A visitor asked:
V. What meditation (dhyana) is the best?
Bhagavan. The best meditation is that which continues in all the three states. It must be so intense as not to give room
even to the thought “I am meditating”. As waking and dream states will thus be fully occupied by it, deep sleep may also be deemed to be an undifferentiated dhyana.....
V. What is the difference between sushumna nadi and atma nadi?
Bh. Sushumna is the central nadi which functions in the practice of yoga, that is, in dynamic dhyana and for the attainment of siddhis (psychic powers) and which the
yogis claim to end in the sahasrara, the brain.
Atmanadi, Paranadi or Amritanadi is the force current which rises from Heart to the sahasrara in the static dhyana of the jnana marga, which leads to Self-realisation. Sushumna has finally to merge in the Atmanadi which supports it.
The nadis are the nervous system along which consciousness flows from Heart to the whole organism.
~ GURU RAMANA. Chapter: MEDITATION.