- Brainwave synchronization
Brainwave synchronization or "brainwave entrainment," is any practice that aims to cause brainwave
frequencyto 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.
Brainwave synchronization with binaural beats is said to help 'synchronize the two hemispheres of the brain', hence the
Hemi-Sync(by Monroe Institute) example product. There is dispute over the efficacy of the practice.
It is also a private case of functional
brainconnectivity concept, whereas functional connectivity is defined as the temporal correlationbetween spatially-remote neurophysiological events, expressed as deviation from statistical independence (temporal correlation) across these events in distributed neuronal groups and areas, which produce the brainwaves. [for the recent review see Fingelkurts An.A., Fingelkurts Al.A., Kähkönen S. "Functional connectivity in the brain – is it an elusive concept?" Neuroscience & Biobehavioral Reviews. 2005, 28(8):827-836). As the authors have stated, "the functional brain connectivity has become one of the most influential concepts in modern cognitive neuroscience, especially given the current shift in emphasis from studies of functional segregation to studies of functional integration."]
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 frequencyat 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 mindof 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.Fact|date=February 2007 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, [ [http://www.stanford.edu/group/brainwaves/2006/theclinicalguidetosoundandlight.pdf The Clinical Guide to Light and Sound, Thomas Budzynski, Ph.D.] ] 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 neurofeedbackor learning meditation, also which naturally generate brain wave frequencies that differ from person to person and may vary from minute to minute.Fact|date=April 2008
Comparison of brainwave entrainment software
Ongoing brain activity
* [http://www.stanford.edu/group/brainwaves/2006/index.html Brainwave Entrainment to External Rhythmic Stimuli] - Interdisciplinary research and clinical perspectives symposium (Stanford University)
* [http://sica.stanford.edu/events/brainwaves/AuditoryDrivingRitualTech.pdf Auditory Driving] - Overview of sonic entrainment methods
* [http://switchedonbrainwaves.googlepages.com/ Switched on Brainwaves] - A site providing free binaural beats set to music.
* [http://gnaural.sourceforge.net/ Gnaural] - GTK+ Binaural-Beat generator (GNU GPL license)
* [http://uazu.net/sbagen/ SBaGen] - Binaural Beat Brain Wave Experimenter's Lab (open source)
* [http://www.meta-mind.de/MetaMind_Mind-Machine_binaural_beat_Brainwave_Lab MetaMind] - open source Java binaural Beat Brainwave Mind Machine software with optional EEG Neurofeedback
* [http://pantheon.yale.edu/~bbl2/GnauralJavaApplet_signed.html Java Binaural Beat Generator] - An example of binaural beats that runs in your browser
* [http://www.download.com/MultiFreq/3000-2051_4-8970998.html MultiFreq] - A free and versatile program for creating binaural beats
* [http://cryosleep.yellowcouch.org/ The cryosleep brainwave generator] A free program to generate brainwaves under Linux, demo sounds are online
* [http://www.download.com/Virtual-Light-Sound-Meditation-Machine/3000-2056_4-10813447.html?tag=lst-1/ Virtual Light & Sound Machine] Unique program simulates brainwave entrainment using flashes on computer monitor (Freeware).
* [http://www.i-dose.us/ I Dose] - Streaming Binaural Beats
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