Yoga is a mind-body fitness practice combining muscular activity with a mindful focus on breathing, self-awareness, and energy. The National Institutes of Health classifies yoga as a form of Complementary and Alternative Medicine (CAM). 

Meditation and yoga can have many positive effects on brain health, including: 

• Improved brain chemistry: Yoga can increase endorphins and gamma-aminobutyric acid (GABA), which can improve mood and reduce anxiety. Meditation can help balance neurotransmitters, which are chemicals that relay information between neurons. 
• Reduced stress: Yoga can help activate the parasympathetic nervous system, which can lower the body’s stress hormones. Meditation can reduce activity in the limbic system, the part of the brain that controls emotions. 
• Improved focus: Meditation can help improve attention span and mental clarity. Yoga can help centre attention and sharpen concentration. 
• Reduced brain shrinkage (atrophy)
  Yoga may help slow the natural ageing process by lowering brain shrinkage in areas that process information and store memories. 
• Improved sleep. Meditation can help enhance the quality of sleep and shorten the time it takes to fall asleep. 
• Reduced pain
  Meditation can help reduce pain and boost emotion regulation. 
• Reduced blood pressure. Regular meditation can help lower blood pressure, reducing strain on the heart and blood vessels. 
• Improved mental health
  Yoga can help improve mental well-being and relieve chronic stress patterns. Meditation can help with mental health issues like social anxiety, obsessive-compulsive behaviors, and depression. 
  When you do yoga, your brain cells develop new connections, and changes occur in brain structure and function, resulting in improved cognitive skills such as learning and memory. Yoga strengthens parts of the brain that play a crucial role in memory, attention, awareness, thought, and language.

Meditation and Yoga techniques are receiving increased attention throughout the world, due to the accumulation of evidence based research that proves the direct and indirect benefits of such practices. Based on studies conducted so far, it has been found that the practice of meditation triggers neurotransmitters that modulate psychological disorders such as anxiety.

The art of meditation, once considered exclusively an Eastern practice often associated with religion and spiritualism, has become a more scientific modality in recent years and is accepted for routine practice in many parts of the world. No wonder Yoga Day is celebrated on 21 June all over the world.

The Indian government has recently allocated a Ministry with a budget to fund research in Yoga and Ayurveda. Recently, the benefits of Yoga have been well-recognized in the West. Harvard, MIT, and Yale universities have encouraged research on this new modality. The NIH has allocated a budget for this research as part of the National Center for Complementary and Alternative Medicine (NCCAM). 

A positron emission tomography (PET) CT scan has been used to compare the regional cerebral blood flow (rCBF).  The meditators have significantly higher rCBF in the prefrontal cortex (PFC) than the controls. The PFC is a brain region primarily responsible for executive functions such as decision-making and problem-solving ability.

EEG records the electrical activities of the brain. Alpha waves are generally associated with more relaxed and alert states of mind, and an experiment noticed that individuals clinically diagnosed with anxiety disorder displayed lower alpha wave activity. Theta oscillations assist with alertness and the ability to process information quickly. Research studies reported an increase in the alpha and theta activity in meditators. 

Transcendental meditation (TM) using mantras is a technique where the participants silently repeat a word or phrase. It helps to lower levels of anger, stress, depression and most importantly, anxiety.  Our brains do not contain fixed hardwiring; the neural pathways and circuits can in fact change with learning and with mental exercises, and meditation may be a harmless way to encourage the growth of new neurons (neurogenesis) along with the formation of new connections between existing neurons (synaptogenesis). By tying together the neurobiological effects of neurotransmitters, brain waves, mental exercise and the empirical evidence from the psychological experiments, it is evident that meditation is an effective treatment for anxiety, and it does not suffer from any side effects. It may also function as a preventive medicine; therefore, it is highly recommended to everyone and not limited to patients suffering from disease.

Ref: Meditation and Yoga can Modulate Brain Mechanisms that affect Behavior and Anxiety-A Modern Scientific Perspective, Divya Krishnakumar,1,2 Michael R Hamblin,3,4,5 and Shanmugamurthy Lakshmanan1,3,4.*Anc Sci. 2015 Apr; 2(1): 13–19.