The practice of khechari mudra (gesture of the tongue lock) exerts a controlling influence upon the network of endocrine glands throughout the body. This is achieved by regulating the production of the powerful secretions of the brain itself. These secretions are produced in tiny amounts to control the functions of the pituitary gland, thereby controlling the whole orchestra of glands associated with the centres below ajna. These dependent glands include the thyroid, mammary, thymus, adrenal and reproductive glands, as well as many other dependent processes which continually go on in the body.
Khechari mudra also influences the centres in the hypothalamus and brainstem which control involuntary actions such as autonomic breathing, heart rate, emotional expression, appetite and thirst. The hypothalamus has a strong connection with the thalamus and the RAS (reticular activating system), which assumes a vital role in the sleep and waking mechanisms and all degrees of central nervous system activities, including the ability to concentrate. The practice also influences the salivary gland and the faculty of taste, which are connected to the lower nerve plexuses involved in the digestive and assimilative processes, in turn allowing for some control over one’s sexuality. In Hatha Yoga Pradipika the effects on the body are described (3:38–39):
The yogi who remains with the tongue going upwards for even half a second is freed from toxins, disease, death, old age, etc. One who accomplishes this khechari mudra is neither troubled by diseases, nor death, lassitude, sleep, hunger, thirst or unconsciousness.
This sloka concerning the powerful effects of khechari mudra on human psychophysiology and destiny is better understood when one knows about certain neuroendocrinal functions of the brain. During the practice of khechari mudra, a number of pressure points located in the back of the mouth and the nasal cavity are stimulated. These points influence the whole body. As the tongue is inserted into the nasal cavity, many tiny nerve endings are activated that allow for greater autonomic control.
Even in normal life, with continuous practice of the simple version of khechari called nabho mudra, the sensations of hunger and thirst are reduced. One does not feel like eating or drinking and gradually the body adjusts accordingly. This can be experienced by experimentation.
Khechari mudra is just one example of how mudras, when practised properly for some time, can affect the physiology of the body and brain, in turn allowing access to parts of the brain and to human potentials that have previously remained dormant and unknown.