commonly. Such type of experience can also be described as a complex process that, through self-observation, aims at the self-regulation of the body and mind. This process is often associated with psychological and neurophysiological changes.
Numerous articles and scientific studies demonstrated that Yoga could be a valuable help in the improvement and maintenance of individual and, consequently, public health [3-6].
In the context of Western scientific research, the primary objective of Yoga is to optimize health, promote the reduction of stress and increase self-regulation, both as a preventative or treatment care .
The growing interest towards Yoga has also developed within the scientific community because interventions based on Yoga have been associated with measurable changes regarding physiological parameters, perceived emotional states and cognitive functioning .
Nowadays, it is common to observe that anxiety, depression, high-stress levels (as a biological reaction of the organism to stimuli that are identified as harmful, whether physical, chemical, biological or psychological) limit the normal course of daily activities and/or impact negatively on athletic performance.
The present review aimed to provide a wider overview on the neurophysiological effect of a long-term Yoga practice, and of pranayama and dhyana alone, on the cognitive function and emotional control. Having Yoga a theoretical basis and different cultural roots from Western ones, as part of this review particular emphasis on studies and works that bring objective data and measurable tests were given.
A comprehensive literature search for Yoga, breathing, meditation, cognitive function and emotional control was performed on the electronic databasesPubMed, Scopus, Web of Science, Embase and GoogleScholar for relevant articles published from January 2000 to September 2016. The key words used were Yoga, Asana, Breathing, Pranayama, Meditation, Cognitive function, Emotional control, Grey Matter, Brain effects, Amygdala, Hippocampus, Cerebral Cortex. The combination of keywords with #AND and #OR was performed. Only studies written in English were considered during databases searching. Journal articles, conference proceedings, and clinical reports were included for potentially eligible studies. Moreover, the reference list of all the articles was carefully checked.
Article titles and abstracts identified by the search were screened for potential relevance. The full text of all potentially relevant studies was reviewed to determine if it fulfilled the eligible criteria. Authors screened independently the results of the electronic searches to select potentially relevant citations according to the criteria defined above. The published works meeting the most relevant criteria were included. Studies without proper data presentation, with unclear or vague protocol description, and without an in-depth discussion were excluded from this review.
Authors analyzed the articles individually using an MS-Excel structured data extraction form purposely created for this review. Extracted data were compared and discussed by these two authors before being included in the final pile of reviewed papers. Information extracted from each article included: (a) type of practice, (b) methodological approach, (c) area of interest, (d) participants characteristics.
Authors analyzed the data extracted from the potentially relevant articles. After the analysis, only the information extracted from the most relevant studies (those organized with proper data presentation, clearly verified selection of protocols, and through demonstration of research methodologies) was discussed, to reduce the risk of bias.
All the articles were divided into three main areas: Yoga, Pranayama, and Dhyana. A description of these studies is presented in Tables 1, 2, and 3 in the Results section
Studies included in the revision process
The comprehensive literature search returned 210 articles (Figure 1). Of these, 80 met the inclusion criteria for ‘‘Yoga’’, 30 for ‘‘Pranayama’’, and 100 for “Dhyana”. Among Yoga articles, 50 were duplicated and were excluded, and 16 were excluded because out of topic, 6 for having a not clear protocol and/or not using imaging techniques. Among Pranayama articles, 15 were excluded because they were duplicated.
6 were excluded because out of topic and 7 for a poor protocol description and data presentation. Lastly, 50 articles for Dhyana were excluded because duplicated, 20 because out of topic and other 15 for having a not clear protocol and/or not using imaging techniques.
At the end of the revision process, reviewed articles for Yoga, Dhyana, and Pranayama were 8, 15, and 2 respectively.
Yoga articles are reported in Table 1. Four articles involved all the Yoga components (asana, pranayama and dhyana) [8-11], two articles combined pranayama and dhyana [12,13], and two combined asanas and dhyana (Kripalu Yoga)[14,15]. Six used MRI technique to evaluate cortical and subcortical area [8-11,14,15], one used fMRI , one utilized electroencephalography , and two included a questionnaire [9,11].
Pranayama studies are presented in Table 2. One study utilized a memory test  and the other used a near-infrared system analysis.
Dhyana articles are reported in Table 3. With the exception of two studies, which involved mantra meditation [18,19], the other thirteen articles involved both open monitoring and focused attention meditation. Nine studies utilized MRI technique[ 2,20-26 ], six used fMRI [2,18,19,27-30], two included the use of questionnaires [24,26], and one used diffusion tensor imaging technique to evaluate the changes in the uncinate fasciculus.
Figure 1. Flow chart of the process for selecting potential studies to be included in the present review.
The studies observed different kinds of modifications: the immediate neurofunctional correlations of the performed practice, the neurofunctional modifications after several training sessions and structural changes in expert practitioners.
