Yoga for Mental Health- a Neuroscience Perspective

12/08/2020

The ancient practice of yoga has expanded to all corners of today's world. Recently it has gained popularity in the west, for example, the number of Americans practising yoga was reported to have risen by 50% between 2012 to 2017. While some may argue that this rapid expanse has led to distortion of the spiritual focus of yoga from it's origins, I feel that in a world dominated by stress, this is does not matter. Whether somebody's intention before they arrive on the mat is to ascend into the cosmos, or simply to tone their butt, they are slowing down and breathing deeply and, in turn, cultivating the tools to hack ones own nervous system and wellbeing.  Modern western yogis  may begin their journey for physical benefits and down the path reap mental improvements. As someone who is interested in the brain, I want to know the science underlying such mental benefits and what this means yoga can offer for global issues surrounding mental health.

So, what defines yoga? The word yoga is derived from the Sanskrit (ancient Indian language) word 'Yuj' meaning to unite. The union of yoga is classically thought as the union of ones individual consciousness with universal divine consciousness. The defining text of classical yoga is the Yoga Sutras, written by Indian philosopher Pantajali, which outlines an eight-limbed path to achieving a meaningful and spiritual life through yoga. Only one of these eight limbs is 'asana', meaning the physical practice, and in the text outlines little more than a seated position for a prolonged meditation. Equally important to physical control of the body is the control of behaviour, breath, senses and focus. So although your hamstrings will benefit for the many downward dogs you go through in a physical yoga session, unfortunately by classical yoga standards, these alone won't lead to spiritual enlightenment. However, breathing deep into postures and drawing the senses inwards will take you closer. In cultivating deeper practice, a yogi will find the host of mental benefits increases. Spiritually and neurochemically.


To investigate how yoga affects us mentally, it is important to look at physiology. The autonomic nervous system, the body's autopilot, is divided into two modes. These are the sympathetic 'fight or flight' mode, which prepares the body for action, and the parasympathetic 'rest and digest' mode, during which things like digestion, growth and repair are prioritised. In yoga and other meditative practices, the body tends to favour the parasympathetic nervous mode, with a low heart rate and slowed breathing. This is in contrast to the sympathetic nervous system where heart and breathing rate speeds up. The autonomic nervous system has nerves from the brain to the organs, controlling the activity of various organs in the body. Reciprocally, there are other nerves from our organs back to our brains, which provide the brain with sensory information about the external world. By conscious control of breathing, we change the sensory information coming from the lungs to the brain. In response to this sensory information, the brain enhances either the parasympathetic or sympathetic modes. The slow controlled breathing is one way yoga signals to the brain to increase the parasympathetic mode, and increases body restoration.

The sympathetic mode responses are largely meditated by a hormone molecule called cortisol. While the sympathetic nervous system functions to prepare the body for action in life-threatening situations, it can also be activated by non-threatening stress signals. A text from your boss, bank statements, exams, and any other aspect of stressful 21st century living can activate the sympathetic mode. The association between chronic stress and mental health problems has been investigated and evidence has showed high levels of cortisol may be a contributing factor to mood disorders such as depression. Experiments have demonstrated cortisol is capable of damaging nerve cells and switching on genetic instructions for cellular suicide, this may play explain how the molecule leads to symptoms of depression. Approximately one quarter of UK citizens experiencing mental health problems at some point in their lifetime. The many stresses we face in our modern world could explain why society faces high risks of mental health problems, by sustaining an unnaturally over-active sympathetic nervous system and causing cortisol-induced nerve cell damage. 

So, where does yoga fit in? Yoga often depresses sympathetic mode activity while enhancing the parasympathetic mode - which could mean that yoga decreases cortisol levels, preventing cortisol-induced damage. Neuroscientist, Thirhalli, and colleagues conducted an experiment on patients with depression and found that after four weeks of regular yoga practice, blood cortisol levels decreased which correlated with a decrease in depressive symptoms. This may provide insight into our current mental health treatment plans.  Antidepressant medication has shown to be ineffective in up to thirty percent of patients and cause negative side effects as well as unpleasant withdrawal symptoms. Encouraging patients to get involved with yogic and meditative practices, alongside psychological therapy, may be a good idea before immediately prescribing medication.


Beyond decreasing cortisol levels, yogic practices have shown to have other beneficial mental effects. One experiment demonstrated that yogic breathing techniques could increase levels of nerve growth factor (NGF)-a molecule involved in growth of new nerve cells and repairing damaged nerve cells, and is deficient in neurodegenerative disorders such as Alzheimer's disease. Other experiments have shown yoga practice can increase levels of oxytocin - a molecule key in social functioning and is deficient in schizophrenic patients. Much of the western world holds their faith in science and have far much more trust in a chemical compound administered by a psychiatrist than in spiritual practice. However, with further research, science is proving that spirituality may have something to offer in terms of mental health for, not only improved wellbeing, but also treating a variety of disorders. Perhaps yoga alone may not account for a full treatment, but the healing neurophysiological effects are something clinical practitioners should be aware of and encourage in patients. When Patanjali comprised the yoga sutras in 400 BC, he was not writing with it in mind of potential therapies for Alzheimer's patients, but this does not mean modern medicine cannot learn from these practices.

Although modern Western yoga may be a total distortion from its roots, this should not discredit the fact that people are engaging in a practice that is good for their general physical and mental health. Science and spirituality can learn from each other and I for one think that the rise in yoga practice in a world dominated by stress, where mental health problems are on the rise, is an excellent thing.