Brainwave entrainment or "
brainwave synchronization," is any practice that aims to cause
brainwave frequencies to fall into step with a periodic stimulus having a frequency corresponding to the intended brain-state (for example, to induce sleep), usually attempted with the use of specialized
software. It purportedly depends upon a "frequency following" response on the assumption that the human brain has a tendency to change its dominant
EEG frequency towards the frequency of a dominant external stimulus.
[citation needed] Such a stimulus is often aural, as in the case of
binaural or
monaural beats and
isochronic tones, or else visual, as with a
dreamachine, a combination of the two with a
mind machine, or even
electromagnetic radiation.
[citation needed]
[edit] History
Enthusiasts of brainwave entrainment claim that it has been noted or used in one form or another for centuries (long before the invention of EEG equipment), from shamanistic societies' use of drum beats to
Ptolemy noting in 200 AD the effects of flickering sunlight generated by a spinning wheel. In the 1930s and '40s, with then-new EEG equipment and strobe lights,
William Grey Walter performed some of the first scientific research on the subject.
[1] Later, in the 1960s and '70s, interest in altered states led some artists to become interested in the subject, most notably
Brion Gysin who, along with a Cambridge math student, invented the
Dreamachine.
[2] From the 1970s to date there have been numerous studies and various machines built that combine light and sound. These efforts were aided by continued development of micro-circuitry and other electronic breakthroughs which allowed for ever more sophisticated equipment. One of the more frequently noted scientific results claimed for brainwave entrainment was the discovery of binaural beats, published in
Scientific American in 1973 by Gerald Oster.
[3] However, Oster's research actually makes no mention of brainwaves. With the development of isochronic tones by Arturo Manns, combined with more sophisticated equipment, these discoveries led to many attempts to use claimed brainwave entrainment techniques in the treatment of numerous psychological and physiological conditions.
[edit] Aural entrainment
[edit] Binaural beats
Main article:
Binaural beatsBinaural beats deserve special mention because of the manner in which the desired frequencies are obtained. Brainwave
entrainment may be achieved when
audio signals are introduced to the brain causing a response directly related to the frequency of the signal introduced, called
binaural beats. Two tones close in frequency generate a
beat frequency at the difference of the frequencies, which is generally
subsonic. For example, a 495 Hz tone and 505 Hz tone will produce a subsonic 10 Hz beat, roughly in the middle of the alpha range. The "carrier frequency" (e.g., the 500 Hz in the example above), is also said by some to affect the quality of the transformative experience.
[citation needed] Note that this effect is achieved without either ear hearing the pulse when headphones are used. Instead, the brain produces the pulse by combining the two tones. Each ear hears only a steady tone. Although some have claimed that these frequencies do provide help in treating certain medical conditions,
[4] there is not a wide acceptance by the medical community to adopt the practice of brainwave entrainment for emotional/mental disorders. A fixed, constant frequency of synchronization is less helpful than techniques such as classical
neurofeedback or learning
meditation, which naturally generate brainwave frequencies that differ from person to person and may vary from minute to minute.
[citation needed]
[edit] Monaural beats
Binaural beats were first discovered in 1839 by H. Dove, a German experimenter. At that time, binaural beats were considered to be a special case of
monaural beats. Binaural beats are not the same as monaural beats. Binaural beats are perceived by presenting two different tones at slightly different pitches (or frequencies) separately into each ear. This effect is produced in the brain, not in the ears as with monaural beats. It is produced by the neural output from the ears and created within the olivary body within the brain, in its attempt to "locate" the direction of the sound based on phase.
[5]
Only monaural beats are the result of the arithmetic (vector) sum of the waveforms of the two tones as they add or subtract from one another, becoming louder and quieter and louder again.
[5]
Monaural and binaural beats are rarely encountered in nature, but in man-made objects, monaural beats occur frequently. For example, two large engines running at slightly different speeds will send "surges" of vibrations through the deck of a ship or jet plane. The lower pitched tone is called the carrier and the upper tone is called the offset.
[5]
Monaural beats occur in the open air and external to the ears. For example, when two guitar strings of slightly different frequencies are plucked simultaneously, monaural beats strike the ear as beats and therefore excite the thalamus, an action crucial for entrainment.
[citation needed] Binaural beats played through loudspeakers become monaural beats.
[5]
To hear monaural beats, both tones must be of the same amplitude. However binaural beats can be heard when the tones have different amplitudes. They can even be heard if one of the tones is below the hearing threshold. Noise reduces the perceived volume of monaural beats whereas noise actually increases the loudness of binaural beats.
[6]
[edit] Isochronic tones
"Isochronic tones are evenly spaced tones which turn on and off quickly."
[7]
[edit] Audio–visual entrainment
Audio–visual entrainment (AVE), a subset of brainwave entrainment, uses flashes of lights and pulses of tones to guide the brain into various states of brainwave activity. AVE devices are often termed light and sound machines or mind machines. Altering brainwave activity may aid in the treatment of psychological and physiological disorders.
[edit] See also
- ^ http://www.stanford.edu/group/brainwaves/2006/theclinicalguidetosoundandlight.pdf
- ^ Allen, Mark (2005-01-20). "Décor by Timothy Leary". The New York Times. http://www.nytimes.com/2005/01/20/garden/20mach.html?ex=1264050000&en=2ead60550b324624&ei=5088&partner=rssnyt. Retrieved 2010-04-26.
- ^ http://rawexplorations.com/sites/default/files/G%20Oster%20-%20Auditory%20Beats%20in%20the%20Brain.pdf "Auditory Beats in the Brain," Gerald Oster, 1973
- ^ The Clinical Guide to Light and Sound, Thomas Budzynski, PhD
- ^ a b c d Entraining Tones and Binaural Beats, Dave Siever
- ^ Oster, G. (1973). Auditory beats in the brain. Scientific American, X, 94–102.
- ^ Entraining Tones and Binaural Beats, David Siever
[edit] External links
Electrical activity in the brain is rhythmic. The frequency of this rhythm depends on the state the brain is in: an active, alert state correlates to rhythms in the range of 30-100Hz. As brain activity reduces in frequency, so the brain state changes: 8-12Hz is associated with relaxation, 4-7Hz with meditation, and below 4Hz indicates deep sleep.
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