||This article needs attention from an expert in Neuroscience. (November 2008)|
Brainwave entrainment 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. Such a stimulus may be aural, as in the case of binaural or monaural beats and isochronic tones, photic (visual), as with a dreamachine, a combination of the two with a mind machine, or electromagnetic radiation.
Hemispheric synchronization, a potential and generally desired result of brainwave entrainment, refers to a state when the brainwave pattern of the right and left hemispheres become alike. A person with similar activity in both hemispheres is alleged (typically by companies trying to sell a product) to be happier, more optimistic, more emotionally stable and less prone to mental illness. Increased levels of synchronization are found naturally in people who meditate regularly and people who are very content with their lives in general.
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 waves range. The "carrier frequency" (e.g., the 505 Hz in the example above), is also said by some to affect the quality of the transformative experience. 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, there is not a wide acceptance by the medical community to adopt the practice of brainwave entrainment for emotional/mental disorders.
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.
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.[unreliable source?]
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.
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. Binaural beats played through loudspeakers become monaural beats. Binaural tones require headphones to be effective.
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.
"Isochronic tones are evenly spaced tones which turn on and off quickly."[unreliable source?] Unlike binaural and monaural beats, isochronic tones do not rely on the combination of two tones – the "beat" is created manually by turning a tone on and off.
Music Modulation and Audio Filtering
Modulating sound is a way to produce brainwave entrainment using something as complex as a musical track.[unreliable source?] In effect, this is "embedding" brainwave entrainment into the audio. Any sound can be used, from nature sounds to white noise to a full classical symphony.[unreliable source?]
Modulation works by rhythmically adjusting a component in the sound.[unreliable source?] For example, volume modulation would be used to increase and decreases the volume to create the rhythmic stimulus necessary for entrainment to occur.[unreliable source?]
The problem with modulation (above) is that it can often distort the audio, particularly when used with music or certain nature sounds like rain.[unreliable source?] Frequency band selection solves this problem by selectively modulating certain parts of an audio file, instead of the whole of it.[unreliable source?]
The brainwave entrainment is embedded into a lower frequency range only – affecting parts of the bass, but leaving the mid and treble alone.[unreliable source?] Frequency band selection can be used to affect only one part of a sound file.[unreliable source?] Multiple frequency bands can also be selected.[unreliable source?]
Frequency band selection is an important advancement, allowing entrainment to be embedded into any sound file with virtually no negative effect on the existing audio.[unreliable source?] Because it allows for much higher intensity levels, the effectiveness of the session is actually increased.[unreliable source?]
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.
- 1959 - Chatrain, G., Perterson, M., & Lazarte, J. - Demonstrated that "clicks" produced auditory driving.
- 1959 - William Kroger & Sydney Schneider - Produced "Brainwave Synchronizer" to induce hypnosis in dental patients for anesthesia and short procedures - Used photic stimulation and suggestions. 78% of subjects entered light to deep stages of hypnosis within 6 min. when using strobe. Study also showed that "expectation" played an important role in attainment of trance state.
- 1973 - Gerald Oster - Demonstrated that binaural beats produced much smaller evoked potential and concluded they were of little value in Audio Evoked Response. However, they could be of great use in developing a hypnotic altered state or a deeply relaxed state. Gerald Oster, Scientific American, October 1973, pp 94-102
- 1976 - Nogawa, T., Katayama, K., Tabata, Y., Oshio, T., & Kawahara, T. - Photic Stimulation Study - Reviewing EEG while giving photic stimulation.
- 1981 - Arturo Manns - Investigated isochronic tones. 15-minute sessions of isochronic tones followed by 15-min of biofeedback for bruxism (clenching of jaws, grinding teeth). Isochronic tones produced much better muscle relaxation. "The Application of Audio Stimulation and Electromyographic Biofeedback to Bruxism and Myofascial Pain-Dysfunction Syndrome." Oral Surgery, Vol 52, No 3, 247-252
- 1985 - G. Solomon - Reported 24 participants were treated with photic stimulation between 5 – 8 Hz for headache and migraine headache. 14 of 15 participants with sustained headache had complete relief. 5 of 6 with chronic headache had complete relief. 4 had no change. "Slow wave photic stimulation in the treatment of headache--a preliminary report." Headache. 25, 444-446.
- 1987 - Joseph Glickson - Exposed 4 subjects to photic stimulation at 6, 10, and 18 Hz. Study concluded that photic stimulation provoked an altered state of consciousness.
- 1989 - D. Anderson - Used red LED photic stimulation and variable frequencies controlled by patient to alleviate migraine headaches, even though migraine patients typically light sensitive. 60 patients in study. 7 suffered migraines through the entire study period. 49 of 50 migraines patients were suffering from were relieved by photic stimulation. Anderson DJ. (1989) The treatment of migraine with variable frequency photo-stimulation. Headache. 29(3):154-155
- 2000 - Joyce, Siever & Twittey - Investigated an Audio Visual Entrainment program for treatment of behavior disorders in a school setting, specifically Attention Deficit Disorder. Stimulated a beta frequency (18 Hz or higher) into left hemisphere and 12 Hz frequency into right hemisphere of brain using a field independent eye-set. Substantial improvements in attention and reaction time, reduced impulsiveness were demonstrated.
- Bilateral sound
- Binaural beats
- Comparison of brainwave entrainment software
- Emotiv Systems
- Event-related potential
- Evoked potential
- Human enhancement
- Induced activity
- Intelligence amplification
- Mind machine
- Music therapy
- Neural oscillations
- Ongoing brain activity
- Trancranial alternating-current stimulation
- Ochs, L (2007). "The low energy neurofeedback system (LENS): theory, background, and introduction". Journal of Neurotherapy: Investigations in Neuromodulation, Neurofeedback and Applied Neuroscience 10 (2–3): 5–39. doi:10.1300/J184v10n02_02.
- Budzynski, Thomas. "The Clinical Guide to Light and Sound" (PDF). stanford.edu.
- Siever, Dave. "Entraining Tones and Binaural Beats" (PDF). mindalive.com.[unreliable source?]
- "Entrainment Methods". transparentcorp.org. Transparent Corporation.
- Oster, Gerald (1973). "Auditory beats in the brain". Scientific American (229,4). pp. 94–102.
- Brainwave Entrainment and Marketing Pseudoscience
- Auditory Driving as Ritual Technology: A Review and Analysis – Overview of entrainment techniques
- Brainwave Entrainment to External Rhythmic Stimuli – Interdisciplinary research and clinical perspectives symposium (Stanford University)
- Virtual Light & Sound Machine Psychologist simulates visual brainwave entrainment using flashes on computer monitor.