What are the effects of yoga and meditation on the brain? (Asked by @leximills)
Yoga and meditation have effects on physiology, brain chemistry, and cognitive processes; these vary depending on the exact type of practise being performed and how long a person has practised it for. Studies of brain activity confirm that meditation can achieve a state of calm, thoughtless awareness, by suppressing brain regions involved in external attention and irrelevant information, and activating brain regions involved in internalised attention and positive emotions. Meditation is thought to activate the parasympathetic-limbic pathways, reducing heart rate, lowering blood pressure and slowing breathing. Meditation practises can fundamentally change the shape, structure and function of the brain – reinforcing neural networks, developing particular brain regions and influencing the production of key neurotransmitters and hormones in the brain related to attention, self-awareness and emotional control. Yoga has far-reaching effects on the body, reducing inflammation, boosting mood and making long-term practitioners feel more awake. It may even speed up learning in childhood and slow the natural cognitive declines that come with ageing. However, our understanding of the effects of meditative practises on the brain and body is still in its infancy – much more work remains (especially large-scale, carefully controlled trials).
Before we delve any further, let’s get some definitions out of the way. Meditation refers to a collection of techniques to achieve physical and mental relaxation, in the hope of achieving a higher mode of consciousness. It can involve both concentration and relaxation techniques, as well as breathing and visualisation exercises. Yoga, on the other hand, refers to a group of physical, mental and spiritual practises that aim to control the body and mind and again, reach higher levels of consciousness. Meditation forms a part of yoga, although yoga also incorporates physical exercises designed to build core strength and improve balance.
Although Western psychology describes three states of consciousness – asleep, dreaming and awake – Eastern philosophy describes an additional higher state of consciousness – thoughtless awareness. It is this fourth state of being, free from ‘mental clutter’, that meditation and yoga seek to elicit. And it seems, based on the EEG and brain-imaging data available, that meditation can succeed in achieving a brain state that is entirely separate from those experienced during every day life. Studies have also suggested that meditation can enhance psychological balance and emotional stability.
Experienced meditators show physiological changes during meditation including decreased sympathetic nervous activity (involved in the fight or flight response) and increased activity in the parasympathetic nervous system (involved in relaxation and rest). This ‘wakeful hypometabolic state’, quantitatively different from rest or sleep, may represent the fourth state aspired to by practitioners of meditation and yoga.
Mindfulness meditation, a type of meditation that focuses on one’s internal state in the present moment – often achieved by observing but not controlling breathing – has been particularly linked with changes in brain structure and improved cognitive processing. It has also been linked to delayed cognitive decline with ageing, and in speeding the learning process in children.
In a study published earlier this year, Joshua Rooks and colleagues compared the effects of mindfulness training and relaxation training on the attention span and emotional well-being of 100 college football players, finding that mindfulness training alone correlated with increased attention span in a response task, while both types of training reduced anxiety in the run up to a new football season.
At a physiological level, after a three-month yoga and meditation retreat, participants showed decreased anxiety and depression lined to increased levels of brain-derived neurotropic factor (BDNF), reduced levels of pro-inflammatory factors, and an extra boost of cortisol upon waking. Another study found that long-term meditators had a reduced psychological, physiological and electrophysiological reaction to stressful stimuli, suggesting that those who regularly practise meditation may have greater resilience to stressful events.
Studies suggest that children can particularly benefit from mindfulness training and meditation. For instance, one study followed over 240 children who were practising mindfulness meditation as part of their curriculum, and found that it was associated with earlier development of self-regulation.
Meditation can also be a powerful form of rehabilitation. For example, meta-analysis of prison yoga and meditation programs found that prisoners experienced increased wellbeing and showed better behaviour, particularly in long-term programs.
Finally, meditation and yoga may help ameliorate the damage caused by long-term stress and slow declines in cognitive function with ageing. Mindfulness training can slow the memory declines and reduce susceptibility to distraction that is often exhibited by military personnel under the persistent, intensive demands of training or combat. Mindfulness training was particularly effective in protecting military cohorts against this cognitive degradation, the study concluded.
