In the context of brain science: a distinctive brain-rhythm or brain-wave which occurs mainly in the occipital region of the cortex, and which is correlated, on the psychological level, with feelings of drowsiness, relaxation and disengaged attention on the part of the subject; it is of relatively high amplitude, and has a frequency range of between 8 and 13 Hz (Hertz, or cycles per second); of parapsychological interest as a possible physiological indicator of a psi-conducive condition in the subject. [From the Greek alpha, first letter of the Greek alphabet]