It is a popular belief that the secret behind inverted Yoga poses (like Sirsasana and Sarvangasana) is the increase the blood supply to the brain that promotes relaxation and calmness. But it is not true. Then, what makes inversions so effective for mental health? It’s a body-mind Neuroscience reflex called “Baroreflex”. Let’s look at it from a neuroscience perspective.
Cerebral Blood Flow (CBF) is a measure of the blood supply to the brain in a given period of time. In an adult, CBF is typically 0.75 liters per minute. It is a popular belief that inversions increase the CBF which in turn promotes mental health. But this is not true. In fact, the human system is highly complex. It keeps very tight control of the homeostatic conditions of its most complex part – the brain, which requires a constant CBF in order to function properly. Too much blood (a condition known as hyperemia) can raise the pressure inside the skull (called intracranial pressure – ICP), which can compress and damage delicate brain tissues. And, too little blood flow (ischemia) can potentially result in damage or even death of brain cells.
How much the heart has to work to meet the brain’s demand for the blood depends on the position of the body. The gravity plays an important role in determining this. For example, while standing, the heart needs to be more active than while someone is sleeping or inverted. Also, it is imperative that the heart responds to any sudden changes in arterial pressure. This occurs, for example, when a person suddenly stands up from a sleeping position, or falls down while standing, or for some reason becomes inverted (like inverted Yoga poses). To handle such a complex work, a negative feedback system is present in the body that consists of pressure sensors (called Baroreceptors) and the autonomic nervous system (consisting of sympathetic and parasympathetic – covered in a previous post).
In Neuroscience terms, this feedback system is called the “Baroreflex” or “Baroreceptor reflex”. It is one of the body’s homeostatic mechanisms to help maintain CBF at nearly constant levels. The Baroreflex provides a rapid negative feedback loop in which an elevated blood pressure towards the head (e.g when you get into Sirsasana) reflexively causes the heart rate to decrease and also causes blood pressure to decrease. Similarly, any decrease in blood pressure (e.g. when you stand up) triggers the Baroreflex activation and causes the heart rate to increase, and to restore blood pressure levels.
Hence the brain needs to know the difference between the pressure at the head and at the heart, so that it can activate a proper autonomic response. To sense the pressure, the Baroreceptors are present in the neck in Carotid sinus, which is located at the original of Carotid arteries that deliver blood to your brain and head. The Baroreceptor are also located in the aortic arch to sense the pressure at the heart.
These Baroreceptors report the pressure through the cranial nerve to the brain. The brain, in turn, modulates the sympathetic and parasympathetic activities based on this pressure information from baroreceptors. The brain stimulates sympathetic activity when the pressure reported by the Baroreceptors at the neck becomes lower (when standing). Similarly, it increases parasympathetic activity when the reported pressure is high (in inversions). The idea is to bring back the homeostatic balance in such a way that the requirement of blood supply and pressure at the brain is met. It is important to note that factors other than the Baroreceptor pressure also may work to alter sympathetic vs parasympathetic response. For example, increased body temperature will act to increase sympathetic activity, as will feelings such as fear, anger, and anxiety.
The stimulation of Baroreceptors triggering parasympathetic relaxation response, as in inversions, also calms down Reticular Formation. This is an area in the Brainstem that filters the sensory signals. This lowers the level of excitation impulses from the sensory nerves – giving the state of inwardness. Reticular formation and its influence in Yogasana will be covered separately in a future post.
So, in all the inverted Yoga postures, the Baroreflex plays an important role in mental calmness and relaxation – as the parasympathetic nervous system gets stimulated and the heart is relaxed. This is a natural activation of the Baroreflex as the Carotid sinus Baroreceptors sense higher pressure because of the gravity pull. And, it is not because of the increase in CBF – as wrongly perceived.
The Baroreflex also plays a role in enhancing the relaxation the poses that use Jalandhara Bandha (also called Chin Lock). In Jalandhar Bandha, the chin is dropped into the sternal notch. This cervical flexion generates a mild local pressure on the Carotid sinuses that artificially throttles the flow of blood through the carotid arteries – triggering Baroreflex.
The yogic text Shiva Samhita has a clear mention of putting pressure on the carotid sinus nerves to experience a blissful state of mind. It mentions that such a stimulation slows down the heart, and the Vijnani Nadi (channel of consciousness) can be brought under conscious control.
The inverted poses that have Jalandhar Bandha Sarvangasana, Setubandh Sarvangasana, Halasana and Karnapidasana, produce profound relaxation and calmness because of enhanced Baroreflex caused by inversion as well as chin lock. When these poses are supported using props (as in Iyengar Yoga), they are highly restorative in nature. These supported poses are highly recommended because of their therapeutic nature to calm down the mind and the nervous system.
These inverted postures with Jalandhar Bandh are typically performed towards the end of the Yoga practice so as to promote relaxation response and cooling down. We have covered the need for “Cooling Down” in one of our previous posts titled “Why 20 minutes of cooling down is important in Yoga practice”.
In this post, we have not covered how inversions promote Diaphragmatic Breathing and how gravity helps lengthen the exhalations – which increase the calming effect on the mind. This is a topic worth a separate post.
It is advised to perform Yogasana (particularly inversions) mentioned in this post under the guidance of an experienced teacher or practitioner.