The story of brainwave entrainment research spans nearly a century, beginning with a German psychiatrist's persistent efforts to record the electrical activity of the human brain. What started as a controversial claim in 1929 has evolved into a sophisticated field encompassing neuroscience, audiology, and cognitive research, with applications ranging from clinical therapy to consumer wellness products.
This historical overview traces the key discoveries, researchers, and technological developments that shaped our understanding of how external stimuli can influence brain rhythms. From the earliest electroencephalography (EEG) recordings to modern investigations using 40Hz light and sound, each advancement built upon previous work to create the foundation for contemporary entrainment research.
What Is Brainwave Entrainment?
Brainwave entrainment refers to the observation that brain electrical activity can synchronize with external rhythmic stimuli. Researchers have investigated this phenomenon using:
- Photic (light-based) stimulation at specific frequencies
- Auditory stimulation including binaural and monaural beats
- Transcranial electrical stimulation methods
- Combined audiovisual approaches
The extent and practical significance of entrainment effects remain subjects of ongoing scientific investigation.
1929: Hans Berger Discovers Alpha Waves
The history of brainwave entrainment begins with the history of EEG itself. Hans Berger (1873-1941), a German psychiatrist at the University of Jena, spent years attempting to measure the electrical activity of the human brain. His interest in psychic phenomena and telepathy initially motivated this work, as he believed electrical brain activity might explain such experiences.
In 1924, Berger succeeded in recording the first human EEG using silver foil electrodes placed on the scalp of a patient with a skull defect from a previous surgery. However, he did not publish his findings until 1929, having spent five years refining his technique and gathering additional evidence.1
Historical Note: Berger coined the term "electroencephalogram" and identified two distinct types of brain waves. He named the larger, slower oscillations "alpha waves" (occurring at approximately 8-12 Hz when subjects were relaxed with eyes closed) and the smaller, faster oscillations "beta waves" (occurring during active mental concentration).2
Initial Skepticism and Reception
Berger's 1929 paper, "On the Electroencephalogram of Man," was met with significant skepticism from the scientific community. Many researchers doubted that electrical signals from the brain could be detected through the skull and scalp. The idea that the brain produced measurable rhythmic electrical activity seemed implausible to many contemporaries.
Berger continued publishing papers throughout the early 1930s, documenting his observations systematically. He noted that alpha waves appeared most prominently when subjects were awake but relaxed with their eyes closed, and that opening the eyes or engaging in mental arithmetic would cause the alpha rhythm to be replaced by faster, lower-amplitude beta activity. This observation, later called "alpha blocking" or the "Berger effect," became one of the first documented examples of how external conditions could modulate brain electrical activity.3
The Berger Effect
Berger observed that when subjects opened their eyes or engaged in mental tasks, their alpha waves would diminish or disappear, replaced by faster beta activity. When they closed their eyes and relaxed again, alpha rhythms would return. This demonstrated that brain electrical activity responded to behavioral and cognitive states, laying groundwork for later investigations into whether external stimuli could influence these rhythms.
Berger's meticulous documentation included over 1,400 individual EEG recordings. Despite the initial resistance to his work, his persistence in gathering evidence eventually led to wider acceptance of electroencephalography as a legitimate scientific tool.
1934: Adrian and Matthews Confirm EEG
The turning point for EEG acceptance came in 1934 when two prominent British physiologists, Edgar Douglas Adrian and Bryan Matthews at Cambridge University, independently replicated and confirmed Berger's findings. Adrian was already a Nobel laureate (1932) for his work on nerve impulse transmission, lending significant credibility to the validation.4
Adrian and Matthews used improved amplification equipment and confirmed that the rhythmic electrical signals Berger had reported were indeed originating from the brain, not from muscle artifacts or equipment noise as skeptics had suggested. Their confirmation, published in the journal Brain, transformed EEG from a curiosity into a serious research tool.
Technical Improvements
Adrian and Matthews brought several methodological improvements to EEG recording:
- Superior signal amplification equipment
- Better electrical shielding to reduce noise
- Systematic protocols to rule out artifact sources
- Simultaneous recording from multiple electrode positions
Their technical rigor helped establish standards that would guide EEG research for decades.