The collection of data shows different variations of the structure of some encephalic formations and the modified perceptual- cognitive states reported by the subjects who participated in the research. In detail, studies found an increase in gray matter density and volume in cortical and limbic areas and a higher level of activation during the execution of the practice. The only structure showing a decrease of density and activation levels is the amygdala. The observed changes involve structures responsible for the management of stressors stimuli, emotional and perceptual control, cognitive functioning, memory processes, and self-observation. From a neural perspective, significant differences between the performance of Yoga or Dhyana do not emerge , excluding Pranayama considered singularly because there is not enough literature on this subject alone.
Among the areas of interest, the hippocampus shows structural modifications, i.e. an increase in gray matter concentration, even in the short term with the daily practice during the week [8-10]. The hippocampus is a key structure for the correct functioning of memory processes, both for learning and for the recovery of information and it is implicated in the regulation of emotional response: consequently, positive structural changes in this area may manifest through an enhanced functionality in the management of such processes .
To confirm this, a six-month study conducted on elderly subjects showed an increase of bilateral hippocampal volume. It is worth noting that hippocampal reduction in volume is one of the earliest indicators of Alzheimer’s disease, of severe depressive states and post-traumatic stress disorder .
The cerebral cortex also shows several areas of interest involved both during activation phase and that reveal structural changes and increased connectivity. These changes were noted n the following areas:
– Frontal Lobe: prefrontal cortex, middle and superior frontal gyrus , orbitofrontal cortex [10,11], precentral cortex , left frontal operculum, left inferior frontal gyrus, frontal medial cortex and right middle frontal cortex;
– Parietal Lobe: temporoparietal junction, junction of the temporal and parietal lobe , primary somatosensory cortex , precuneus , superior parietal network and medial parietal cortex ;
– Occipital Lobe: right lingual gyrus , right primary visual cortex , left lateral occipital cortex ;
– Temporal Lobe: middle and superior temporal gyrus [11,10];
– Limbic lobe: anterior cingulated cortex  and posterior cingulate cortex [9, 13];
Similarly, changes have been identified with regards to the activity and the morphology of the cerebellum [9,10].
Control subjects never showed higher volumes in the regions of interest, compared to subjects practicing Yoga [11,10].
A larger size of the prefrontal cortical regions may indicate a better cognitive control, inhibition of automatic responses, improved adaptive processes and, consequently, higher “decision- making skills”. The results of the Cognitive Failures Questionnaire confirmed the idea that a greater volume of gray matter in these regions is associated with fewer cognitive failures, memory, motor function in the execution of everyday tasks.
Higher volumes in the orbitofrontal cortical region suggest a better emotional control, which consequently leads to implement a correct answer to the demands of the external environment .
With regard to the parietal and temporal lobes, it has been suggested that the temporoparietal junction represents a fundamental structure for conscious experience, acting as a spatial mediator between consciousness and the body . It is also associated with the understanding of the desires, intentions, and moods of other people. The temporal gyri are instead part of a network of connections regarding the transition from harmless to painful sensations: Yoga practitioners carefully observe this kind of feeling increase flexibility but avoid painfully and possibly dangerous muscular stretching.
Pranayama and meditation together have been found to influence brain rhythms in frontal, parietal and occipital channels that, as a consequence, produce improvements in working memory capacity by reducing stress levels and promoting efficient use of energy in these regions.
Increased greater resting state functional connectivity found in the caudate, frontal, parietal and temporal regions, together with key components of basal ganglia and thalamocortical loops, are implicated in reinforcement learning and can result in improved behavioral flexibility, mental health and well-being[ 15]. Also, better small-worldness and integration in resting state networks shown in Yoga practitioners in these areas, result in a less age-related decline of fluid intelligence .
The insula lobe, or simply insula, is a region involved both in the recognition of bodily sensations and interoceptive states
MRI: Magnetic Resonance Imaging; fMRI: Functional Magnetic Resonance Imaging; VBM: Voxel-Based Morphometry; CF: Cognitive Failures questionnaire; FFMQ: Five Facet Mindful Questionnaire; PSS: Perceived Stress State questionnaire; PANAS: Positive And Negative Affect Schedule; BSI: Brief Symptom Inventory; ALE: Activation Likelihood Estimation; EEG: Electroencephalograph.
Table 1. Analysis of the studies involved in the review for Yoga.
and in attentional control [9,10]. A 2009 study indicates a fundamental role of the insula in the development of self-awareness .
As previously described, dhyana alone seems to induce effects hippocampus, amygdala and cerebral cortex level that are similar to Yoga. As far as the hippocampus is concerned, an 8-week meditation program aiming at stress reduction reported significant increases in gray matter in the left hippocampus . Also, larger gray matter volumes and higher density were found in practitioners with many years of experience [2, 7, 20]. These findings may indicate how dhyana, and Yoga practices, have the potential to increase the efficiency of memory processes, emotional control and, in general, the hippocampal activity, including neurogenesis.
