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EEG technology has been used for meditation research
For the purpose of this article, research on meditation concerns research into the psychological and physiological effects of meditation using the scientific method. In recent years, these studies have increasingly involved the use of modern scientific techniques and instruments, such as fMRI and EEG which are able to directly observe brain physiology and neural activity in living subjects, either during the act of meditation itself, or before and after a meditation effort, thus allowing linkages to be established between meditative practice and changes in brain structure or function.
Since the 1950s hundreds of studies on meditation have been conducted. Yet, many of the early studies were flawed and thus yielded unreliable results.[1][2] Contemporary studies have attempted to address many of these flaws with the hope of guiding current research into a more fruitful path.[3] In 2013, researchers at Johns Hopkins, publishing in the Journal of the American Medical Association, identified 47 studies that qualify as well-designed and therefore reliable. Based on these studies, they concluded that there is moderate evidence that meditation reduces anxiety, depression, and pain, but there is no evidence that meditation is more effective than active treatment.[4] 2017 commentary was similarly mixed.[5][6]
The process of meditation, as well as its effects, is a growing subfield of neurological research.[7][8] Modern scientific techniques and instruments, such as fMRI and EEG, have been used to study how regular meditation affects individuals by measuring brain and bodily changes.[7][9][10]
Meditation is a broad term which encompasses a number of practices.[vague][citation needed]
Weaknesses in historic meditation and mindfulness research
A comparison of the effect of various meditation techniques on systolic blood pressure.[1]
In June, 2007 the United States National Center for Complementary and Integrative Health (NCCIH) published an independent, peer-reviewed, meta-analysis of the state of meditation research, conducted by researchers at the University of Alberta Evidence-based Practice Center. The report reviewed 813 studies involving five broad categories of meditation: mantra meditation, mindfulness meditation, yoga, T'ai chi, and Qigong, and included all studies on adults through September 2005, with a particular focus on research pertaining to hypertension, cardiovascular disease, and substance abuse. The report concluded, "Scientific research on meditation practices does not appear to have a common theoretical perspective and is characterized by poor methodological quality. Firm conclusions on the effects of meditation practices in healthcare cannot be drawn based on the available evidence. Future research on meditation practices must be more rigorous in the design and execution of studies and in the analysis and reporting of results." (p. 6) It noted that there is no theoretical explanation of health effects from meditation common to all meditation techniques.[1]
A version of this report subsequently published in the Journal of Alternative and Complementary Medicine stated that "Most clinical trials on meditation practices are generally characterized by poor methodological quality with significant threats to validity in every major quality domain assessed". This was the conclusion despite a statistically significant increase in quality of all reviewed meditation research, in general, over time between 1956 and 2005. Of the 400 clinical studies, 10% were found to be good quality. A call was made for rigorous study of meditation.[3] These authors also noted that this finding is not unique to the area of meditation research and that the quality of reporting is a frequent problem in other areas of complementary and alternative medicine (CAM) research and related therapy research domains.
