What are binaural beats

When two coherent sounds with nearly similar frequencies and with stable amplitudes are presented to each ear respectively with stereo headphones, the brain integrates the two signals and produces a sensation of a third sound called binaural beat, which appears subjectively to be located “inside” the head. Binaural beat technology products are sold internationally as personal development and health improvement tools. Manufacturers suggest benefit from regular listening to binaural beats including reduced stress and anxiety, and increased focus, concentration, motivation, confidence, and depth in meditation.

Binaural beats utilize a phenomenon that occurs within the cerebral cortex when two different frequencies are presented separately to each ear. This procedure produces a third phantom binaural beat, whose frequency is equal to the difference of the two presented tones and which can be manipulated for non-invasive brain stimulation ¹⁾. The binaural beat percept was first reported by H. W. Dove in 1839 and outlined in detail by Oster over five decades ago ²⁾. Oster reported that the binaural beats were detected only when the carrier frequency was below 1000 Hz, a finding that confirmed an earlier study by Licklider and colleagues ³⁾. This indicates that beat carrier frequencies have to be sufficiently low enough to be temporally encoded by the cortex ⁴⁾. For instance, when a tone of 335 Hz is presented to the right ear and a tone of 345 Hz to the left ear, this results in a subjectively perceived binaural beat of 10 Hz. Hence, instead of hearing two different tones, most individuals will hear just one tone that fluctuates in frequency or loudness: a beat ⁵⁾. How exactly the brain produces the perception of these beats is unclear, but the reticular activation system and the inferior colliculus seem to play a role ⁶⁾. In animals, binaural-beat producing stimulus conditions have been shown to produce particular neural patterns of phase locking or synchronization, beginning in the auditory system and propagating to the inferior colliculus ⁷⁾. Even though the neural response to objectively presented beats is stronger, binaural beats seem to elicit similar neural responses in both humans and animals ⁸⁾, suggesting that the illusion arises through pathways normally associated with binaural sound detection ⁹⁾. As in humans binaural beats have been found to affect cognitive functioning and mood ¹⁰⁾, and responses to binaural beats are detectable in the human electroencephalography (EEG) ¹¹⁾, it can be assumed that neuronal phase locking spreads from the auditory system and the inferior colliculus over the cortex. A spreading pattern of neuronal activation and synchronization might affect short- and long-distance communication in the brain, processes which depend on neuronal synchronization and, presumably, on particular neurotransmitter systems ¹²⁾, thus affecting cognitive processing.

Binaural beat is believed to offer a non-invasive method for manipulating cortical synchronization. Binaural beats take advantage of the brain’s response to two pure tones, delivered independently to each ear, when those tones have a small frequency mismatch. The mismatch between the tones is interpreted as a beat frequency, which may act to synchronize cortical oscillations ¹³⁾. Neural synchrony is particularly important for working memory processes, the system controlling online organization and retention of information for successful goal-directed behavior ¹⁴⁾. Therefore, manipulation of synchrony via binaural beats provides a unique window into working memory and associated connectivity of cortical networks ¹⁵⁾. Although earlier studies showed that binaural beats could influence behavior and cognition, common agreement on the mechanism of binaural beats has not been reached yet.

Binaural beats requires the presentation of two different tones to the ears ¹⁶⁾. This procedure causes a third phantom binaural beat, whose frequency is equal to the difference of the two presented tones, to be produced within the Inferior Colliculus located in the auditory pathway ¹⁷⁾. The overall phase difference is preserved from the inferior colliculus to the auditory cortex by periodic neural firing at the binaural beat frequency ¹⁸⁾.

