You may have heard the term “brainwaves” used to describe brain activity. Brainwaves are a representation of the electrical activity of the brain produced by electroencephalography (EEG). In EEG, leads are attached to the scalp that amplify the electrical impulses of neurons as sensed at the surface. The EEG generates a wave pattern that represents the summed average wave lengths of tens to hundreds of thousands of neurons (depending on the number of leads attached and the length of time data are gathered). Over time, doctors have learned to associate certain brainwave frequencies with “states of mind”, that is to associate measured rates with cognitive states, including attention, drowsiness, dreaming, concentration, and relaxation, as examples. There is a range of what is considered “normal brainwave function”, because there is such a range of what is considered normal across the population. We call the brainwave present at rest in a person who is lying still with their eyes closed their background, also known as their posterior dominant rhythm (PDR). There is some disagreement on the fine details. However, generally speaking, when the PDR is approximately 8-12Hz, it is called alpha frequency range, and this range is considered a normal background in adults. Frequencies were named in the order of their discovery, rather than the order of their frequency range, so they are listed as follows:
Delta < 4Hz: Commonly seen in slow, non-REM sleep, has a role in declarative memory
Theta = 4 – 7.9Hz: Reported in meditative states, also seen in REM sleep, euphoric states
Alpha = 8 – 12.4Hz: Baseline relaxed state, also seen in REM sleep, attentive states
Beta = 12.5 – 24.9Hz: Baseline walking state, also seen under the influence of anti-anxiety drugs
Gamma > 25Hz: Bursts with site-specific utility

Many factors contribute to a person’s brainwave state. For example, cognitive control allows an otherwise relaxed person to “think” themselves into being anxious – through the active process of memory recall, the person recruits feelings that activate a stressful response. Or, if someone has an overactive amygdala, even at rest the person may be bombarded with feelings of fear or anger that prevent relaxation (LeDoux 2003). Sensory information from the body can also overwhelm the brain – pain is the simplest example of this. An easy way to change brain state is to simply close your eyes; many people will switch from beta (attentive) to alpha (relaxed) with just this exercise. Your brain is powerfully affected by what you see, and brainwaves can be overpowered with a visual signal as demonstrated in the figure to the right. An EEG recording of an awake person is shown. Normal resting pattern is on the left, and when a bright pulse of light is shown at 13Hz (Photic: pulses at the bottom), the subject’s brainwaves match the pulsing of the light. This process is known as entrainment, and the brainwave result is known as photic driving. Research showing the effect of sound on brainwave entrainment of EEG is more difficult to reproduce than studies in the visual system for photic driving. However, reliable scientific studies have shown the effect of binaural beats in alpha, beta, and gamma ranges using scalp electrodes (Vernon 2014, Pastor 2002, Schwarz 2005). Recordings were recently published using very high-fidelity electrodes in patients with implants deep inside the brain, undergoing evaluation for epilepsy surgery (Becher 2015). This data is particularly compelling because the number and clarity of electrode recording sites is far superior in surgical studies when compared to scalp recordings, which have significant interference that may prevent studies from finding an effect.

Studies in anxiety have been reproduced; an Australian hospital randomized patients in their emergency room to receive a 20-minute binaural beats track, an indistinguishable sham track, or calming white noises such as rainfall. The binaural beats track was shown to significantly reduce anxiety over both the sham track, and the white noise track (Weiland 2011). One of the more cited studies compared binaural beat exposures in beta and theta on a performance attention task for vigilance, and found that even though they had been blinded to the presence of a binaural beat exposure, people who were exposed to beta-frequency entrainment (16/24Hz) had significantly more correct target detections, and less negative mood compared to people who did the same tasks with white noise, or with theta/delta range frequencies (1.5/4Hz) (Lane 1998).

Any discussion of the few articles presented here, and of the many others available for review online and in the lay or academic press, must conclude that binaural beats represent a reproducible interface technology with potentially important effects on the human nervous system and behavior. It is also important to discuss the limitations of studies on this technology, and consider such limitations when describing how this technology will be used. First, there are general limitations regarding claims of EEG association with mood states – reporting of 140 141 both of these measures has a degree of subjectivity, in that mood is reported by survey and thus suffers immediately from recall and observation bias. So associating even a known EEG finding with mood to establish a baseline to test the binaural beat technology against is problematic. Likewise, EEG findings are not necessarily known for reliability – for example there is often considerable inter-rater reliability for clinical diagnoses (Benbadis 2009). Thus, results that find effects on comparatively more difficult states of attention or relaxation, often used as outcomes in neuropsychological studies, must be taken with some caution. In the case of studies discussed here, some care was taken to refer to work using generalizable metrics such as standardized surveys used in the FDA approval for anxiety medication (STA-I), or using randomized placebo controlled design.

Next, there are limitations to generalizing binaural beats across the range – just because the 9Hz binaural beat generator used for 20 minutes yielded a reproducible entrainment to alpha in study subjects, does not mean that the 9Hz binaural beat generator you have downloaded will produce the same result in you. Test conditions vary, as do tone used, volume, degree of noise cancellation and sensory isolation. Most importantly, the training used to prime expectations in study subjects can have a strong impact on outcomes. Any of these factors may modify the experience, and the extent to which they affect efficacy of brain entrainment is not known. For these reasons and others, an isolated and comfortable environment with limited distractions is an important component to creating a predictable binaural beat exposure process and results.

Finally, and perhaps most importantly, binaural beats suffer from many of the same limitations as other treatments that are not yet FDA-approved, namely lack of indications for their use, and lack of a dose-response curve for efficacy. Since these do not exist, caution should be taken while interpreting any claims made regarding a specific symptom that will be treated through a binaural beats exposure. However, a sufficient amount of evidence appears to justify the claim that binaural beat exposures of approximately 20 minutes can be effective at assisting transition to states of reduced anxiety and increased attention, and may even have utility for reducing the perception of pain – it would be useful to see studies that reproduced the findings cited here. There are other, less well described but significant areas of exciting research ongoing for use of binaural beats to assist in reducing insomnia, for improving performance in cognitive behavioral therapy sessions when used as an adjuvant to traditional psychotherapy.