ACOUSTIC BRAINWAVE ENTRAINMENT 

Recent literature has suggested that acoustic brainwave entrainment techniques can produce beneficial physical and psychological effects that show the potential for therapeutic application (1).  The therapeutic use of acoustic brainwave entrainment is based on two hypotheses.  The first hypothesis is that brainwave frequencies, and/or amplitudes in certain frequency bands, can be modified by listening to, or "feeling" audible sound.  The second hypothesis is that the modification of brainwave frequencies in specified ways can have a positive effect on attention, relaxation, and hypnotic susceptibility to constructive suggestion and visualization. 

With respect to the first hypothesis, the use of sensory stimuli, such as auditory pulses (such as clicks or pops) (2), or flashing lights (3), to entrain specific cortical rhythms has been suggested in the literature.  A more subtle auditory approach, and one that is more conducive to cognitive therapy techniques, involves what is referred to as "binaural beats."    The existence of this phenomenon was first documented by Osler (4).  Essentially, when two auditory tones (below 1000 Hz and differing in frequency by 1 to 30 Hz) are introduced into each ear, an auditory brainstem response originates in the superior olivary nucleus of each hemisphere.  This response is perceived as an auditory beat.  For example, if a pure tone of 400 Hz is presented to the right ear, and a tone of 410 Hz is presented to the left ear (typically through headphones) a 10 Hz pulse is perceived by the listener.  There are several advantages to the use of the binaural beat effect in brainwave entrainment applications.  First, subtle pulses are perceived in the brain and are compatible with other techniques used in the sound for Healing process.  Next, sine wave frequencies in the audible range (i.e., above 20 Hz) can be used to generate perceived beats at frequencies below the audible range but relevant to brainwave frequencies (1-30 Hz).      

Recent research has suggested that the use of binaural beat techniques is also effective in the entrainment of brainwave frequencies.  For example, binaural beats at a frequency of 10.5 Hz have been shown to enhance the production of alpha brain waves that are associated with a relaxed and focused state. (5).  Listening to binaural beats at a frequency of 4 -7 Hz, indicative of a deep meditative state, has been shown to increase the production of theta brain waves (6).  The table below illustrates how different brainwave frequencies are associated with different brain processes.  Each brainwave frequency band is indicative of different levels of cognitive functioning.

          *Hz = Hertz, the unit of measurement that indicates how fast
brainwaves are cycling (frequency).  1 Hz = one wave per second.
Information in this table was adapted from (1).

Clinical Application 

There are also research results to support the second hypothesis that acoustic brainwave entrainment can have positive effects on attention and relaxation.  Recent studies have associated binaural beats with modification of cognitive function and emotional states. Binaural auditory beats in the beta range (i.e. associated with concentration and arousal) increased performance on a vigilance test (7).  In another study, binaural beat stimulation in the theta range (4-7 Hz) increased hypnotic susceptibility in low and medium susceptible groups (6).  In addition, listening to binaural beat tapes in the theta/delta frequency range (1-7 Hz) was shown to be beneficial in reducing mild anxiety (8). 

Acoustic Brainwave Entrainment as an Adjunct to the Sound for Healing Program 

An important aspect of the Sound for Healing process is to relax the body and quiet the mind.  One of the barriers to effective use of Guided Visualization techniques involves physical tension, hypervigilance, and low hypnotic susceptibility that often accompany disorders such as anxiety, depression and stress.  Acoustic brainwave entrainment is an effective tool in helping clients to relax and participate in the Sound for Healing process.

 References 

1. The Power of Sound, 2001, by Joshua Leeds, Healing Arts Press The High Performance Mind: Mastering Brainwaves for Insight, Healing, and Creativity, 1995, by Anna Wise, Tarcher/Putnam

2. Neher, A.  Auditory driving observed with electrodes in normal subjects. Electroencephalogrophy and Clinical Neurophysiology 13 (1961) 449-451.

3. Yagguchi, K and Iwahara, S.  Temporal sequence of frequency specific and nonspecific effects of flickering lights upon occipital electrical activity in man.  Brain Research 107 (1976) 27-38.

4. Oster, G.  Auditory beats in the brain.  Scientific American 229 (1973) 94-102.

5. Foster, DS. EEG and subjective correlates of alpha-frequency binaural-beat stimulation combined with alpha biofeedback.  TMI Research.  http://www.monroe-inst.com/research/alpha-binaural-beat.html

6. Brady, B and Stevens, L. Binaural beat induced theta EEG activity and hypnotic susceptibility.  The American Journal of Clinical Hypnosis.  24 (2000) 53-69.

7. Lane, JD, Kasian, SJ, Owens, JE, and Marsh, GR.  Binaural auditory beats affect  vigilance performance and mood.  Physiology & Behavior 63 (1998) 249-252.

8. LeScouarnec RP, Poirier, RM, Owens, JE, Gauthier, J, Taylor, AG and Foresman, PA. Use of binaural beat tapes for treatment of anxiety: a pilot study of tape preference and outcomes.  Alternative Therapies in Health and Medicine 7 (2001) 58-63.