Early Observations of Photic Influence
During their investigations, Adrian and Matthews made an observation that would become significant for entrainment research. They noted that flickering light could produce rhythmic responses in the visual cortex that matched the flicker frequency. While this was not their primary focus, this early documentation of photic driving provided a foundation for later systematic investigation of how external rhythmic stimuli might influence brain electrical activity.5
Following the 1934 confirmation, EEG rapidly spread to research laboratories and clinical settings worldwide. By the late 1930s, electroencephalography was being used to investigate epilepsy, brain tumors, and various neurological conditions. This expansion of EEG research created the conditions for more systematic investigation of brain-stimulus interactions.
1940s: Auditory Driving Experiments Begin
The 1940s saw researchers begin systematic investigation of how rhythmic auditory stimuli might influence brain electrical activity. The term "auditory driving" emerged to describe the observation that repetitive sounds could produce detectable changes in EEG recordings.
Early auditory driving experiments used simple repetitive sounds, such as clicks or tones presented at various rates. Researchers observed that certain frequencies of auditory stimulation could produce corresponding activity in EEG recordings, though the effects were generally smaller and less consistent than those observed with visual (photic) stimulation.6
Photic Driving
- Stronger, more consistent EEG responses
- Effects concentrated in visual cortex (occipital)
- Observed across wide frequency range
- Could trigger photosensitive seizures in susceptible individuals
- Easier to detect and measure
Auditory Driving
- Subtler, more variable EEG responses
- Effects in temporal and frontal regions
- More limited effective frequency range
- Generally considered safer for research use
- Required more sensitive detection methods
Methodological Challenges
Early auditory driving researchers faced several methodological challenges. Distinguishing genuine brain responses from auditory evoked potentials (normal neural responses to sound onset) proved difficult. Additionally, the relatively weak effects of auditory stimulation compared to photic stimulation made consistent results harder to achieve.
These challenges led some researchers to question whether auditory driving represented true entrainment (the brain's intrinsic oscillators synchronizing with external rhythms) or simply reflected normal auditory processing. This question would continue to be debated throughout the following decades.7
Scientific Caution
From the earliest auditory driving experiments, researchers recognized the importance of distinguishing between different types of brain responses to rhythmic stimuli. Not all rhythmic EEG activity in response to stimulation necessarily indicates true entrainment of intrinsic brain oscillators. This distinction remains relevant to contemporary research.
1959: Chatrian and Photic Driving Response
While photic driving had been observed since the 1930s, systematic characterization of the phenomenon advanced significantly with the work of researchers including G.E. Chatrian and colleagues. Their investigations in the late 1950s and early 1960s helped establish standardized methods for studying photic driving and documented the characteristics of normal and abnormal responses.8
The photic driving response (PDR) refers to the synchronization of EEG rhythms, particularly in the occipital (visual) cortex, with repetitive light flashes. Researchers found that PDR was strongest when the flash frequency was near the individual's natural alpha frequency (typically 8-12 Hz), and that harmonics and subharmonics of the stimulation frequency could also be observed in the EEG.
Photic Stimulation in EEG Testing
By the 1960s, photic stimulation had become a standard component of clinical EEG examinations. Flashing lights at various frequencies could reveal abnormal responses, helping diagnose photosensitive epilepsy and other neurological conditions. This clinical application demonstrated that brain-stimulus interactions had practical diagnostic value.
Individual Differences in Response
Researchers in this era documented substantial individual differences in photic driving responses. Some individuals showed strong, clear synchronization across a wide range of frequencies, while others showed minimal or no detectable response. These individual differences would later become important considerations in evaluating the potential applications of rhythmic stimulation.
The research also established important safety considerations. Photic stimulation at certain frequencies could trigger seizures in individuals with photosensitive epilepsy, leading to the development of safety protocols that remain relevant today. Frequencies in the 15-25 Hz range were identified as particularly likely to trigger photoparoxysmal responses in susceptible individuals.9
1970s: The Biofeedback Movement
The 1970s witnessed the emergence of the biofeedback movement, which brought EEG technology and concepts about brainwave states to broader public awareness. Biofeedback researchers investigated whether individuals could learn to voluntarily control their own physiological processes, including brain electrical activity, when provided with real-time feedback.