If binaural beats affect cognition through neural synchronization, it is possible that the frequency of the beat matters. For instance, short-range communication within brain areas is often associated with neural synchronization in the gamma frequency, while long-range communication is associated with neuronal phase locking in the slower frequency bands ¹⁹⁾. Moreover, a variety of frequency bands have been considered to represent the “messenger frequency” of cognitive-control signals. For instance, synchronization in the gamma frequency range seems to play a role in the top-down control of memory retrieval ²⁰⁾, which should be relevant for many creativity tasks. Also of interest, phase locking in the alpha band has been associated with lower cortical arousal in general ²¹⁾ and enhanced top-down control in creativity-related performance in particular ²²⁾. Especially divergent thinking seems to be associated with alpha wave synchronization ²³⁾. It could therefore be reasoned that inducing a state of lower cortical arousal by presenting people with alpha frequency binaural beats temporarily increases their performance on a divergent thinking task. The highest amount of synchronization in the auditory cortex due to binaural beats occurs within the beta band at 16Hz ²⁴⁾.

Figure 1. Binaural beats example (255 Hz – 240 Hz = 15Hz Binaural Beat)

Previous work has demonstrated that binaural beats can affect cortical responses across frequency bands. Within the gamma band, the largest electroencephalography (EEG) steady state responses occurred with a binaural beat of 40Hz and primarily activated the frontal and parietal lobes ²⁵⁾. In addition, binaural beat stimulation in the beta band at 18.5Hz increased electroencephalography (EEG) magnitude by 21% ²⁶⁾. Areas of the cortex entrained by theta band binaural beats include parietal, frontal, and temporal areas ²⁷⁾. However, binaural beats can influence activity outside their respective frequency band and this effect is not well characterized. For example, Gao et al. ²⁸⁾ reported that, during either delta or alpha binaural beat stimulation, the EEG power increased in their respective band. However, in addition to the stimulated band, the relative EEG power increased in the theta and alpha bands as well.

A previous study, by Ioannou et al. ²⁹⁾, investigated the impact of binaural beats on phase synchrony measures in both musicians and non-musicians. They found that binaural beat stimulation in the alpha band created the highest steady state responses in both groups. In addition, they determined that listening to low frequency binaural beats had a significant impact on the structure of the cortical connectivity network in the alpha band ³⁰⁾. This work suggests that binaural beats will be able to significantly impact the network topology for improving memory ³¹⁾.

Although binaural beats offer a noninvasive and easily administered stimulus, their effect on working memory has been explored in only a small number of studies. Kennerly ³²⁾ investigated the effect of binaural beats on performance during memory span tasks. The author concluded that the binaural beat groups performed significantly better when compared to the control group. Fernandez et al. ³³⁾ tested the effects of binaural beats on verbal working memory. Participants performed significantly better on a word recall task when listening to 5Hz binaural beat when compared to 13Hz. Lane et al. ³⁴⁾ tested participant performance during a 1-back working memory test while listening to either theta or beta range binaural beats. While listening to binaural beats in the beta frequency range, participants showed improvement in target detection, and decreased false alarms, task-related confusion, and fatigue. Although previous studies suggest that binaural beats offer noninvasive manipulation of brain activity that produces behavioral changes in working memory performance, prior studies have not investigated the neural mechanisms that drive the behavioral changes.

Neurophysiology of auditory beat processing

Acoustic stimuli are heard when the peripheral components of the auditory pathway (ears, cochlea, and inner hair cells) convert pressure waves into neural action potentials via mechano-electrical transduction. This is the first order of auditory processing prior to sound waves being encoded (or rather re-encoded) by the primary auditory cortex. Auditory information is further processed at a number of subcortical structures. Auditory nerve fibers leaving the cochlea converge with the vestibulocochlear nerve and enter the cochlear nucleus in the brainstem and bifurcate. As the nerve fibers branch they form synapses with different subtypes of neurons – spherical bushy cells, globular bushy cells, and stellate cells, each of which differ in their temporal and spectral response properties ³⁵⁾. Information is then relayed to either the inferior colliculus via outputs from the stellate and dorsal cochlear nucleus cells, or by an indirect route to the superior olivary complex. Bushy cells of the anteroventral cochlear nucleus project outputs via this route ³⁶⁾. The superior olivary complex processes convergent information from the left and right ears and cues related to sound localization ³⁷⁾. The left and right inferior colliculus has a commissural connection, which allows for binaural interactions within the ascending pathway, and is comprised of numerous subnuclei, the largest of which is the central nucleus ³⁸⁾. Here, the temporal integration window between the inferior colliculus and the auditory cortex enables processing of monaural characteristics such as amplitude modulation ³⁹⁾. From here, outputs travel to the medial geniculate nucleus of the thalamus, where thalamic output fibers connect to the auditory cortex located in the temporal lobes ⁴⁰⁾.

