In our previous post, we covered the Neuroscience perspective of the importance of sleep, and what happens when we sleep. Before we discuss the next topics on sleep i.e. the stages of sleep and how Yoga helps in improving quality sleep, it is important to understand the neuroscience of brain waves – a measurable indicator of the state of mind.

Our brain has approximately 80 to 100 billion neurons, which communicate with each other by transmitting electrical impulses through neural connections. The brain waves are nothing but the electrical signals that are generated when neurons are firing and sending messages to one another. The quicker the neurons fire, higher will be the frequency of waves. And, more the number of neurons fire simultaneously, higher will be the amplitude. Depending on the frequency and amplitude, there are five main types of brain waves. There are no hard and fast rules about their functions – but in general, higher the frequency more alert and awake you are.

Mostly, you have different brain waves active at the same time. Certain waves may dominate at a given moment – depending on what you are doing and what your mental state is. Also, certain waves dominate a certain part of the brain.

1. Lowest frequency waves (of relatively high amplitude) are the Delta waves (0.5 to 4 Hz) that are linked to a deep dreamless sleep. Here the person is in an unconscious state and loses bodily awareness. It allows the body and the mind to heal, regenerate/repair cells and relieve any pain. The level of stress hormone Cortisol decreases and the level of hormone Serotonin increases. Babies in the womb and infants are in this state. The Delta waves are also found in deep meditative states. The Delta waves are conducive to access unconscious mind.

2. Slightly faster are the Theta waves (4 to 7.5 Hz), which are often associated with deep relaxation – like in meditation. They are conducive to insight, intuition, creativity and inner peace. We may often enter such a relaxed state of consciousness when performing repetitive (and monotonous) activities like having a shower, watering plants, or even driving on the same route to reach a destination every day – your daily office commute. These waves are also generated when day-dreaming, imagining or fantasizing. In the state dominated by the Theta wave, the mind disengages itself from reality and focuses more on imaginative thinking – and hence it is the best time for creative ideas. With age, the intensity of the Theta waves in our brain decreases.

3. Next, are the Alpha waves (8 to 12 Hz) which are common when you are awake but very relaxed. You are in a state of relaxed wakefulness and tranquillity. You are physically and mentally relaxed with quietly flowing thoughts. This is conducive to stress reduction, focusing and learning. When in the alpha wave state, the heart rate and blood pressure decrease. The respiration rate decreases and becomes smoother. All of these responses are characteristic of the stimulation of the parasympathetic nervous system (relaxation response).

Restorative Yogasana poses are known to increase the Alpha wave activity – promoting relaxation. In inverted Yogasana poses, a Neuroscience reflex called “Baroreflex” causes stimulation of the baroreceptors located in the carotid sinus and the aortic arch increases the Alpha wave activity. The Alpha waves also increase when you have just finished an assigned task successfully.

In the restorative Yogasana session, the Alpha wave dominance can be easily achieved when there are very few or no external stimuli disturbing the brain. Any disturbance due to unexpected sensory disturbance may shift you out of the Alpha state and take you to normal wakefulness (dominated by the Beta waves – the next type of brain wave discussed below). You will see an experienced Iyengar Yoga teachers suggesting the use of crepe bandage over the head, ear and eyes while conducting restorative sessions for this specific reason – block the sensory stimulation. For a similar reason, while performing Savasana, it is recommended to have all sensory stimulation blocked:
o Visual – keep lights off and eyes closed with a blanket or eye pillow over the eyes
o Tactile (Touch) – fans off to block touch senses. avoid winds if doing Yoga in open
o Auditory (Sound) – windows closed to block outside noise
o Smell – avoid perfumes and strong smells
o Muscle excitation – avoid coughing, the motion of eyes, swallowing; and put bolster on thighs

It is to be noted that overstimulation of the Alpha waves can make you dull and lethargic, and also cause depression in an extreme situation. The remedy for depression in such a case is to perform Yogasana practice that stimulates the sympathetic nervous system (which triggers the Beta wave state) and makes your mind alert. Standing poses, Surya Namaskar and backbends, in particular, are useful in increasing the Beta waves.

4. Beta waves are higher frequency (12 to 40 Hz) and lower amplitude. They are present when you are awake, thinking about something and fully involved in some mental activity. This is a state of alert consciousness. When there is a dominance of the Beta waves, the mind is sharp and the person is able to think fast. Hence this state is conducive to problem-solving and decision-making. Beta waves are characteristic of the dominance of the sympathetic nervous system.

5. The smallest and fastest are Gamma waves (40 to 100 Hz) which manifest when you are deeply involved in something. This is the peak state of mental awareness and corresponds to moments in which focus and concentration are at their highest levels. This is conducive to learning and memory recall.

Neurologically, sympathetic nervous system stimulation is associated with increased Beta wave activity of the left cerebral hemisphere, and parasympathetic stimulation is associated with increased Alpha wave activity of the right cerebral hemisphere.

It is at a very early stage, but there is some research that suggests that the brain waves can actually change the biology of the brain. That means if you do certain Yoga postures, you would actually make certain neurological changes, and so, certain neurological diseases may get treated effectively. This is a separate topic which we will cover in one of our future posts.

In our next post, we will see how the brain moves successively from Beta->Alpha->Theta-> Delta – running a course of monotonically decreasing frequencies.

Also, if you have not done so far, read our most popular post on neuroscientific explanation on “why Yoga inversions are so effective for mental health”.