http://en.wikipedia.org/wiki/Precuneus

“I strongly suspect that it will eventually be discovered that deja vu and related phenomenon are associated with increased activity in the precuneus, and with a ‘partial transition into consciousness’ of effects related to the common functioning of episodic memory.

This may take some time to formalize as science, but if you were to experience a representation in your consciousness of the function of your own episodic memory, you would be both astonished and edified to discover that it is a kind of dreaming-marked-as-real-experience. And this marking, were it to emerge unlinked to its inner referents into consciousness, would catalyze the experience we call deja vu.

This function of memory is nothing like storage as we understand it. It does not work like a machine, at all. It is floridly expressive, and is constantly processing experience (in an utterly unexpected way) in the background of our waking consciousness. It’s real character, however, is more obvious in dreaming and poetry, and can be more or less directly encountered with hypnotic techniques or trance.

Part of the overwhelmingly fantastical effects of psychedelic drugs are almost certainly related to rendering aspects of the functioning of episodic memory accessible to expression in real-time consciousness; and the effect of this is a ‘trip’ of universally sophisticated proportions — the basic assets of mind are feeding back into themselves, and the result is a form of metaphoric propulsion not entirely unlike that of an engine that can recursively apply an aspect of its own thrust to acceleration.”

http://en.wikipedia.org/wiki/Precuneus