In the Bhagavad Gita (5:27,28), the Lord says:

“The muni controls his senses, mind, and intellect, removing himself from contact with them by neutralizing the currents of prana and apana in the spine, which manifest as inhalation and exhalation in the nostrils. He fixes his gaze in the forehead, at a point midway between the two eyebrows. Such a one attains complete emancipation.”

This stanza refers to Kriya Yoga, as Swami Kriyanandaji explains:

“Kriya Yoga is the science that was particularly recommended by my own Guru and by his line of gurus. Kriya Yoga was first given in modern times by the great Himalayan master known simply as Babaji (“Revered Father”)….

“Babaji told his disciple Lahiri Mahasaya, whom he initiated into Kriya Yoga in 1860, that Kriya is the supreme ancient science of yoga, and that he himself in a previous body had given it to the world. This science may be called God’s greatest gift to humanity for the soul’s salvation.

“Kriya Yoga helps one (as we discussed earlier in this book) to equalize the incoming and outgoing breaths, and to absorb ones energy in the spine, where one feels the currents as a cool (rising) and a slightly warm (descending) current.”