Hemi-Sync is a trademarked brand name for a patented process used to create audio patterns containing binaural beats, which are commercialized in the form of audio CDs. Interstate Industries Inc., created by Hemi-Sync founder Robert Monroe, is the owner of the Hemi-Sync technology.
Hemi-Sync is short for Hemispheric Synchronization, also known as brainwave synchronization. Monroe claimed that the technique synchronizes the two hemispheres of one's brain, thereby creating a 'frequency-following response' designed to evoke certain effects. Hemi-Sync has been used for many purposes, including relaxation and sleep induction, learning and memory aids, helping those with physical and mental difficulties, and reaching altered states of consciousness through the use of sound.
The technique claims to involve using sound waves to entrain brain waves. Monroe has claimed that, listening with headphones, brains respond by producing a third sound (called binaural beats) that encouraged various brainwave activity changes. Binaural beats generally have been widely studied for possible mental health therapies, outside of Monroe's products.
Studies have produced mixed results on the effectiveness of the claimed benefits for Hemi-Sync. In 2002, a University of Virginia presentation at the Society for Psychophysiological Research examined Monroe's claim. The presentation demonstrated that EEG changes did not occur when the standard electromagnetic headphones of Monroe's setup were replaced by air conduction headphones, which were connected to a remote transducer by rubber tubes.  Replicated, double-blind, randomized trials on anesthetized patients from 1999 have found Hemi-Sync effective as a partial replacement for fentanyl during surgery. However, a similar study from 2003 found it ineffective at replacing propofol however.
- Brainwave synchronization
- Binaural beats
- Mind machine
- Human enhancement
- Intelligence amplification
- Isochronic tones
- Neural oscillations
- Evoked potential
- Event-related potential
- Induced activity
- Lucid dreaming
- Ongoing brain activity
- Brainwave entrainment
- The Monroe Institute
- Altered state of consciousness
- US Patent 3884218: "Method of inducing and maintaining various stages of sleep in the human being"
- US Patent 5213562: "Method of inducing mental, emotional and physical states of consciousness, including specific mental activity, in human beings"
- US Patent 5356368: "Method of and apparatus for inducing desired states of consciousness"
- Stephen Barling, "Cosmic degrees: Out of body at The Monroe Institute". The Hook. February 13, 2003.
- "". The Effects of Hemi-Sync on Electrocortical Activity, Sadigh and Kozicky
- Chaieb L, Wilpert EC, Reber TP, Fell J. Auditory beat stimulation and its effects on cognition and mood States. Front Psychiatry. 2015 May 12;6:70. doi: 10.3389/fpsyt.2015.00070. PMID: 26029120; PMCID: PMC4428073.
- Le Scouarnec RP, Poirier RM, Owens JE, Gauthier J, Taylor AG, Foresman PA. Use of binaural beat tapes for treatment of anxiety: a pilot study of tape preference and outcomes. Altern Ther Health Med. 2001 Jan;7(1):58-63. PMID: 11191043.
- Wiwatwongwana D, Vichitvejpaisal P, Thaikruea L, Klaphajone J, Tantong A, Wiwatwongwana A; Medscape. The effect of music with and without binaural beat audio on operative anxiety in patients undergoing cataract surgery: a randomized controlled trial. Eye (Lond). 2016 Nov;30(11):1407-1414. doi: 10.1038/eye.2016.160. Epub 2016 Oct 14. PMID: 27740618; PMCID: PMC5108018
- Padmanabhan R, Hildreth AJ, Laws D. A prospective, randomised, controlled study examining binaural beat audio and pre-operative anxiety in patients undergoing general anaesthesia for day case surgery. Anaesthesia. 2005 Sep;60(9):874-7. doi: 10.1111/j.1365-2044.2005.04287.x. PMID: 16115248.
- Chandra Stone, Phyllis Thomas, Dennis McClain-Furmanski, & James E. Horton (2002). "EEG oscillations and binaural beat as compared with electromagnetic headphones and air-conduction headphones", Psychophysiology vol 39, pp. S80
- Kliempt P, Ruta D, Ogston S, Landeck A, Martay K (August 1999). "Hemispheric-synchronisation during anaesthesia: a double-blind randomised trial using audiotapes for intra-operative nociception control". Anaesthesia. 54 (8): 769–73. doi:10.1046/j.1365-2044.1999.00958.x. PMID 10460529.
- Lewis AK, Osborn IP, Roth R (February 2004). "The effect of hemispheric synchronization on intraoperative analgesia". Anesthesia and Analgesia. 98 (2): 533–6, table of contents. doi:10.1213/01.ane.0000096181.89116.d2. PMID 14742401.
- Dabu-Bondoc S, Drummond-Lewis J, Gaal D, McGinn M, Caldwell-Andrews AA, Kain ZN (September 2003). "Hemispheric synchronized sounds and intraoperative anesthetic requirements". Anesthesia and Analgesia. 97 (3): 772–5. doi:10.1213/01.ane.0000076145.83783.e7. PMID 12933400.