The neurophysiological processing of binaural and monaural beats differs slightly. Draganova and colleagues underlined these differences by referring to monaural beats as “peripheral” – as they interacted at the cochlear level, and binaural beats as “central,” i.e., the binaural beat percept being the result of the effect of a central interaction which mostly likely occurs in the superior olivary nuclei ⁴¹⁾. Monaural beats are heard when a composite auditory stimulus is presented to both ears simultaneously, which is detected by the cochlear and relayed to the brain stem and auditory cortex. Binaural beats, however, are only subjectively perceived when two sine waves of nearby frequencies are delivered to each ear separately. Brainstem neurons in the superior olivary complex, which are sensitive to phase shifts between both ears, fire action potentials at a rate corresponding to the phase difference between both ears and generate the binaural-beat percept. Thus the binaural-beat percept is caused by the major neural mechanism which enables sound localization ⁴²⁾.

The auditory steady-state response is a composite auditory evoked potential which can be elicited using repetitive acoustic stimuli which continually persist over a time period. The auditory steady-state response follows the envelope of a complex stimulus, and it has been suggested that the steady-state response drives the background activity of the EEG ⁴³⁾. Regan defines the steady-state response as “an evoked potential whose constituent discrete frequency components remain constant in amplitude and phase over an extended time period” ⁴⁴⁾.

To probe the cortical representation of binaural-beat frequencies, Karino et al. ⁴⁵⁾ applied modulation frequencies of 4.00–6.66 Hz while recording magnetic fields using magnetoencephalography. The authors reported that the binaural beat auditory steady-state response arose from the superior temporal, posterior parietal, and frontal cortices, in addition to the auditory cortex. Another study applied a similar technique to that of Pantev et al. ⁴⁶⁾, by comparing a transient of the MLR–N1m to auditory steady-state response responses to monaural and binaural-beat stimuli, recorded using magnetoencephalography ⁴⁷⁾. Their findings showed that auditory steady-state response to both monaural- and binaural-beat stimuli are located anterior and medially to Heschl’s gyri within the Sylvian fissure, and when compared with the N1m source, place the auditory steady-state response generating network within the primary auditory cortex, which is also in line with other studies ⁴⁸⁾. The authors also observed that the magnetic field amplitudes of the auditory steady-state response elicited by monaural beats were ~5 greater than those of the auditory steady-state response to binaural beats ⁴⁹⁾. A recent study has also reported similar findings concerning the magnitude of responses to monaural and binaural beats, and that stimulation conditions were reflected in interhemispheric phase differences ⁵⁰⁾. Schwartz and Taylor ⁵¹⁾ also reported a lesser auditory steady-state response amplitude response to binaural-beat stimuli compared to monaural beats. A 40 Hz binaural beat auditory steady-state response was evoked with a carrier frequency at 400 Hz but was undetectable above 3000 Hz. This was not the case for the monaural beat stimulation frequencies, which could be detected above 3000 Hz.

Do binaural beats actually work?

The brain responses to binaural beats remain controversial. Many investigations of brain responses to binaural beat stimuli have been conducted; however, the results are controversial and continue to be debated ⁵²⁾. Several factors including beat frequency, carrier tone frequency, exposure duration, and recording procedures interfere with the discussion process, as these factors affect brain responses, and differences in these factors do not allow for clear comparisons among studies.