However, how many of these benefits are truly due to the thoughts and focus of the brain during meditation? Just simple muscle relation is linked to activation in paralimbic and limbic regions involved in the sympathetic nervous system. Meditation practices that focus on breathing and introspection tend to activate similar regions, but most meditation techniques also activate the limbic and parietal networks involved in inward attention.
What’s going on in the brain?
A special issue of the Journal of Cognitive Enhancement this June included 16 articles on how different forms of meditation may enhance brain function. The studies found that long-term meditation can influence the strength of networks in the brain, alter the size of particular brain regions, and alter the amount of grey matter in the brain.
Electroencephalography (EEG) studies, which measure electrical signals in the brain by attaching electrodes to the scalp, can also reveal how meditation impacts neural activity. Such studies have commonly found that it increases activity in theta and alpha bandwidths – between 4 and 15 Hz – which are thought to reflect relaxation and a greater attention to internal events.
Sahaja Yoga, a meditation technique that aims to eliminate thought processes, has been shown to fundamentally alter the EEG signals of long-term practitioners. After 6 months of practise, EEG patterns unique to the meditator’s state of thoughtless awareness were detected. Practitioners showed increased theta and alpha wave activity, particularly in the left frontal lobe (a region thought to be involved in positive emotions), an effect that was most pronounced in meditators who also reported greater happiness during meditation. Other studies have suggested that alpha and theta activity becomes greater with practise.
So meditation practises that promote thoughtless awareness and internal focus seem to increase low frequency brain activity associated with relaxation and emotional control. But meditation practises with a different slant may have different effects. For instance, one small study compared eight experienced Tibetan Buddhist practitioners to novices and found that experienced meditators showed higher levels of gamma activity while focussing on feelings of compassion. In fact, this highly synchronised gamma activity across their frontal and parietal lobes – thought to be related to emotional processing – were the highest ever-recorded in healthy brains. This hints that concentrative practices may have fundamentally different effects on the brain to those achieved through thoughtless awareness.
Neuroimaging techniques, such as Magnetic Resonance Imaging (MRI) and it’s sibling fMRI, which use radio waves and strong magnetic fields to generate images of soft tissue and blood flow, have revealed more about the brain regions most affected by meditation. In general, meditation is associated with increased blood flow to the brain, particularly regions involved in attention and emotional regulation.
For example, one MRI comparison of regular mediators and non-meditators showed differences in connectivity between the medial prefrontal cortex, posterior cingulate cortex, the lateral temporal cortex and the hippocampus – brain regions in the Default Mode Network (DMN), which deals with self-referential thoughts.
A study comparing new meditators before and after an eight-week programme of mindfulness-based stress reduction found that they had denser grey matter around the left hippocampus, posterior cingulate cortex, temporoparietal junction (where the temporal and parietal lobes meet) and the cerebellum, than a control group who had never meditated. Larger grey matter reserves in these areas may improve learning and memory, attention, self-control, emotional regulation, compassion and self-awareness.
However, there is evidence that meditation can take time to take effect on the brain. For example, in a study of participants of a 6-day intensive Vipassana mindfulness retreat, there was no significant difference in cognitive flexibility between attendees and a control group who did not attend the retreat. In contrast, studies of long-term meditators have shown they have faster reaction times, better attention control and emotional recognition, and lower levels of anxiety, neuroticism and depression. Even just a few weeks or months of training can enhance performance on attention tasks. Alpha-theta brain patterns elicited during concentration meditation techniques employed by several yoga traditions have also been observed in practitioners at rest, suggesting long-term effects on brain activity.
In a study of 20 Buddhist meditators (who’d been practising for 9 years on average), researchers found increased cortical thickness in the prefrontal cortex and right anterior insular cortex – regions linked to attention, sensory processing and self-awareness. This effect was particularly pronounced in elderly meditators, suggesting that meditation may help to slow natural cortical thinning with age.
Another study using fMRI to study the brains of forty-six Sahaja practitioners, with an average of 14 years experience, revealed greater grey matter, particularly in the right hemisphere around the insular cortex, the orbitofrontal cortex, interior temporal cortex and parietal cortex, compared to non-meditators. These regions are associated with attention, self-control, compassion and self-awareness. Further, studies of Sahaja meditators have shown greater hemispheric balance even at rest – separating them from the majority of the population that have a left-hemisphere dominance.
