Binaural beats are an auditory illusion that occurs when two tones of slightly different frequencies are played in each ear.
Some claim that binaural beats can synchronize and entrain brainwaves to match the difference frequency.
But does scientific evidence support these alleged “brainwave entrainment” effects?
A new systematic review published in PLOS ONE analyzed the available research on whether binaural beats can truly entrain brainwaves as claimed.
Key Facts:
- Binaural beats are an auditory illusion that occurs when two tones of slightly different frequencies are presented to each ear.
- Some claim binaural beats can “entrain” brainwaves to oscillate at the difference frequency, known as the “brainwave entrainment” hypothesis.
- A new systematic review analyzed 14 EEG studies on binaural beats to evaluate the evidence for brainwave entrainment effects.
- 5 studies supported the brainwave entrainment hypothesis, 8 studies found no effects, and 1 had mixed results.
- The review concluded the evidence is currently inconclusive due to substantial heterogeneity in research methods.
- More standardized research is needed to determine if binaural beats can reliably entrain brainwaves as claimed.
Source: PLOS One 2023
What are Binaural Beats?
Binaural beats are an auditory illusion that occurs when two tones of slightly different frequencies are presented separately to each ear using stereo headphones.
For example, if a 400 Hz tone is played in the right ear, and a 410 Hz tone is played simultaneously in the left ear, most people will perceive a subjective “beating” tone that pulses at 10 Hz.
This 10 Hz tone is known as the binaural beat.
The binaural beating percept arises from brain processing in the superior olivary nucleus, the first structure where inputs from both ears converge.
Neurons in this area are sensitive to small timing and phase differences between sounds at the two ears.
They use these timing differences to help locate sounds in 3D space.
With binaural beats, the two tones stimulate different timing and phase information that the brain interprets as a 10 Hz oscillation, even though no 10 Hz tone is physically present in the stimulus.
Binaural Beats and “Brainwave Entrainment”
Some proponents claim binaural beats can “entrain” brainwaves, synchronizing EEG rhythms in the brain to match the frequency of the binaural beat.
Through this purported “brainwave entrainment” effect, binaural beats are claimed to alter cognition, mood, physiology, and more based on the stimulated EEG band.
For example, boosting alpha waves (8-12 Hz) could increase relaxation, while increasing beta waves (13-30 Hz) could improve concentration and cognition.
This brainwave entrainment hypothesis is based on the fact that neural activity in the brain generates oscillating electrical signals detectable by EEG.
Certain EEG frequency bands like alpha and beta have been linked to different mental states.
If binaural beats can entrain EEG rhythms to consistently match the frequency of the beat, in theory they could modulate brainwaves and associated mental states.
However, previous reviews suggest many studies fail to find clear EEG evidence of brainwave entrainment from binaural beats.
The authors of this new review aimed to systematically collect and analyze all existing research on whether binaural beats produce brainwave entrainment effects to evaluate the current evidence.
A Systematic Review of Binaural Beats Effects on Brain Waves
The authors conducted a systematic search of scientific databases to identify all published studies that tested binaural beat stimulation effects on human EEG signals.
To be included, studies had to use binaural beats within the range of normal brain rhythms (<30 Hz), present them in isolation without additional stimuli, include a control condition not expected to produce entrainment, and measure EEG to test for entrainment effects.
14 studies published between 2007-2023 met the strict inclusion criteria (out of 185 initially identified).
The selected studies were analyzed and rated for their methodological quality using standard scientific criteria.
Key details were extracted from each study, including experimental methods, EEG analysis techniques, results, and conclusions about brainwave entrainment effects.
Review of Study Methods and Quality
The review found research methods and study quality varied widely across the 14 included studies:
- Sample sizes ranged from just 4 to 47 participants, mostly young healthy adults.
- Binaural beat frequencies ranged from 1 Hz to 40 Hz, covering delta to gamma EEG bands.
- Duration of binaural beat stimulation ranged from 1 minute to 30 minutes.
- 10 studies used isolated binaural beats, while 4 embedded beats in pink noise.
- Only 6 studies included proper control groups for comparison, while 10 used within-subject designs.
- Analysis techniques for assessing “entrainment” differed, from simple EEG power to phase locking and connectivity measures.
- Most studies analyzed short-term EEG changes and lacked longer pre/post monitoring.
The authors noted substantial heterogeneity in research methods, with lack of standardization across most aspects of study protocols.
They concluded this severely limits comparability between the studies and their ability to provide definitive evidence for or against brainwave entrainment effects.
However, some consistent trends did emerge in the results.
Review of Binaural Beats Study Outcomes and Conclusions
The review categorized studies as either supporting brainwave entrainment from binaural beats (5 studies), not supporting it (8 studies), or having mixed results (1 study):
Supporting Brainwave Entrainment (5 studies):
- Increased theta power after 6-10 minutes of theta beats
- Increased alpha power after 5 minutes of alpha beats
- Increased gamma power after 15 minutes of gamma beats
- Alpha boosting from delta beats (cross-frequency effect)
- Changes in theta connectivity measures
Not Supporting Brainwave Entrainment (8 studies):
- No change in EEG power in any band, including theta, alpha, beta, gamma
- No difference from monaural beats
- Greater theta increase for control pink noise than binaural beats
- General EEG power increase but no specific frequency changes
Mixed Results (1 study):
- Theta connectivity changes but no theta power change from theta beats
In summary, 8 studies found no changes in EEG power consistent with brainwave entrainment.
However, 5 studies did report some indications of entrainment, mostly in the theta band.
The single study with mixed results highlights that analysis method also impacts outcomes.
Due to the substantial methodological heterogeneity, the conflicting results could not be formally pooled in a meta-analysis.
However, the authors concluded the evidence remains inconclusive regarding brainwave entrainment from binaural beats.
The diversity of protocols may account for some conflicting results.
More rigorously standardized research is needed to resolve the debate.
They also noted that many applied studies claiming psychological effects from “brainwave entrainment” lack proper EEG measures to confirm entrainment occurred.
This review casts doubt on conclusions from such studies.
Future Directions for Brainwave Entrainment Research
Based on this systematic review, the authors provided recommendations for improving future EEG research on binaural beat brainwave entrainment:
- Use well-controlled study designs, including comparison groups and multiple pre/post assessments
- Test wider age groups beyond just young adults
- Standardize protocols, including frequencies, durations, and noise conditions
- Reach consensus on definitions and EEG measures of entrainment
- Assess both spectral power and temporal dynamics like ASSR
- Require applied studies demonstrate entrainment before inferring causal effects
They concluded that more rigorous, standardized protocols are imperative to reach scientific consensus on if and how binaural beats may entrain brainwaves.
This review highlights the need and establishes a roadmap for better research into this popular auditory phenomenon.
References
- Study: Binaural beats to entrain the brain? A systematic review of the effects of binaural beat stimulation on brain oscillatory activity and the implications for psychological research and intervention
- Authors: Ruth Maria Ingendoh et al. (2023)