Some scientists are determined that listening to 15 Hz binaural beats during an N-Back working memory task increased the individual participant’s accuracy, modulated the cortical frequency response, and changed the cortical network connection strengths during the task. According to Beauchene and colleagues ⁵³⁾ only the 15 Hz binaural beats produced significant change in relative accuracy compared to the None condition. Listening to 15 Hz binaural beats during the N-back task activated salient frequency bands and produced networks characterized by higher information transfer as compared to other auditory stimulation conditions ⁵⁴⁾.
Listening to 15Hz binaural beats positively influenced the participants’ accuracy during the course of the 5 minutes by 3%. During all other conditions, the participants’ accuracy decreased by 1%—3%. No Sound and 5Hz binaural beats produced a smaller decrease in accuracy while the Pure Tone, Classical Music, and 10Hz binaural beats produced the largest decreases ⁵⁵⁾. This increase in performance of the working memory task can be explained by noting that 15Hz binaural beats produces high synchronization within the auditory cortex ⁵⁶⁾ and falls within the beta band which is often associated with active concentration.

Although listening to 15Hz binaural beats during a visuospatial working memory task may increase the response accuracy and also change the properties of the the cortical networks supporting task performance ⁵⁷⁾. Other study ⁵⁸⁾ found that binaural beats do not represent a one-size-fits-all enhancement technique. Binaural beats can be effective in enhancing brainstorm-like creative thinking in individuals with low striatal dopamine levels, but they can at the same time impair performance in exactly the same kind of task in others ⁵⁹⁾. This calls for more care in the propagation of binaural beats as a cognitive-enhancement method and a better understanding of the underlying neural and cognitive mechanisms.

Studies have found no evidence for any influence of binaural beats on convergent thinking, while divergent thinking was systematically affected depending on base-line spontaneous eye blink rate. This supports the assumption that convergent thinking, and other kinds of highly constrained top-down search processes, rely more on the frontal part of the frontal-striatal interaction constituting cognitive control ⁶⁰⁾, while divergent thinking, and other forms of mental flexibility, lean more towards the striatal part ⁶¹⁾. Moreover, the observation of a differential effect on one of the two kinds of creative performance reinforces claims that human creativity is not a unitary function but consists of multiple components ⁶²⁾.

Studies could not find any difference between the Alpha and the Gamma condition—both had the same kind and the same degree of impact on divergent thinking. This suggests that binaural beats do not so much trigger or facilitate a particular neural synchronization processes but rather support neuronal phase locking in general ⁶³⁾. For instance, they might impose some temporal structure on neural processes and thereby reduce cortical noise ⁶⁴⁾, which again may make task-specific processes that rely on neural communication and/or synchronization more reliable. In which frequency this temporal structure is operating might be less relevant.

A study by Reedijk et al. ⁶⁵⁾ found that binaural beats do not represent a suitable all-round tool for cognitive enhancement. While participants with lower spontaneous eye blink rates (20 blinks per min or lower) showed clear beat-induced benefits in divergent thinking, binaural beats impaired the performance of individuals with higher spontaneous eye blink rates (20 blinks per min or higher. As suspected, this suggests that beat-induced cognitive enhancement depends on the individual striatal dopamine level—an observation that parallels Akbari Chermahini and Hommel’s ⁶⁶⁾ finding of equally selective mood effects on divergent thinking.

There are at least two possible, not mutually exclusive explanations for this observation. First, there is evidence that lower-than-average eye blink rate levels are associated with less effective performance in divergent-thinking tasks, especially regarding flexibility ⁶⁷⁾. Even though this difference just missed the significance criterion, individuals with rather low striatal dopamine levels might have more room for improvement and are, thus, more sensitive to cognitive-enhancement procedures. For instance, it might be that binaural beats induce, or increase the size of phasic dopamine bursts, which might have a stronger impact in individuals with a relatively low tonic dopamine level. Individuals with a more suitable dopamine level may not need these extra or extra-sized bursts and may end up with more than optimal cortical noise. This would also suggest that eye blink rates mainly reflect tonic dopamine activity in the striatum, but this lies outside the scope of the current study and, thus, remains speculation for now.