Alpha biofeedback, in particular, gained significant attention. Building on Berger's observations that alpha waves were associated with relaxed wakefulness, researchers investigated whether training individuals to increase their alpha activity might have psychological benefits. Joe Kamiya at the University of Chicago conducted pioneering work demonstrating that some individuals could learn to recognize when they were producing alpha waves and, to some degree, voluntarily increase alpha activity.10
Biofeedback vs. Entrainment
It's important to distinguish between two different approaches that emerged in this era:
- Biofeedback: Training individuals to voluntarily modify their own brain activity using real-time feedback
- Entrainment: Using external rhythmic stimuli to influence brain rhythms without requiring voluntary effort
Both approaches generated research interest and commercial applications, though they operate through different mechanisms.
Commercial Expansion and Criticism
The biofeedback movement saw rapid commercial expansion during the 1970s, with numerous companies marketing biofeedback devices to consumers. This commercialization occurred faster than the scientific evidence could support, leading to criticism from researchers who felt that claims were outpacing evidence.
Studies attempting to replicate early positive findings produced mixed results. Questions emerged about whether reported benefits were due to the biofeedback itself, relaxation induced by the training sessions, placebo effects, or other factors. These debates established patterns of hype, commercialization, and subsequent critical evaluation that would recur with later entrainment technologies.11
Lessons from the Biofeedback Era
The biofeedback movement of the 1970s established important precedents for evaluating brain-related technologies:
- The need for controlled studies to separate specific effects from placebo responses
- The importance of individual differences in response to brain-based interventions
- The tendency for commercial applications to outpace scientific evidence
- The value of maintaining scientific skepticism while remaining open to investigation
1973: Gerald Oster and Binaural Beats
A landmark publication in 1973 brought renewed attention to a previously obscure auditory phenomenon. Gerald Oster, a biophysicist at Mount Sinai School of Medicine, published "Auditory Beats in the Brain" in Scientific American, introducing binaural beats to a broader scientific and popular audience.12
Binaural beats are a perceptual phenomenon that occurs when two slightly different frequencies are presented separately to each ear through headphones. If one ear receives a 400 Hz tone and the other receives a 410 Hz tone, the listener perceives a third tone that pulses at 10 Hz, the difference between the two frequencies. This perceived beating is not present in the acoustic signal itself but is generated by the auditory system's processing of the two inputs.
Important Distinction: Binaural beats had actually been discovered in 1839 by Heinrich Wilhelm Dove, a Prussian physicist. Oster's 1973 article did not discover the phenomenon but rather synthesized existing knowledge and proposed new applications, particularly suggesting that binaural beats might be useful for investigating auditory processing and potentially for influencing brain states.
Oster's Proposals and Observations
Oster's article made several observations and proposals that would influence subsequent research and commercial development:
Frequency Range Limitations
Oster noted that binaural beats are only clearly perceived when the carrier frequencies are below approximately 1000 Hz and when the beat frequency (the difference between the two tones) is below approximately 30 Hz. Outside these ranges, the phenomenon either disappears or is perceived differently.
Individual Differences
The article documented substantial individual differences in binaural beat perception. Some individuals perceived the beats clearly, while others had difficulty detecting them. Oster suggested this variability might be diagnostically useful.
Proposed Applications
Oster speculated that binaural beats might be useful for various purposes, including investigating auditory neurophysiology and potentially influencing brain states. These speculations, though preliminary, helped spark interest in binaural beats as more than just an auditory curiosity.
Following Oster's publication, researchers began investigating whether binaural beats could influence EEG activity and subjective states. The results of these investigations have been mixed, with some studies reporting effects on measures such as anxiety or attention, while others found no significant effects or methodological limitations in positive studies.13
1990s: Digital Audio Revolution
The 1990s saw the convergence of several technological developments that dramatically expanded access to binaural beat and other entrainment audio. The widespread adoption of personal computers, CD audio, and eventually MP3 technology made it possible for anyone to create and distribute entrainment audio.