Of more than 3,000 scientific studies that were found in a comprehensive search of 17 relevant databases, only about 4% had randomised controlled trials (RCTs), which are designed to exclude the placebo effect.[1]
A 2013 statement from the American Heart Association evaluated the evidence for the effectiveness of TM as a treatment for hypertension as "unknown/unclear/uncertain or not well-established", and stated: "Because of many negative studies or mixed results and a paucity of available trials... other meditation techniques are not recommended in clinical practice to lower BP at this time."[11]
2017 commentary was similarly mixed,[5][6] with concerns including the particular characteristics of individuals who tend to participate in mindfulness and meditation research.[12]
Mindfulness
One meta-analysis supported the use of Mindfulness-Based Stress Reduction (MBSR) to alleviate symptoms of a variety of mental and physical disorders.[13] A previous study commissioned by the US Agency for Healthcare Research and Quality found that meditation interventions reduce multiple negative dimensions of psychological stress.[4] Other systematic reviews and meta-analysis show that mindfulness meditation has several mental health benefits such as bringing about reductions in depression symptoms,[14][15][16] and mindfulness interventions also appear to be a promising intervention for managing depression in youth.[17][18] Mindfulness meditation is useful for managing stress,[15][19][20] anxiety,[14][15][20] and also appears to be effective in treating substance use disorders.[21][22][23] A recent meta analysis by Hilton et al. (2016) including 30 randomized controlled trials found high quality evidence for improvement in depressive symptoms.[24] Other review studies have shown that mindfulness meditation can enhance the psychological functioning of breast cancer survivors,[15] effective for eating disorders,[25][26] and may also be effective in treating psychosis.[27][28][29]Studies have also shown that rumination and worry contribute to mental illnesses such as depression and anxiety,[30] and mindfulness-based interventions are effective in the reduction of worry.[30][31]
Some studies suggest that mindfulness meditation contributes to a more coherent and healthy sense of self and identity, when considering aspects such as sense of responsibility, authenticity, compassion, self-acceptance and character.[32][33]
Mindfulness scales
In the relatively new field of western psychological mindfulness, researchers attempt to define and measure the results of mindfulness primarily through controlled, randomised studies of mindfulness intervention on various dependent variables. The participants in mindfulness interventions measure many of the outcomes of such interventions subjectively. For this reason, several mindfulness inventories or scales (a set of questions posed to a subject whose answers output the subject's aggregate answers in the form of a rating or category) have arisen. Twelve such methods are mentioned by the Mindfulness Research Guide[34]Brain mechanisms
In 2011, National Center for Complementary and Integrative Health (NCCIH) released findings from a study in which magnetic resonance images were taken of the brains of 16 participants 2 weeks before and after the participants joined the mindfulness meditation (MM) program by researchers from Massachusetts General Hospital, Bender Institute of Neuroimaging in Germany, and the University of Massachusetts Medical School. Researchers concluded that..these findings may represent an underlying brain mechanism associated with mindfulness-based improvements in mental health.[35]The analgesic effect of MM involves multiple brain mechanisms including the activation of the anterior cingulate cortex and the ventromedial prefrontal cortex.[36] In addition, brief periods of MM training increases the amount of grey matter in the hippocampus and parietal lobe.[37] Other neural changes resulting from MM may increase the efficiency of attentional control.[38]
Participation in MBSR programmes has been found to correlate with decreases in right basolateral amygdala gray matter density,[39] and increases in gray matter concentration within the left hippocampus.[40]
Changes in the brain
Mindfulness meditation also appears to bring about favorable structural changes in the brain, though more research needs to be done because most of these studies are small and have weak methodology.[41][7][9][10] One recent study found a significant cortical thickness increase in individuals who underwent a brief -8 weeks- MBSR training program and that this increase was coupled with a significant reduction of several psychological indices related to worry, state anxiety, depression.[42] Another study describes how mindfulness based interventions target neurocognitive mechanisms of addiction at the attention-appraisal-emotion interface.[22] A meta-analysis by Fox et al. (2014) using results from 21 brain imaging studies found consistent differences in the region of the prefrontal cortex and other brain regions associated with body awareness. In terms of effect size the mean effect was rated as moderate. (Cohen's d = 0.46) However the results should be interpreted with caution because funnel plots indicate that publication bias is an issue in meditation research.[41] A follow up by Fox et al. (2016) using 78 functional neuro-imaging studies suggests that different meditation styles are reliably associated with different brain activity. Activations in some brain regions are usually accompanied by deactivation in others. This finding suggests that meditation research must put emphasis on comparing practices from the same style of meditation, for example results from studies investigating focused attention methods cannot be compared to results from open monitoring approaches.[43]Attention and mindfulness
