Yoga and brain health • Dr. Silvia Mendel – brain researcher

Experts explain how yoga affects the structure and function of the brain

Yoga is an ancient health approach that involves the practice of mind and body through meditation, breathing and physical postures, which originates in Indian philosophy. This type of holistic approach has medical significance as it has the potential to improve physical and emotional dysfunction at the same time. Controlled experiments in humans have found a correlation between yoga practice and improvement in conditions of diabetes, cardiovascular functions and neuromuscular function. Also, there is evidence linking the practice of yoga and benefit in mental states such as anxiety, stress and depression and therefore, the studies tend to combine yoga as a complementary treatment for adults with clinical diagnoses.

In a meta-analysis type study (collecting and summarizing research papers that match predetermined eligibility criteria and statistical processing to summarize the results of the studies) conducted with the aim of investigating the immediate and long-term effects of yoga on the cognitive state in an adult population, a moderate effect was found on attention and concentration, speed of data processing and executive functions. 

In recent years, they began to examine how the practice of yoga affects the structure of the brain, such as differences in the thickness of the cerebral cortex and the volume of the gray and white matter, and on its function, with the help of brain imaging experiments and the performance of tasks and cognitive tests. In a meta-analysis scientific review published this month (December 2019) in the scientific journal Brain Plasticity, research leaders Gothe and Damoiseaux focused on 11 studies published between 2009-2019. They included each of the three elements of yoga practice: yoga postures, yoga-based breathing exercises, and yoga-based meditation exercises. Five of the studies involved people with no previous background in yoga practice who were recruited to a yoga class one or more times a week for a period of 10-24 weeks.

The other studies measured brain differences between people who regularly practice yoga and those who don't. The researchers used functional MRI (fMRI), MRI and SPECT (single-photon emission computerized tomography) to investigate how the brain structure changes among those with experience in yoga practice and to identify the areas and neural networks that were affected by short and long term practice.

The main findings of the review largely indicate a positive effect of yoga practice on the structure and/or function of the hippocampus, amygdala, cingulate cortex and brain networks such as the default network, whose activity is highest in states of rest, in which the person is awake but engrossed in thoughts or observation self Also, the studies reveal that the brain changes recorded in people who practice yoga are related to better performance in cognitive tests or measures of emotional regulation. For example, in tests that included exposure to an emotional experience, people who practice yoga showed higher activity of the prefrontal cortex, which reflects the ability to exercise cognitive control over emotional processes, compared to people who do not practice yoga. This could explain the reduction of stress, anxiety and depression among yoga practitioners.

The frontal cortex, a brain area located behind the forehead, is essential for planning, making decisions, performing tasks, and being able to choose the right option. Another particularly impressive result was recorded on the volume of the hippocampus. The study determined that the left hippocampus was significantly larger among yoga practitioners compared to the control group according to age, gender and fitness level. The hippocampus is involved in the formation and retention of short and long term memory and is known to shrink with age. This is also the structure damaged among the first in dementia and Alzheimer's along with the prefrontal cortex. 

The common denominator between yoga and aerobic activity 

The findings are extremely interesting and intriguing as they indicate that yoga improves many of those brain structures and functions that have been shown to have a significant effect from continuous aerobic exercise, Professor Gothe said. Yoga is not aerobic in nature, so there must be other mechanisms that lead to these brain changes, however, so far, there is no evidence to identify those mechanisms. For many years, researchers believed that from the moment a person reaches adulthood, the brain is unable to create new neurons and a process of continuous neuron loss begins throughout the years of life. But scientific evidence accumulated in the last 20 years shows that the adult brain can, in fact, produce new brain cells through a process known as neurogenesis. This phenomenon has been studied extensively in the context of physical activity, which has shown that a significant part of the neural tissue growth appears in an area known as the hippocampus.

In 1999 van Praag and his team discovered in a groundbreaking study that running mice on a wheel led to the birth of new neurons in the hippocampus. Given that the hippocampus is critical for memory formation and learning, the generation of new neurons created together with the increase in brain flexibility (synaptic plasticity) in this area, may explain the improvement in cognition and mood that accompanies physical activity. An increase in the flexibility of the brain means an increase in the number of connections between nerve cells called "synapses", which results in strengthening the communication between the neurons and improving the transmission and reception of external information. The aforementioned pioneering discoveries have opened the door to human studies with the aim of measuring the effects of physical activity on the structure and function of the brain and the relationship to improved cognitive performance and memory. Indeed, many studies show that physical activity also has positive effects on the human brain and may even help reduce the risk of Alzheimer's disease (See an earlier article, BDNF, the learning and memory vitamin).

Conclusions

Despite the paucity of studies and the fact that most of them are exploratory and it is not possible to conclude a definitive position about them, the evidence points to important brain changes associated with yoga practice. The amygdala, a brain structure that contributes to emotional regulation, tends to be larger in yoga practitioners than in non-yoga peers. Like the amygdala, the cingulate cortex is part of the limbic system, a circuit of structures that plays a vital role in emotional regulation, learning and memory.

Improving emotional regulation is key to the positive effects of yoga on the brain, reducing stress and anxiety. For example, studies link stress with shrinking of the hippocampus and poorer performance in memory tests in humans and animals. Therefore, the increase in the hippocampus tissue as a response to yoga has very significant consequences on the future cognitive state since a loss in its volume may impair memory. You can think of the brain like a muscle: the more you persevere, the hippocampus and the frontal cortex get stronger. why is it important? Because they are the two areas most exposed to dementia and cognitive decline in old age. It is true that dementia cannot be cured with the help of yoga practice, but it is possible to postpone the time of manifestation of the symptoms. 

Compared to traditional forms of aerobic training, yoga exercises can be an effective alternative for people with movement limitations, clinical diagnoses and especially for the elderly. Although the scientific evidence indicates that yoga is beneficial for brain function, more rigorous and controlled intervention studies are needed with a large enough number of participants being followed for long periods of time and the use of standardized methods that will enable the comparison of yoga practice with other types of physical activity. The researchers believe that the above will pave the way to identify the neurobiological mechanisms behind the benefit of practicing yoga.