Second, it might be that binaural beats do not operate directly on the individual dopamine level, be it tonic or phasic. Note that Reedijk et al. ⁶⁸⁾ did not find any systematic, beat-induced mood effects. To the degree that changes in dopamine levels are accompanied by changes in mood ⁶⁹⁾, this might suggest that binaural beats facilitated or enabled processes that compensate for the individual lack of striatal dopamine. For instance, it might be that dopamine is functional in driving neural synchronization ⁷⁰⁾. If so, a relatively low level of striatal dopamine may thus make it more difficult to set up synchronized neural states, and this difficulty may somehow be overcome through other, compensatory processes that are induced or facilitated by binaural beats. As speculated earlier, binaural beats may increase the temporal structure of idling neural activities and thereby reduce cortical noise, which again might facilitate setting up synchronized states. Again, it is conceivable that individuals with more optimal dopamine levels do not need, or may even be impaired by this alternative way to create the necessary synchronized states.

Irrespective of which of these two scenarios will turn out to be more realistic, it is clear that binaural beats do not represent a one-size-fits-all enhancement technique. They can be effective in enhancing brainstorm-like creative thinking in individuals with low striatal dopamine levels, but they can at the same time impair performance in exactly the same kind of task in others. On the one hand, this calls for more care in the propagation of binaural beats as a cognitive-enhancement method and a better understanding of the underlying neural and cognitive mechanisms. On the other hand, however, it also implies that previous failures to find positive effects of binaural beats on cognitive performance need not be taken as evidence against the efficiency of the manipulation. In fact, careful selection of individuals involving a systematic evaluation of their cognitive control profiles is likely to yield evidence of cognitive enhancement, even under conditions that proved ineffective by previous research.

While findings for most putative applications up to now are either solitary or contradictory, several studies consistently report a diminishing impact of binaural beats stimulation on anxiety levels. The underlying neural mechanisms are still yet to be unraveled. Understanding how and where the binaural-beat percept is generated and which cortical networks are most affected will aid in the optimization of both monaural and binaural-beat stimulation as a tool to modulate cognitive and mode states. Many studies employing auditory beat stimulation as either a mechanistic tool or potential therapeutic aid, report contrasting findings. Further research, including more accurate reporting of experimental protocols, especially those studies undertaken in a clinical setting, will help to clarify the most promising effects. In a recent study, Ross and colleagues ⁷¹⁾ reported that inconsistencies relating to monaural and binaural beats at low frequencies, as well as at the 40 Hz frequency, could possibly be attributed to earlier investigations suggesting that they share common neural mechanisms. Many factors may impact upon the efficacy of beat stimulation, including the duration of the applied stimulus. Carrier frequencies may also play a role, as well as the addition of background white or pink noise, which may amplify the beat percept ⁷²⁾.

A study examining the effects of aging showed that regardless of age, a binaural-beat percept in the gamma range could be detected, but with less accuracy by older individuals ⁷³⁾. Some investigations also reported gender differences concerning binaural-beat perception ⁷⁴⁾ and alterations in auditory perception during the menstrual cycle ⁷⁵⁾. Other studies suggest that attending to the stimulus may play role ⁷⁶⁾. As many factors impact upon the efficacy of monaural and binaural-beat stimulation, a more in-depth reporting of beat stimulation parameters and protocols would offer the possibility to limit the methodological inconsistencies that may explain many of the contradictory outcomes reported in the literature. Most importantly, electrophysiological investigations comparing the effects of auditory beats under different stimulation conditions and parameters are still rare. Such studies are necessary as a fundament to allow the development of mechanistic hypotheses explaining the behavioral outcomes of beat stimulation.