Attention networks and mindfulness meditation
Psychological and Buddhist conceptualisations of mindfulness both highlight awareness and attention training as key components, in which levels of mindfulness can be cultivated with practise of mindfulness meditation.[44] Focused attention meditation and open monitoring meditation are distinct types of mindfulness meditation, and the former relates to directing and maintaining attention on a chosen object (e.g. the breath).[45] Open monitoring meditation does not involve focus on a specific object, and instead awareness is grounded in the perceptual features of one’s environment.Focused attention meditation is typically practiced first to increase the ability to enhance attentional stability, and awareness of mental states with the goal being to transition to open monitoring meditation practise that emphasizes the ability to monitor moment-by-moment changes in experience, without a focus of attention to maintain. Mindfulness meditation may lead to greater cognitive flexibility [46]
Evidence for improvements in three areas of attention
Sustained attention Tasks of sustained attention relate to vigilance and the preparedness that aids completing a particular task goal. Psychological research into the relationship between mindfulness meditation and the sustained attention network have revealed the following:- Mindfulness meditators have demonstrated superior performance when the stimulus to be detected in a task was unexpected, relative to when it was expected. This suggests that attention resources were more readily available in order to perform well in the task. This was despite not receiving a visual cue to aid performance. (Valentine & Sweet, 1999).
- In a Continuous performance task [47] an association was found between higher dispositional mindfulness and more stable maintenance of sustained attention.
- In an EEG study,[48] the Attentional blink effect was reduced, and P3b ERP amplitude decreased in a group of participants that completed a mindfulness retreat.[49] The incidence of reduced attentional blink effect relates to an increase in detectability of a second target. This may have been due to a greater ability to allocate attentional resources for detecting the second target, reflected in a reduced P3b amplitude.
- A greater degree of attentional resources may also be reflected in faster response times in task performance, as was found for participants with higher levels of mindfulness experience.[50]
- Selective attention as linked with the orientation network, is involved in selecting the relevant stimuli to attend to.
- Performance in the ability to limit attention to potentially sensory inputs (i.e. selective attention) was found to be higher following the completion of an 8-week MBSR course, compared to a one-month retreat and control group (with no mindfulness training).[50] The ANT task is a general applicable task designed to test the three attention networks, in which participants are required to determine the direction of a central arrow on a computer screen.[51] Efficiency in orienting that represent the capacity to selectively attend to stimuli was calculated by examining changes in the reaction time that accompanied cues indicating where the target would occur relative to the aid of no cues.
- Meditation experience was found to correlate negatively with reaction times on an Eriksen flanker task measuring responses to global and local figures. Similar findings have been observed for correlations between mindfulness experience in an orienting score of response times taken from Attention Network Task performance.[52]
- More than one study have reported findings of a reduced Stroop effect following mindfulness meditation training.[46][53][54] The Stroop effect indexes interference created by having words printed in colour that differ to the read semantic meaning e.g. green printed in red. However findings for this task are not consistently found.[55][10] For instance the MBSR may differ to how mindful one becomes relative to a person who is already high in trait mindfulness.[38]
- Using the Attention Network Task (a version of Eriksen flanker task [51]) it was found that error scores that indicate executive control performance were reduced in experienced meditators [50] and following a brief 5 session mindfulness training program.[53]
- A neuroimaging study supports behavioural research findings that higher levels of mindfulness are associated with greater proficiency to inhibit distracting information. As greater activation of the rostral anterior cingulate cortex (ACC) was shown for mindfulness meditators than matched controls.