Companies such as Hemi-Sync (associated with The Monroe Institute) and others developed commercial products claiming various benefits from binaural beat audio. These products were marketed for relaxation, meditation enhancement, sleep improvement, and cognitive enhancement, among other purposes.
| Era | Technology | Access | Cost |
|---|---|---|---|
| 1970s-1980s | Specialized analog equipment | Research labs, specialty clinics | Thousands of dollars |
| 1990s | CD players, early personal computers | Commercial products available | $50-200 per program |
| 2000s | MP3 players, internet distribution | Widespread availability | $10-50 or free |
| 2010s-Present | Smartphone apps, streaming | Universal access | Free to subscription-based |
Expansion Beyond Binaural Beats
The 1990s also saw increased interest in other forms of auditory entrainment beyond binaural beats:
- Monaural beats: Two frequencies combined into a single audio signal, perceived without requiring headphones
- Isochronic tones: Single tones that pulse on and off at regular intervals
- Audiovisual entrainment (AVE): Combining pulsing sounds with flashing lights through specialized devices
Proponents argued that each approach had different characteristics and potential advantages. Monaural beats and isochronic tones do not require the brain to synthesize a beat from two inputs, which some suggested might produce stronger entrainment effects. Audiovisual entrainment devices combined photic and auditory stimulation, potentially leveraging the stronger effects of photic driving.14
Evidence vs. Marketing
The commercialization of entrainment technologies during the 1990s and 2000s often outpaced scientific evidence. Many products made claims that were not supported by peer-reviewed research, and some claims that were made could not be substantiated by independent investigation. This gap between marketing and evidence remains a challenge in evaluating entrainment products today.
2000s: Gamma Wave Research Accelerates
While early EEG research focused primarily on slower frequencies (alpha, theta, delta), the 2000s saw dramatically increased interest in gamma oscillations, typically defined as rhythmic brain activity in the 30-100 Hz range. Gamma activity had been observed in earlier research but was often dismissed as muscle artifact due to technical limitations.
Improved recording and analysis techniques allowed researchers to distinguish genuine gamma oscillations from artifacts, leading to a surge of interest in gamma's potential role in cognition. Studies investigated associations between gamma activity and attention, memory, consciousness, and perceptual binding (the brain's integration of different sensory features into coherent perceptions).15
40 Hz and Cognitive Research
Among the gamma frequencies, 40 Hz received particular attention. Researchers investigated associations between 40 Hz oscillations and various cognitive processes:
Gamma Oscillations and Cognition
Studies in the 2000s investigated correlations between gamma activity and cognitive processes. Increased gamma power and synchronization were observed during tasks involving attention, working memory, and sensory integration. However, whether gamma activity plays a causal role in these processes, or is simply a correlate, remains an active area of investigation.
The renewed interest in gamma oscillations naturally led researchers to investigate whether gamma-frequency stimulation might influence cognition or brain function. This research built on the earlier foundation of entrainment studies, now with specific focus on the higher frequency ranges associated with active cognition.
Challenges in Gamma Entrainment Research
Investigating gamma entrainment presented specific challenges:
- Auditory limitations: Pure auditory beats at gamma frequencies (e.g., 40 Hz) are not easily perceived, requiring alternative approaches such as amplitude modulation
- Artifact concerns: Recording genuine gamma activity requires careful methodology to distinguish brain signals from muscle artifacts
- Safety considerations: Photic stimulation in the gamma range requires attention to photosensitive epilepsy risks
- Individual variability: Responses to gamma stimulation vary considerably between individuals
2016: MIT Tsai Lab 40Hz Study
In December 2016, a study from Li-Huei Tsai's laboratory at MIT generated significant scientific and media attention. Published in Nature, the study by Iaccarino et al. investigated the effects of 40 Hz light stimulation in mouse models of Alzheimer's disease.16
The researchers reported that exposing mice to flickering light at 40 Hz for one hour per day led to reduced amyloid-beta (a protein associated with Alzheimer's disease pathology) in the visual cortex of the treated animals. They proposed that the stimulation enhanced the activity of microglia (brain immune cells) and promoted amyloid clearance.
Iaccarino et al. 2016 Study
Key findings in mouse models:
- 40 Hz light flicker induced gamma oscillations in the visual cortex
- One hour of daily stimulation reduced amyloid-beta levels in visual cortex
- Microglia showed altered morphology suggesting increased phagocytic activity
- Effects were frequency-specific (40 Hz showed effects, other frequencies did not)
Important caveats: These were mouse model studies. Effects in humans may differ substantially, and the translation from animal models to clinical applications requires extensive additional research.
