This may play a role:
BETA: The most rapid is called a beta brain wave pattern, the pattern of normal waking consciousness. Beta is associated with concentration, arousal, alertness, and cognition. At its highest, most rapid levels, though, beta is associated with anxiety, disharmony, and unease.
ALPHA: Relaxed, brain wave activity slows into what is called an alpha brain wave pattern. Alpha patterns vary from deep alpha, a state of deep relaxation often referred to as the "twilight state" between sleep and waking, to the higher end of alpha which is a more focused yet still very relaxed state. Thus it is also referred to as the 'super-learning' state.
THETA: Slower still are theta waves. Theta is best known as the brain wave state of dreaming sleep, but it is also associated with a number of other beneficial states, including increased creativity, some kinds of "super learning," increased memory abilities, and what are called integrative experiences. "Ah-ha!" experiences, where you suddenly "get it," have an insight, are accompanied by bursts of theta waves in your brain.
DELTA: The slowest brain wave pattern is delta, the brain wave pattern of dreamless sleep.