- Following a Stroop test, reduced amplitude of the P3 ERP component was found for a meditation group relative to control participants. This was taken to signify that mindfulness meditation improves executive control functions of attention. An increased amplitude in the N2 ERP component was also observed in the mindfulness meditation group, thought to reflect more efficient perceptual discrimination in earlier stages of perceptual processing.[56]
Emotion regulation and mindfulness
Reductions in rumination have been found following Mindfulness meditation practise.[57][58]Evidence of mindfulness and emotion regulation outcomes
Emotional reactivity can be measured and reflected in brain regions related to the production of emotions.[59] It can also be reflected in tests of attentional performance, indexed in poorer performance in attention related tasks. The regulation of emotional reactivity as initiated by attentional control capacities can be taxing to performance, as attentional resources are limited [60]- Patients with social anxiety disorder (SAD) exhibited reduced amygdala activation in response to negative self-beliefs following an MBSR intervention program that involves mindfulness meditation practise [61]
- The LPP ERP component indexes arousal and is larger in amplitude for emotionally salient stimuli relative to neutral.[62][63][64] Individuals higher in trait mindfulness showed lower LPP responses to high arousal unpleasant images. These findings suggest that individuals with higher trait mindfulness were better able to regulate emotional reactivity to emotionally evocative stimuli.[65]
- Participants that completed a 7-week mindfulness training program demonstrated a reduction in a measure of emotional interference (measured as slower responses times following the presentation of emotional relative to neutral pictures). This suggests a reduction in emotional interference.[66]
- Following a MBSR intervention, decreases in social anxiety symptom severity were found, as well as increases in bilateral parietal cortex neural correlates. This is thought to reflect the increased employment of inhibitory attentional control capacities to regulate emotions [67][68]
- Mindfulness has been found to reduce subsequent distress.[69]
Controversies in mindful emotion regulation
It is debated as to whether top-down executive control regions such as the Dorsolateral prefrontal cortex (DLPFC),[70] are required [68] or not [61] to inhibit reactivity of the amygdala activation related to the production of evoked emotional responses. Arguably an initial increase in activation of executive control regions developed during mindfulness training may lessen with increasing mindfulness expertise [71]Prevention of mental illness
An 8 week mindfulness course given to students was found to reduce the number subsequently needing treatment for mental illness by 60%, although the study was not of large size and commented that the effect could be due to 'non-specific effects', as the control group had received no attention at all, rather than an alternative intervention.[69]Future directions
A large part of mindfulness research is dependent on technology. As new technology continues to be developed, new imaging techniques will become useful in this field. It would be interesting to use real-time fMRI to help give immediate feedback and guide participants through the programs. It could also be used to more easily train and evaluate mental states during meditation itself.[72] The new technology in the upcoming years offers many exciting potentials for the continued research.Research on other types of meditation
Insight (Vipassana) meditation
Vipassana meditation is a component of Buddhist philosophy. Phra Taweepong Inwongsakul and Sampath Kumar from the University of Mysore have been studying the effects of this meditation on 120 students by measuring the associated increase of cortical thickness in the brain. The results of this study are inconclusive.[73][74]Sahaja yoga and mental silence
Sahaja yoga meditation is regarded as a mental silence meditation, and has been shown to correlate with particular brain[75][76] and brain wave[77][78][79] characteristics. One study has led to suggestions that Sahaja meditation involves 'switching off' irrelevant brain networks for the maintenance of focused internalized attention and inhibition of inappropriate information.[80] Sahaja meditators appear to benefit from lower depression[81] and scored above control group for emotional well-being and mental health measures on SF-36 ratings.[82][83][84]A study comparing practitioners of Sahaja Yoga meditation with a group of non meditators doing a simple relaxation exercise, measured a drop in skin temperature in the meditators compared to a rise in skin temperature in the non meditators as they relaxed. The researchers noted that all other meditation studies that have observed skin temperature have recorded increases and none have recorded a decrease in skin temperature. This suggests that Sahaja Yoga meditation, being a mental silence approach, may differ both experientially and physiologically from simple relaxation.[79]
