Whether it's a form of japa meditation such as TM or a form of concentration as in Kriya Yoga the objective is to *move the prana up the spine*. In TM the objective is achieved by effortless control of the mind, in Kriya Yoga it is the direct control of the prana using concentration.
Consciousness is the 'rider' of prana; effect prana=effect consciousness. As the prana goes up the spine the consciousness or jiva does likewise giving rise to astral phenomenon such as bells, harps, buzzing and other sounds associated with each chakra, which are the sounds of the mechanics of each chakra. When the prana reaches the 6th chakra, the jiva or soul experiences the first state of Enlighenment or Savikalpa Samadhi as MMY himself says in his lecture on kundalini.