Figure 3. Human brain

Figure 4. Cerebrum of the brain

Binaural beats and anxiety

A volunteer sample of 15 mildly anxious patients were asked to listen at least 5 times weekly for 4 weeks to 1 or more of 3 music tapes containing tones that produce binaural beats in the electroencephalogram delta/theta frequency range ⁷⁷⁾. Participants also were asked to record tape usage, tape preference, and anxiety ratings in a journal before and after listening to the tape or tapes. Anxiety ratings before and after tape listening, pre- and post-study State-Trait Anxiety Inventory scores, and tape preferences documented in daily journals. Listening to the binaural beat tapes resulted in a significant reduction in the anxiety score reported daily in patients’ diaries. The number of times participants listened to the tapes in 4 weeks ranged from 10 to 17 (an average of 1.4 to 2.4 times per week) for approximately 30 minutes per session. End-of-study tape preferences indicated that slightly more participants preferred tape B, with its pronounced and extended patterns of binaural beats, over tapes A and C. Changes in pre- and posttest listening State-Trait Anxiety Inventory scores trended toward a reduction of anxiety, but these differences were not statistically significant ⁷⁸⁾.

Binaural beats and preoperative dental anxiety

Sixty patients (30 in each group) who were to have impacted third molars removed were studied (experimental group: 20 women and 10 men, mean (range) age 24 (18‐35) years, and control group: 22 women and 8 men, mean (range) age 28 (15‐47) years) ⁷⁹⁾. All patients were fully informed about the operation preoperatively, and their anxiety recorded on a visual analogue scale (VAS). The local anaesthetic was given and the patients waited for 10minutes, during which those in the experimental group were asked to listen to binaural beats through stereo earphones (200Hz for the left ear and 209.3Hz for the right ear). No special treatment was given to the control group. In both groups anxiety was then recorded again, and the tooth removed in the usual way. The degree of anxiety in the control group was unchanged after the second measurement, while that in the experimental group showed a significant reduction in anxiety. The study authors concluded that binaural beats may be useful in reducing preoperative anxiety in dentistry ⁸⁰⁾.

Binaural beats and sleep

The effect of sleep deprivation on psychophysical performance and well-being is comprehensively investigated. This study ⁸¹⁾ aims to investigate whether sleep quality of top athletes can be improved by auditory brainwave entrainment and whether this leads to enhancements of post-sleep psychophysical states. In a pilot study, 15 young elite soccer players were stimulated for eight weeks during sleep with binaural beats around 2-8 Hz. Once a week after wake-up, participants completed three different questionnaires: a sleep diary, an adjective list for psychophysical and motivational state, and a self-assessment questionnaire for sleep and awakening quality. Fifteen sport students executed the same protocol sleeping on the same pillow, but without stimulation. Subjective ratings of sleep and awakening quality, sleepiness and motivational state were significantly improved only in the intervention group, but did not impact their perceived physical state ⁸²⁾. In summary, eight weeks of auditory stimulation with binaural beats improved perceived sleep quality and the post-sleep state of athletes, whereas the effect on physical level is assumed to occur in a time-delayed fashion ⁸³⁾.

Binaural beats and focus

Little evidence exists that binaural beat entrainment can alter attention and behavioral performance ⁸⁴⁾. The anecdotal reports and few experimental studies that do exist tend to reach conflicting conclusions. Noh et al. ⁸⁵⁾ conducted a randomized controlled study with two different types of binaural beats to investigate their effects on attention. Eight participants were exposed to different binaural beat protocols (beta and theta) on 2 separate days. Pairing entrainment sessions allowed participants to act as their own control for possible entrainment effects. A 64‐channel EEG was recorded before, during, and after the presentation of binaural beats. The Lateralized Network Attention Test was also administered during the presentation of binaural beats, to measure changes in covert orienting of spatial attention in each hemisphere. The authors found significantly different effects of the 2 binaural beat types on conflict resolution and spatial orienting in the 2 hemispheres. EEG analysis is expected to reveal differences in individual subject spectral measures before and after entrainment sessions ⁸⁶⁾.