Kundalini Yoga
Kundalini Yoga has proved to increase the prevention of cognitive decline and evaluate the response of biomarkers to treatment, thereby shedding light on the underlying mechanisms of the link between Kundalini Yoga and cognitive impairment. For the study, 81 participants aged 55 and older who had subjective memory complaints and met criteria for mild cognitive impairment, indicated by a total score of 0.5 on the Clinical Dementia Rating Scale. The results showed that at 12 weeks, both the yoga group showed significant improvements in recall memory and visual memory and showed significant sustained improvement in memory up to the 24-week follow-up, the yoga group showed significant improvement in verbal fluency and sustained significant improvements in executive functioning at week 24. In addition, the yoga cohort showed significant improvement in depressive symptoms, apathy, and resilience from emotional stress. This research was provided by Helen Lavretsky, M.D. and colleagues.[85] In another study, Kundalini Yoga did not show significant effectiveness in treating obsessive-compulsive disorders compared with Relaxation/Meditation.[86]Transcendental Meditation
The first Transcendental Meditation (TM) research studies were conducted at UCLA and Harvard University and published in Science and the American Journal of Physiology in 1970 and 1971.[87] However, much research has been of poor quality,[1][86][88] including a high risk for bias due to the connection of researchers to the TM organization and the selection of subjects with a favorable opinion of TM.[89][90][91] Independent systematic reviews have not found health benefits for TM exceeding those of relaxation and health education.[1][86][90] A 2013 statement from the American Heart Association described the evidence supporting TM as a treatment for hypertension as Level IIB, meaning that TM "may be considered in clinical practice" but that its effectiveness is "unknown/unclear/uncertain or not well-established".[this quote needs a citation] In another study, TM proved comparable with other kinds of relaxation therapies in reducing anxiety.[86]Research on unspecified or multiple types of meditation
Brain activity
The medial prefrontal and posterior cingulate cortices have been found to be relatively deactivated during meditation (experienced meditators using concentration, lovingkindness and choiceless awareness meditation). In addition experienced meditators were found to have stronger coupling between the posterior cingulate, dorsal anterior cingulate, and dorsolateral prefrontal cortices both when meditating and when not meditating.[92]Mental health
A meta analysis found meditation gave some benefits, but no evidence that it was better than other treatments, for mental illness.[4]Physical changes in the brain
Meditation has been shown to change grey matter concentrations and the precuneus.[93][40][94][41][39]An eight-week MBSR course induced changes in gray matter concentrations.[40] Exploratory whole brain analyses identified significant increases in gray matter concentration in the PCC, TPJ, and the cerebellum. These results suggest that participation in MBSR is associated with changes in gray matter concentration in brain regions involved in learning and memory processes, emotion regulation, self-referential processing, and perspective taking.
Perception
Studies have shown that meditation has both short-term and long-term effects on various perceptual faculties. In 1984 a study showed that meditators have a significantly lower detection threshold for light stimuli of short duration.[95] In 2000 a study of the perception of visual illusions by zen masters, novice meditators, and non-meditators showed statistically significant effects found for the Poggendorff Illusion but not for the Müller-Lyer Illusion. The zen masters experienced a statistically significant reduction in initial illusion (measured as error in millimeters) and a lower decrement in illusion for subsequent trials.[96] Tloczynski has described the theory of mechanism behind the changes in perception that accompany mindfulness meditation thus: "A person who meditates consequently perceives objects more as directly experienced stimuli and less as concepts… With the removal or minimization of cognitive stimuli and generally increasing awareness, meditation can therefore influence both the quality (accuracy) and quantity (detection) of perception."[96] Brown also points to this as a possible explanation of the phenomenon: "[the higher rate of detection of single light flashes] involves quieting some of the higher mental processes which normally obstruct the perception of subtle events."[this quote needs a citation] In other words, the practice may temporarily or permanently alter some of the top-down processing involved in filtering subtle events usually deemed noise by the perceptual filters.[citation needed]Relaxation response
