Here is an interesting article I found on Meditation.
In the ancient Indian text of the Yoga Sutras 1:2, Patanjali explains; "Yoga is the regulation and cessation of fluctuations and changes which are ordinarily expressive in the conditioned field of consciousness." The purpose of meditation (concentration methods) is to still thought processes by calming the mind. This enables the meditator to experience pure consciousness without the interruption of the waves of mental activity and thought. As the meditator assumes a relaxed body posture with the spine erect, the flow of CSF up and down the spine is enhanced. Then by focusing one's attention between and above the eyebrows, CSF is encouraged to move up into the area of the optic cistern, a reservoir of CSF in the same anatomical area as the "third eye" center.
Meditative techniques such as "mantras", and "kirtan" (chanting) are also utilized to help the practitioner experience pure awareness without the interruption of thoughts or feelings. A "mantra" is a word, sound or word-phrase, which the meditator concentrates upon to keep attention from being involved with the external physical environment, physical feelings, moods, or thought processes. "Mantras" are mentally repeated and/or "listened to" in reiterated cadence, usually in coordination with, and simulating the audible sound of the in-going and out-going breath. As the "mantra" is coordinated with the in and out going breath, the practitioner's attention is focused on the cerebrospinal fluid going up and down the spine.
Chanting involves repeating aloud, over and over again, a certain specific series of Sanscrit or English words about some aspect of God. The chants are short, reiterated affirmations that reinforce the purpose of meditation, which is to experience pure consciousness or God. Chanting is also another method utilized to help remove the meditators attention from thought processes or moods as the practitioner concentrates on the sound of the chant rather than mental activity.
The high and low pitch "tones" of the chant resonating within the body also enhance CSF flow. This occurs because the vibrational sound of the chant has a stimulating effect on the liquid medium of the CSF as it circulates around the brain and spinal cord. Lower pitch "tones" resonate in the chest and abdomen areas, and effect the CSF within the spinal column. Higher pitch "tones" resonate in the head, and therefore impact on the CSF as it circulates within the cranium.
Thus, as the yogi or yogini practice physical postures (asanas), breath techniques (pranayamas), and concentration methods (meditation), the overall circulation of cerebrospinal fluid is greatly enhanced, and thereby the functioning of the all important neuropeptides. These powerful body chemicals may also play a role on the physical level in the overall goal of yoga practice to experience God consciousness on the spiritual level.