A couple of years ago I was investigating the work of TDA Lingo (deceased) through one of his students, Neil Slade. TDA Lingo worked with the theory that a vast number of dormant brain functions reside in the frontal lobes and can be activated to some extent by certain techniques. Neil himself describes his anecdotal experiences of psi phenomena, astral travel, enhanced intuition etc. as a result of progressing towards what he describes as a 'frontal lobes transcendence', which he equates with the religious or mytical peak experiences described by many cultures. After trying such techniques, which involve using imagery to directly stimulate the amygdalae of the limbic system (the root of the theory lies in the fact that these structures act as a sort of switch between the advanced parts of the brain and the more primitive 'reptile brain' - this being a very simplified description if you happen to know about the frontal lobes), I have had some absolutely astonishing, intense experiences.
Neils website is found at www(dot)neilslade(dot)com, where what he would consider the essential information is provided free.
I have since left this research after becoming entirely consumed with an even more fascinating website, no prizes for guessing which one, but it has left me with the firm impression that we only use a small fraction of our brain's potential. It is the significance and implications of that fact which has since changed for me.