Herbert Benson, founder of the Mind-Body Medical Institute, which is affiliated with Harvard University and several Boston hospitals, reports that meditation induces a host of biochemical and physical changes in the body collectively referred to as the "relaxation response".[97] The relaxation response includes changes in metabolism, heart rate, respiration, blood pressure and brain chemistry. Benson and his team have also done clinical studies at Buddhist monasteries in the Himalayan Mountains.[98] Benson wrote The Relaxation Response to document the benefits of meditation, which in 1975 were not yet widely known.[99]Calming effects
According to an article in Psychological Bulletin, EEG activity slows as a result of meditation.[100] The National Institutes of Health (NIH) has written, "It is thought that some types of meditation might work by reducing activity in the sympathetic nervous system and increasing activity in the parasympathetic nervous system,"[this quote needs a citation] or equivalently, that meditation produces a reduction in arousal and increase in relaxation.[citation needed]Slowing aging
Aging is a process accompanied by a decrease in brain weight and volume. This phenomenon can be explained by structural changes in the brain, namely, a loss of grey matter. Some studies over the last decade have implicated meditation as a protective factor against normal age-related brain atrophy.[101] The first direct evidence for this link emerged from a study investigating changes in the cortical thickness of meditators. Interestingly, the researchers found that regular meditation practice was able to reduce age-related thinning of the frontal cortex, albeit, these findings were restricted to particular regions of the brain.[102] A similar study looked to further expand on this finding by including a behavioural component. Consistent with the previous study, meditators did not show the expected negative correlation between grey matter volume and age. In addition, the results for meditators on the behavioural test, measuring attentional performance, were comparable across all age groups.[103] This implies that meditation can potentially protect against age-related grey matter loss and age-related cognitive decline. Since then, more research has supported the notion that meditation serves as a neuroprotective factor that slows age-related brain atrophy.[101][104] Still, all studies have been cross sectional in design. Furthermore, these results merely describe associations and do not make causal inferences.[105] Further work using longitudinal and experimental designs may help solidify the causal link between meditation and grey matter loss. Since few studies have investigated this direct link, however insightful they may be, there is not sufficient evidence for a conclusive answer.Research has also been conducted on the malleable determinants of cellular aging in an effort to understand human longevity. Researchers have stated, "We have reviewed data linking stress arousal and oxidative stress to telomere shortness. Meditative practices appear to improve the endocrine balance toward positive arousal (high DHEA, lower cortisol) and decrease oxidative stress. Thus, meditation practices may promote mitotic cell longevity both through decreasing stress hormones and oxidative stress and increasing hormones that may protect the telomere."[106][107]
Happiness
Studies have shown meditators to have higher happiness than control groups, although this may be due to non-specific factors such as meditators having better general self-care.[108][109][82][110]Yongey Mingyur Rinpoche has said that neuro scientists have found that with meditation, an individual's happiness baseline can change.[111]
Positive relationships have been found between the volume of gray matter in the right precuneus area of the brain and both meditation and the subject's subjective happiness score.[112][93][40][94][41][39]
Potential adverse effects and limits of meditation
The following is an official statement from the US government-run National Center for Complementary and Integrative Health:"Meditation is considered to be safe for healthy people. There have been rare reports that meditation could cause or worsen symptoms in people who have certain psychiatric problems, but this question has not been fully researched. People with physical limitations may not be able to participate in certain meditative practices involving physical movement. Individuals with existing mental or physical health conditions should speak with their health care providers prior to starting a meditative practice and make their meditation instructor aware of their condition."[113]Adverse effects have been reported,[114][115] and may, in some cases, be the result of "improper use of meditation".[116] The NIH advises prospective meditators to "ask about the training and experience of the meditation instructor… [they] are considering."[113]
As with any practice, meditation may also be used to avoid facing ongoing problems or emerging crises in the meditator's life. In such situations, it may instead be helpful to apply mindful attitudes acquired in meditation while actively engaging with current problems.[117][118] According to the NIH, meditation should not be used as a replacement for conventional health care or as a reason to postpone seeing a doctor.[113]