Subsequent Research and Human Studies
The Tsai lab publication sparked increased research interest in 40 Hz stimulation. Follow-up studies from the same laboratory and others have investigated:
- Combined audiovisual stimulation at 40 Hz
- Effects on additional brain regions beyond visual cortex
- Safety and tolerability in human subjects
- Potential effects on cognitive measures in humans
Early human studies have investigated safety, tolerability, and feasibility of 40 Hz stimulation in people with and without cognitive impairment. Several clinical trials are ongoing to evaluate whether the effects observed in mouse models translate to meaningful benefits in humans. As of the knowledge cutoff for this article, definitive conclusions about clinical efficacy in humans are not yet available.17
Ongoing Research
The translation from mouse model findings to human clinical applications is a lengthy process. While the Tsai lab research has generated substantial interest and prompted further investigation, claims about clinical benefits in humans should be evaluated cautiously pending results from properly controlled clinical trials. The history of medical research includes many examples of promising animal model results that did not translate to human benefit.
2010s-Present: Commercial Applications and Ongoing Research
The current landscape of brainwave entrainment encompasses both continued scientific investigation and widespread commercial applications. Smartphone apps offering binaural beats and other entrainment audio number in the hundreds, with millions of downloads. Some products incorporate claims based on the 40 Hz research, though the evidence supporting consumer-level implementations remains limited.
Current Research Directions
Contemporary research continues to investigate fundamental questions about entrainment:
Mechanisms of Action
Researchers continue investigating how external rhythmic stimulation might influence brain activity. Questions remain about whether observed effects represent true entrainment of intrinsic neural oscillators, evoked responses to repeated stimuli, or other mechanisms.
Individual Differences
Understanding why some individuals respond more strongly to entrainment stimulation than others is an active area of investigation. Factors including baseline brain activity patterns, attention, and auditory processing may contribute to response variability.
Clinical Applications
Clinical trials are investigating potential applications of entrainment in conditions including Alzheimer's disease, anxiety, depression, and sleep disorders. These studies aim to determine whether observed effects translate to clinically meaningful benefits.
Commercial Landscape
The consumer market for entrainment products has expanded dramatically:
- Mobile applications: Hundreds of apps offering binaural beats, isochronic tones, and related audio
- AVE devices: Hardware devices combining light and sound stimulation
- Specialized headphones: Products claiming to enhance entrainment through specific acoustic designs
- Neurofeedback systems: Combining entrainment with real-time brain activity feedback
The regulatory status of these products varies by jurisdiction. Most are marketed as wellness or relaxation tools rather than medical devices, allowing them to avoid the rigorous testing required for therapeutic claims.
Historical Timeline of Brainwave Entrainment Research
The following timeline summarizes key milestones in the history of brainwave entrainment research:
Discovery of Binaural Beats
Heinrich Wilhelm Dove discovers binaural beats, though the phenomenon remains a scientific curiosity for over a century.
First Human EEG Publication
Hans Berger publishes "On the Electroencephalogram of Man," documenting alpha and beta waves.
EEG Validation
Adrian and Matthews confirm Berger's findings, establishing EEG as a legitimate research tool.
Auditory Driving Research Begins
Systematic investigation of how rhythmic sounds influence brain electrical activity.
Photic Driving Standardization
Researchers characterize photic driving response; photic stimulation becomes standard in clinical EEG.
Biofeedback Movement
Alpha biofeedback gains public attention; early commercialization of brain-related technologies.
Oster's Scientific American Article
Gerald Oster publishes "Auditory Beats in the Brain," bringing binaural beats to wider attention.
Digital Audio Revolution
CD and MP3 technology enables widespread distribution of entrainment audio products.
Gamma Wave Research Expansion
Improved recording techniques enable greater focus on gamma oscillations and cognition.
MIT Tsai Lab 40Hz Study
Iaccarino et al. publish findings on 40 Hz light stimulation in mouse models of Alzheimer's disease.
Ongoing Clinical Investigation
Human clinical trials investigate potential therapeutic applications; consumer products proliferate.
The history of brainwave entrainment research demonstrates both the scientific curiosity that drives investigation of brain-stimulus interactions and the tendency for commercial applications to emerge ahead of definitive evidence. As research continues, our understanding of when and how external rhythmic stimuli might influence brain activity will continue to evolve.
