Through the simple mechanism of closing or opening one of the nostrils, the yogi has a wide array of techniques to control his moods and energies.

The quality of Prana processed through the two nostrils differs and corresponds with the qualities associated with the two sides of the brain. The nerves going out from the two brain hemispheres cross at the level of the eyebrows. The left hemisphere is connected to the right side of the body and right nostril; the right hemisphere to the left side of the body and left nostril.

We breathe predominantly through one nostril or the other at any given time. The dominant nostril alternates rhythmically every 90 to 150 minutes. The length of the cycle reflects universal rhythms, individual temperament, and the personal state of mental and physical balance. The rhythm itself is mediated mainly through structures in the hypothalamus and pituitary, though other areas in the brain are also involved.

You may use the technique of inhaling and exhaling exclusively through either the left or right nostril in order to benefit from the quality associated with that nostril. For instance, breathe exclusively through the left nostril to deal with compulsive eating habits.

Breathing through the left nostril is associated with:

Ida, the nadi which ends at the left nostril

Apana, the cleansing energy

The Moon energy—cooling, receptive

Calmness   

Empathy

Sensitivity    

Synthesis

Breathing through the right nostril is associated with:

Pingala, the nadi ending at the right nostril

Prana, the nurturing energy

The Sun energy—warming, projective