Binaural beats and chronic pain

The pilot study ⁸⁷⁾ assessed the effects that an external, audio, neural stimulus of theta binaural beats had on returning the brain neurosignature for chronic pain to homeostasis. Thirty-six US adults with various types of chronic pain, and with a median age of 47 years, ranging in ages from 26-69 years, participated in the study. The study experienced 4 dropouts. Participants listened to 2 recordings-one using theta binaural beats at 6 Hz (theta binaural beats intervention) and one using a placebo of a nonbinaural beat tone of 300 Hz (sham intervention) for 20 min daily. Both interventions lasted 14 successive days each, with some participants hearing the theta binaural beats intervention first and the sham intervention second and some hearing them in the reverse order. Participants listened to the interventions via a website on the Internet or via a compact disc. Interviews were conducted either in person or telephonically with e-mail support. Although the theta binaural beats and the placebo interventions both reduced the pain scores, analysis indicated a large main effect for the theta binaural beats intervention in reducing perceived pain severity. The results supported the hypothesis that an external audio protocol of theta binaural beats was effective in reducing perceived pain severity for participants ⁸⁸⁾.

Binaural beats and meditation

During meditation, theta activity of the meditative state presents as a general theta rhythm and frontal midline theta activity ⁸⁹⁾. In general theta rhythm, the power of theta activity is higher than normal at the frontal and parietal-central regions but does not appear at posterior regions. In frontal midline theta activity (FmTheta), the power of theta activity is higher at the frontal midline cortical position, specifically at the Fz position, and without this activity, a meditative state is not achieved. The finding of this study ⁹⁰⁾ appears to indicate that the 6-Hz binaural beat could be utilized to induce a meditative state within a short duration. The carrier tone of 250 Hz was presented to the left ear, and the offset tone of 256 Hz was presented to the right ear and the volume was set at 65 dB. The results showed that theta activity was induced in the entire cortex within 10 min of exposure to the stimulus in the experimental group and compared to the control group, the induced responses at the frontal and parietal-central regions were left hemisphere dominant. Moreover, the pattern of theta activity was similar to that of a meditative state, in which general theta rhythms were increased at the frontal and parietal-central regions and frontal midline theta activity appeared at the Fz position within 10 min stimulus exposure. Therefore, the authors ⁹¹⁾ suggested that a 6-Hz binaural beat on a 250 Hz carrier tone could be used as a stimulus for inducing a meditative state within a short duration.

A study was conducted to determine the quantitative electroencephalographic correlates of meditation, as well as the effects of hindering (15 Hz) and facilitative (7 Hz) binaural beats on the meditative process ⁹²⁾. The subjects comprised novice (mean of 8 months experience) and experienced (mean of 18 years experience) meditators recruited from local meditation groups. Experimental manipulation included application of hindering and facilitative binaural beats to the meditative process. Experienced meditators displayed increased left temporal lobe delta power when the facilitative binaural beats were applied, whereas the effect was not observed for the novice subjects in this condition. When the hindering binaural beats were introduced, the novice subjects consistently displayed more gamma power than the experienced subjects over the course of their meditation, relative to baseline. Based on the results of this study, novice meditators were not able to maintain certain levels of theta power (theta activity is common during meditation) in the occipital regions when hindering binaural beats were presented, whereas when the facilitative binaural beats were presented, the experienced meditators displayed increased theta power in the left temporal lobe. These results suggest that the experienced meditators have developed techniques over the course of their meditation practice to counter hindering environmental stimuli, whereas the novice meditators have not yet developed those techniques ⁹³⁾.