Another observed structure, involved in the management of stressors stimuli, is the amygdala: a high activation of this area was detected in people suffering from anxiety and depression, post-traumatic stress disorder, social phobia and impulsive aggression . During the practice of dhyana has been observed, with the help of fMRI, a decreased bilateral activation of the amygdala  and, through images taken with MRI before and after intervention, a decrease in the density of grey matter in the right amygdala . As provided by the researchers, by administering the PSS Questionnaire and pairing it with the MRI data, to decreased stress levels corresponds a relative decrease in the density of gray matter in the right amygdala: this would be justified by the researches which suggest that the right amygdala acts as a mediator to the initial stimulus, through a quick and automatic detection of the stimulus itself, followed by a more discriminative response by the left amygdala. It must be specified, however, that if the isolated activation of the amygdala may indicate a situation of psychological stress, concomitant activation of the dorsolateral prefrontal cortex, the anterior cingulate cortex, and the hippocampus, seem to contribute to the modification of stressful memoriesand emotional memories. Further studies will have to clarify with more precision the effects of a simultaneous activation of the hippocampus and amygdala during the execution of yogic practices .
With regards to the cerebral cortex, studies found an increase in gray matter volume and/or density in the following areas:
– Frontal Lobe: prefrontal cortex, middle and superior frontal gyrus [2,28], left ventrolateral prefrontal cortex , orbitofrontal cortex , right ventromedial orbitofrontal cortex , precentral cortex [19,22], orbitofrontal dorsolateral cortex , right and middle superior frontal sulci ;
– Parietal lobe: fundus of central sulcus , temporoparietal junction, junction of the temporal and parietal lobe , precuneus
, right parietal cortex ;
– Occipital Lobe: middle occipital gyrus , inferior occipitotemporal visual cortex ;
– Temporal Lobe: left superior temporal gyrus , middle and superior temporal gyrus , inferior temporal gyrus, medial temporal lobe , fusiform gyrus , right inferior temporal cortex ;
– Limbic lobe: anterior cingulate cortex [2,18,28], medial cingulate cortex ;
The extracted data almost fully overlap with the findings obtained in the previous paragraph: this shows how the practice of Yoga (i.e. the combination of asana, pranayama, and dhyana) or dhyana alone, present similarities on a neural level regarding brain network organization, modifications and cognitive functioning .
In examining the studies that considered dhyana alone, the authors also found that the temporoparietal junction along
fMRI: Functional Magnetic Resonance Imaging; MRI: Magnetic Resonance Imaging; ALE: Activation Likelihood Estimation VBM: Voxel-Based Morphometry; EEG: Electroencephalograph; DTI: Diffusion Tensor Imaging; PWBS questionnaire: Psychological Well-Being Scales
Table 2. Analysis of the studies involved in the review for Dhyana.
with the dorsolateral prefrontal cortex and the superior parietal lobe, are associated with attentional orientation processes .
The temporal lobe instead, has been associated with mystical experiences characterized by a state of perception of union with the environment and compassion for others . These ‘states of being’ were reached through a long practice of meditation.
Only two studies considered and examined pranayama by itself. Researchers found that uninostril breathing (right nostril Yoga breathing) increases oxygenation and blood volume in the left prefrontal cortex as compared to breath awareness and left nostril Yoga breathing . Uninostril breathing practitioners also registered an increase in recall of digit span-forward, digit-span backward, associate learning and spatial memory scores .
Table 3. Analysis of the studies involved in the review for Pranayama. EEG: Electroencephalograph
Overall, the results of the present study suggest that Yoga and Meditation induce significant changes in the cognitive function and emotional control. These modifications, as noted by the study on the encephalic formations through the MRI techniques and questionnaires given to participants result in a better perceptive, cognitive and emotional state, which allows the achievement of an optimal health condition and a healthier approach to everyday life. The involvement and favorable changes in crucial areas devoted to stress management and emotional and cognitive processes, show an increase in the volume or density of gray matter in the hippocampus and the cerebral cortex area, and a reduction in the density of the amygdala. These are key structures for the person’s well-being.
The significant decrease in stress levels observed in individuals examined during the experiments is particularly important when taking into account the social context of the Western world, which tends towards increasingly frenetic pace and a prevailing individualism.
New studies in this matter will also confirm the counteraction of Yoga towards near senescence, i.e. the aging of brain cells, and then propose the integration of these practices in a program for the maintenance or improvement of health. This objective is feasible through a process that integrates these activities during the daily routine.
Before we can proceed with the integration of these exercises within a clinical or educational program, the authors state the need for further investigation and studies about them. It has not been investigated, for example, how any practice considered individually (asana, pranayama, and dhyana) affects brain activity specific to each area examined. During the practice of Yoga, in fact, these three activities are present simultaneously and influence each other. Moreover, some authors suggested maintaining two of these three activities in fixed parameter and change in a more accentuated the third, so as to have a clearer representation of what the area interest of the central nervous system that is stimulated by each practice.
As indicated by, knowledge of behavioral neurobiological mechanisms is also indispensable for a more targeted use of this discipline.
It appears nevertheless clear from the foregoing analysis that practices based on Yoga, whether performed individually or in combination, make changes lasting benefits, which will vary based on the amount of commitment and perseverance being made in the implementation of Yoga itself.
A particular thanks go to Dr. Chiara Marozzo for critically revising the manuscript.
Authors have no conflicts of interest.
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