Among the more widely known facts are EEG-research programs
, that proved a resonance-like rapport of brain waves upon external
optical or acoustic stimulation. The brain's own frequencies tune in
with the frequencies of the stimulus, an effect called "photic driving"
or "frequency following response" (ffr). Some frequency spectrums
and areas are associated to psycho-physical states (and Greek letters),
but these measurements do not seem apt to really cover the complex
wave activities of the brain, and they
only offer a vague outline of a theory of psycho-physical music.