There are two basic principles of the universe: prana shakti and chitta shakti, energy and consciousness. They are separate entities existing in duality, yet they are the opposite poles of the same principle. Thus, changes in the state of consciousness can be brought about by changes in the level of prana and vice versa. Tantra works on the principle that expansion of consciousness is specifically brought about by the liberation of energy. Therefore, even if one 'meditates' for one thousand years, if there is no liberation of energy then evolution of consciousness is not possible.
Although modern psychology cannot explain this process, the science of tantra has always known that the awakening of prana or the liberation of energy is the key to superconscious states.