Binaural beats is a simple to create and well-known auditory phenomenon among digital music producers. It is believed to entrain the brain and alter the consciousness in a host of different ways, but the scientifically support for such a belief has tended to be missing.
Binaural beats is the phenomenon in which sound with different frequencies fed at each ear result in an illusionary beat sound with the frequency of the difference between the frequencies presented at each ear. If in example a sine wave at 200 Hz is fed to the left ear and a sine wave of 210 Hz is fed to the right ear, the illusionary beat sound become 10 Hz . The belief that this can entrain the brain may be connected to the fact that brain waves operate at the same frequencies  as the illusionary beat sound tend do to, and that this may result in synchronization between the illusionary beat sound and the brain waves. This is an interesting hypothesis and if true may possibly be useful both for music producers as well as professionals in different disciplines.
In a systematic review published in 2015 , Chaieb, Wilpert, Reber and Fell concludes that binaural beats may have an effect on cognition and mood states, but that the evidences are inconclusive. The strongest points of evidence showed a tendency for binaural beats in the delta and alpha range to reduce anxiety. To get a more up-to-date state on the research on binaural beat, a rapid review on research literature from 2015 to 2018 was performed.
Literature Search Strategy
For this rapid review I searched the electronic databases Pubmed and Cochrane Trials, using the search term “binaural beats”. This resulted in 84 hits in Pubmed and 22 hits in Cochrane Trials, in which the abstracts where screened for relevance. Of this, accessible, original research articles in English from 2015 to 2018 with a primary focus on binaural beats was included. Studies that combined binaural beats with other brainwave entrainment technology, as in example monaural beats and light was excluded. Studies that was unclear as to what binaural beat stimulation was used was also excluded. Of the total of 106 studies found initially, 12 was included.
Most of the research literature found, reported an effect of binaural beat stimulation, but the research conditions (participants, length of binaural beat stimulation, and outcome measured) was highly disparate, which make it hard to come to any more conclusion than earlier reviews has done. However, some patterns and tendencies was found that may be of importance for further research.
Two of the studies reported individual differences in the results when participants was stimulated by gamma binaural beats. Ioannou, Pereda, Lindsen & Bhattacharya  found a difference in brain activity of musicians versus non-musicians when stimulated by gamma binaural beats at 40 Hz. Reedijk, Bolders, Colzato & Hommel  found a difference in attention of participants with low eye blink rate (EBR) versus high EBR when stimulated with gamma binaural beats at 40 Hz. Differences in cognition as a result of different EBR when stimulated by gamma binaural beats has also been reported before , which make it worth to consider for further research on binaural beats.
Six of the studies was done on students with a goal of exploring the positive cognitive perfomance effects binaural beats may have. Of these, four had a focus on gamma binaural stimulation at 40 Hz, and all found effects of relevance for learning. Reedijk, Bolders, Colzato & Hommel  found a difference in attention of participants with low EBR when stimulated by 40 Hz. Colzato, Barone, Sellaro & Hommel  found a decrease in global precedence effect when stimulated by a 40 Hz binaural beat, possibly leading to a more narrow focus. Hommel, Sellaro, Fischer, Borg & Colzato  found a cognitive bias toward flexibility when stimulated by a 40 Hz binaural beat, and Colzato, Steenbergen & Sellaro found that a binaural beat stimulation by 40 Hz affected the episodic memory . Of the two other studies, one failed to find any effects at all and the other found an effect as a result of beta binaural beat stimulation. López-Cabarello & Escera  tried to stimulate the students with binaural beats from the whole range, including the gamma range with beat frequencies of 4.53 Hz, 8.97 Hz, 17.93 Hz, 34.49 Hz and 57.3 Hz. They found no effects on measurements by EEG, ECG and SCR. Compared with the other studies in the review, this study utilized very short time for the binaural beats to work; only 3 minutes, and it may be considered if this can have affected the result. Beauchene, Abaid, Moran, Diana & Leonessa  found an increased response accuracy for working memory and brain acitivity reminiscent of high information transfer when stimulated by a 15 Hz beta binaural beats.