Yoga practitioners show slower declines in grey matter with age, and years of yoga experience correlated positively with grey matter volume in the left hemisphere. Although it’s significance remains illusive, grey matter increases during childhood and declines with age, and is correlated with behaviour and IQ – we’re pretty sure it’s important, and meditation seems to help maintain it as we age. Regular practise makes a difference, too – the number of hours of yoga per week correlated with the volume of grey matter in particular brain regions such as the hippocampus (associated with long-term memory), visual cortex and cingulate cortex (involved in emotion forming and processing).
One study of Yoga Nidra meditation, which uses breathing exercises to reach a detached state with enhanced sensory awareness, detected a 65% increase in dopamine release in limbic brain regions (hippocampus, hypothalamus, amygdala) during the practise. Dopamine is a key neurotransmitter involved in happiness, wellbeing and motivation. Other studies have detected increases in blood levels of melatonin, a hormone involved in sleep and waking and serotonin, the so-called ‘happiness hormone’*, in long-term meditators. These chemical signals are likely to contribute to the feelings of wellbeing and calm experienced during meditation.
Both serotonin and dopamine have been strongly implicated in mood and mental illness, and meditation may therefore have an important role to play in reducing stress, easing the symptoms of depression and treating mood disorders. Melatonin has also been shown to stimulate the immune system and the body’s natural antioxidant defence system, potentially playing a role in ageing.
* It’s a bit more complicated than that
Healthy Immune System
Some research even suggests meditation may be beneficial to the immune system. As well as reducing stress and anxiety, known to negatively impact immune function, meditation has been shown to increase gene expression of key factors involved in innate immunity and inflammation.
So it’s all figured out?
One caveat with most of the studies I’ve cited is that the majority compared meditators with non-meditators, thereby ignoring the possibility that there are underlying differences between these two groups of people to start with. Perhaps people who are inclined to take up meditation and to stick with it (and to get involved in a study about it) also tend to have increased brain activation in limbic regions and higher levels of serotonin and dopamine? While that might be unlikely, studies which compel their subjects to take up meditation and compare them to a control group who don’t take it up, will go a long way to supporting the model presented by less controlled studies to date. Those studies that have employed this type of design are starting to back-up the comparative studies. For example, a study published earlier this year found that just six weeks of mindfulness-based health and wellness training resulted in a significant increase in the size of the left posterior insular cortex, a region though to be involved in perception, empathy, self-awareness, and attention.
Just as in many areas of science, our understanding of the impact of yoga and meditation on the brain and body is based on many small studies with not-exactly-representative-samples. We simply don’t have enough information yet to fully appraise what’s going on, and yoga and meditation may well have vastly different effects on people around the world than they do on 20-something American college undergrads.
But what is clear is that these practices do have a measurable long-term effect that is complex and depends a lot on the specifics of the programme you’re looking at. Meditation and yoga seem to boost self-awareness, concentration and attention by changing patterns of neuronal activity in the brain, altering levels of chemical messengers such as neurotranmitters and hormones and in the longer-term, strengthening neural connections between key brain regions, and growing and thickening grey matter. Meditative practises that focus on concentration may help boost attention by increasing connectivity in those regions of the brain – the more you use that part of your brain, the stronger the neural connections become. Many of the other benefits are physiological – by slowing your breathing and taking a break from whatever stresses may be happening in your life, it’s hard to see how yoga and meditation wouldn’t calm you down and boost your emotional well-being, with well-known knock on effects such as boosting the immune system. Finally, yoga can have significant physical benefits as well as mental ones – improved flexibility and core strength can help stave off many of the ailments of old age.
There doesn’t seem to be a downside to taking half an hour out of your day to do a little yoga or meditate – it’s certainly one of my favourite ways to de-stress, so it’s nice to know it’s backed up by some actual science!
Want to Know More?
Increased grey matter associated with long-term Sahaja yoga meditation: A voxel-based morphometry study. . Journal of PloS one, 11(3), e0150757.
Featured image is in the public domain, available on Wikimedia commons.