References
- Berger, H. (1929). Uber das Elektrenkephalogramm des Menschen. Archiv fur Psychiatrie und Nervenkrankheiten, 87, 527-570.
- Millett, D. (2001). Hans Berger: From psychic energy to the EEG. Perspectives in Biology and Medicine, 44(4), 522-542. https://pubmed.ncbi.nlm.nih.gov/11600799/
- Gloor, P. (1969). Hans Berger on the electroencephalogram of man. Electroencephalography and Clinical Neurophysiology, Suppl 28:1-350.
- Adrian, E. D., & Matthews, B. H. (1934). The Berger rhythm: Potential changes from the occipital lobes in man. Brain, 57(4), 355-385. https://academic.oup.com/brain/article-abstract/57/4/355/331779
- Adrian, E. D., & Matthews, B. H. (1934). The interpretation of potential waves in the cortex. The Journal of Physiology, 81(4), 440-471. https://pubmed.ncbi.nlm.nih.gov/16994555/
- Toman, J. (1941). Flicker potentials and the alpha rhythm in man. Journal of Neurophysiology, 4(1), 51-61.
- Neher, A. (1961). Auditory driving observed with scalp electrodes in normal subjects. Electroencephalography and Clinical Neurophysiology, 13(3), 449-451. https://pubmed.ncbi.nlm.nih.gov/13783668/
- Chatrian, G. E., Bergamini, L., Dondey, M., et al. (1974). A glossary of terms most commonly used by clinical electroencephalographers. Electroencephalography and Clinical Neurophysiology, 37(5), 538-548. https://pubmed.ncbi.nlm.nih.gov/4138726/
- Fisher, R. S., Harding, G., Erba, G., et al. (2005). Photic- and pattern-induced seizures: A review for the Epilepsy Foundation of America Working Group. Epilepsia, 46(9), 1426-1441. https://pubmed.ncbi.nlm.nih.gov/16146439/
- Kamiya, J. (1968). Conscious control of brain waves. Psychology Today, 1(11), 56-60.
- Plotkin, W. B. (1976). On the self-regulation of the occipital alpha rhythm: Control strategies, states of consciousness, and the role of physiological feedback. Journal of Experimental Psychology: General, 105(1), 66-99. https://pubmed.ncbi.nlm.nih.gov/1255268/
- Oster, G. (1973). Auditory beats in the brain. Scientific American, 229(4), 94-102. https://www.scientificamerican.com/article/auditory-beats-in-the-brain/
- Wahbeh, H., Calabrese, C., & Zwickey, H. (2007). Binaural beat technology in humans: A pilot study to assess psychologic and physiologic effects. The Journal of Alternative and Complementary Medicine, 13(1), 25-32. https://pubmed.ncbi.nlm.nih.gov/17309374/
- Huang, T. L., & Charyton, C. (2008). A comprehensive review of the psychological effects of brainwave entrainment. Alternative Therapies in Health and Medicine, 14(5), 38-50. https://pubmed.ncbi.nlm.nih.gov/18780583/
- Herrmann, C. S., Munk, M. H., & Engel, A. K. (2004). Cognitive functions of gamma-band activity: Memory match and utilization. Trends in Cognitive Sciences, 8(8), 347-355. https://pubmed.ncbi.nlm.nih.gov/15335461/
- Iaccarino, H. F., Singer, A. C., Martorell, A. J., et al. (2016). Gamma frequency entrainment attenuates amyloid load and modifies microglia. Nature, 540(7632), 230-235. https://www.nature.com/articles/nature20587
- Chan, D., Suk, H. J., Jackson, B., et al. (2021). Gamma frequency sensory stimulation in probable mild Alzheimer's dementia patients: Results of a preliminary clinical trial. medRxiv. https://www.medrxiv.org/content/10.1101/2021.03.01.21252717v1
Disclaimer: This article is for educational purposes only and does not constitute medical advice. The historical information presented describes what researchers investigated, not necessarily what has been proven effective. Brainwave entrainment products are not approved medical devices. Individuals with epilepsy or other neurological conditions should consult healthcare professionals before using any form of rhythmic light or sound stimulation. NullField Lab is a research tool for personal experimentation, not a medical device.
