Specifically, what do Sri Aurobindo and The Mother explain regarding these experiences and their place in sadhana?
Breath is only one form of vehicle, a main one, through which prana enters into the physical system for providing energy to the body. The physical breath itself does not as such enter the brain as the energy does.
However, there are other sources of energy as well, from the world around us, from above as well as below.
Virya is the spiritual energy that enters from above. It develops if the sexual energy, called retas, is conserved. By mastery over sex, not only the act but in thought and impulse, retas gets transferred into tejas, vital energy and then ojas, intellectual energy and, finally veeryas, spiritual energy.
Yes, there are two well-known pranic currents that act upon opposite sides of the brain with cooling and heating effects, respectively. A third, which is generally asleep but wakes up by yoga, is the middle one, which balances the two and uplifts them further.
Sri Aurobindo and The Mother have written about these things, but this is not the main hinge of their yoga, which relies mainly on psychological processes such as aspiration, rejection, faith, sincerity, surrender and most of all, psychically opening to the Mother. Mechanical and psychophysical processes are, in general, not part of this yoga. Mechanical methods carry an intrinsic risk of destabilising if the nerves are not strong and ready.
Affectionately,
Alok Da
