‘During activity the brain predominantly pulses in alpha and beta, or between twelve to thirty cycles per second. Theta is the zone of electrical activity the brain decelerates into right before sleep, or the delta state, when we pulse at between two to four cycles per second…Theta is that period of drifting right before sleep when all sorts of thoughts and memories wash through consciousness…’
This is from a book I am reading called 'Drumming on the Edge of Magic' by Mickey Hart. He is exploring the possibility that an altered trance-like state can be achieved by percussive sound, especially drumming.
'Drumming on the Edge' is a very interesting book; part biography, part history of the drum, part quasi-scientific study.