What is Brainwave Entrainment?

Brainwave synchronization or "brainwave entrainment," is any practice that aims to cause brainwave frequency to fall into step with a periodic stimulus having a frequency corresponding to the intended brain-state (for example, to induce sleep). It depends upon a "frequency following" response, a naturally occurring phenomenon where 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 beats, 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.

What are Binaural Beats?

Binaural beats deserve special mention because of the intriguing manner in which the desired frequencies are obtained. Brainwave synchronization (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 500 Hz tone and 510 Hz tone will produce a subsonic 10 Hz tone, roughly in the middle of the alpha range. The resulting subsonic tone may affect the state of mind of the subject. 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. 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, there is not a wide acceptance by the medical community to adopt the practice of brainwave synchronization for emotional/mental disorders. The fixed, constant frequency of the synchronization is less helpful than techniques such as classical neurofeedback or learning meditation, also which naturally generate brain wave frequencies that differ from person to person and may vary from minute to minute.

What Bilateral Sound?

Bilateral sound is a type of bilateral stimulation used in eye movement desensitization and reprocessing (EMDR) in the same manner as eye movement. It has been reported to enhance visualization and hypnosis, but this has not received attention in research. Essentially, the sound moves back and forth across the stereo field at a steady rhythm. In this regard, bilateral sound has been used in commercial recordings, and has been applied manually with the use of an electronic metronome or other means.

Source: Wikipedia
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