It could be the single most important nerve in the body. The vagus nerve stretches from deep within the brainstem all the way into the belly. Literally the mind-body connection, it’s the cabling behind your "gut instincts." One doctor refers to the vagus nerve as the inner eye.

Just recently the FDA approved a surgically implanted machine that will periodically stimulate the vagus nerve to treat depression. The treatment boasts remarkable success. But don't worry; you probably don't need surgery. Practitioners of yoga may already be enjoying the benefits of vagus nerve stimulation.

The vagus nerve supplies motor and sensory parasympathetic fibers to virtually everything from the neck down to the first third of the transverse colon. Governing things like the heart rate, digestion, sweating, and skeletal muscles, it's easy to see how any basic yoga routine can stimulate this pivotal channel between the mind and body.

But it turns out that the vagus nerve is involved with many other, less obvious activities associated with yoga, like chanting and pranayama.

The acts of chanting, both listening and vocalizing, stimulate the vagus nerve through muscle movements in the mouth, like those important to speech and those that work the larynx for breathing. The nerve also connects to vocal chords and receives some sensation from the outer ear; thus the acts of vocalizing and listening can influence it.

But the most refined practice for yogic stimulation of the vagus nerve may be pranayama, the fourth step outlined in the Indian sage Patanjali's "Yoga Sutras." Also known as breath control, the exercises often involve synchronizing chanting, naval gazing, and breathing.