Four of the studies was done on different kind of patients with the goal of reducing disability. Two of the studies found indicators of reduced anxiety in patients scheduled for operation. Wiwatwongwana, Vichitvejpaisal, Thaikruea, Klaphajone, Tantong & Wiwatwongwana  found that an alpha beat stimulation at 10 Hz significantly reduced heart rate in patients undergoing cataract surgery under local anasthesia, indicating a reduction of operative anxiety by the use of alpha beat stimulation. Isik, Esen, Büyükerkmen, Kilinc & Menziletoglu  found that alpha beat stimulation at 9.3 Hz significantly reduced preoperative dental anxiety. Using the commercial theta beat stimulation "Dreamland" by Hemi-Sync, Gantt, Dadds, Burns, Glaser & Moore  found a significant reduction in cardiovascular stress as measured by Heart Rate Variability (HRV) in military service members with postdeployment stress. In a study on patients with Parkinson's Disease, Gálvez, Recuero, Canuet & Del-Pozo  found a significant decrease in theta-activity, general decrease in Functional Connectivity (FC) and improvements in working memory performances when the patients was stimulated by beta beat stimulation at 14 Hz.
The last study, done by Jirakittayakorn & Wongsawat , studied the effect of theta binaural beats on young adults. Utilizing a theta beat stimulation on 6 Hz, they found changes in theta activity on the entire cortex as measured by QEEG and decreased tension in the participants.
The table under summarize the effects found by the studies according to the beat frequencies, sample length in minutes and their range classification.
As already commented on, the variations of the study characteristics make it hard to come to a conclusion as to the potential effects of binaural beats. The rapid review done seems to strengthen the tendencies found by Chaieb, Wilpert, Reber & Fell  on the potential of binaural beats in reducing anxiety, and it also make a potential case for using binaural beats in learning situations.
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4. Reedijk, S. A., Bolders, A., Colzato, L. S. & Hommel, B. Eliminating the attentional blink through binaural beats: a case for tailored cognitive enhancement. Front Psychiatry 6, 82 (2015).
5. Colzato, L. S., Barone, H., Sellaro, R. & Hommel, B. More attentional focusing through binaural beats: evidence from the global–local task. Psychological Research 81, 271–277 (2017).
6. Hommel, B., Sellaro, R., Fischer, R., Borg, S. & Colzato, L. S. High-Frequency Binaural Beats Increase Cognitive Flexibility: Evidence from Dual-Task Crosstalk. Front. Psychol 7, 1287 (2016).
7. Colzato, L. S., Steenbergen, L. & Sellaro, R. The effect of gamma-enhancing binaural beats on the control of feature bindings. Exp Brain Res 235, 2125–2131 (2017).
8. López-Caballero, F. & Escera, C. Binaural Beat: A Failure to Enhance EEG Power and Emotional Arousal. Front. Hum. Neurosci. 11, 557 (2017).
9. Beauchene, C., Abaid, N., Moran, R., Diana, R. A. & Leonessa, A. The Effect of Binaural Beats on Visuospatial Working Memory and Cortical Connectivity. PLOS One 11, e0166630 (2016).
10. Wiwatwongwana, D. et al. The effect of music with and without binaural beat audio on operative anxiety in patients undergoing cataract surgery: a randomized controlled trial. Eye 30, 1407–1414 (2016).
11. Isik, B. K., Esen, A., Büyükerkmen, B., Kilinc, A. & Menziletoglu, D. Effectiveness of binaural beats in reducing preoperative dental anxiety. British Journal of Oral and Maxillofacial Surgery 55, 571–574 (2017).
12. Gantt, M. A., Dadds, S., Burns, D. S., Glaser, D. & Moore, A. D. The Effect of Binaural Beat Technology on the Cardiovascular Stress Response in Military Service Members With Postdeployment Stress. Journal of Nursing Scholarship 49, 411–420 (2017).
13. Gálvez, G., Recuero, M., Canuet, L. & Del-Pozo, F. Short-Term Effects of Binaural Beats on EEG Power, Functional Connectivity, Cognition, Gait and Anxiety in Parkinson’s Disease. Int J Neural Syst. 28, 1750055 (2018).
14. Jirakittayakorn, N. & Wongsawat, Y. Brain Responses to a 6-Hz Binaural Beat: Effects on General Theta Rhythm and Frontal Midline Theta Activity. Front. Neurosci. 11, 365 (2017).