Huang & Charyton (2008): A Comprehensive Review of the Psychological Effects of Brainwave Entrainment

In 2008, Tina L. Huang and Christine Charyton published one of the most frequently cited early reviews of the psychological effects of brainwave entrainment. Their article brought together twenty experimental and quasi-experimental studies involving rhythmic auditory stimulation, photic stimulation or a combination of both. The review reported promising findings across cognition, stress and anxiety, pain, headaches, mood, behaviour and premenstrual symptoms.

The paper is historically important because it treated brainwave entrainment as a research field rather than a single device or frequency. It also made the topic accessible to clinicians and researchers who were unfamiliar with rhythmic sensory stimulation. At the same time, its positive conclusion must be read alongside the authors’ own call for more controlled trials and alongside methodological knowledge developed since 2008.

The responsible interpretation is neither “the review proved that brainwave entrainment works for everything” nor “the early evidence was meaningless.” It identified a broad, promising research signal that required better standardisation and stronger confirmation.

The study at a glance

Why this 2008 review became influential

At the time, research on rhythmic sensory stimulation was scattered across terminology, disciplines and application areas. One paper might describe auditory driving, another audiovisual stimulation, photic stimulation or binaural beats. Psychological outcomes were equally diverse. Huang and Charyton attempted to gather this fragmented literature under the broader concept of brainwave entrainment.

That broad approach was useful because modern discussions sometimes reduce brainwave entrainment to binaural beats alone. The 2008 review included protocols using auditory and/or photic stimulation and considered single, alternating, ascending, descending and participant-selected frequencies. It therefore described a family of interventions rather than one standardised treatment.

What question did Huang and Charyton ask?

The stated objective was to raise awareness of brainwave entrainment and discuss its potential by systematically reviewing peer-reviewed literature on psychological effects. The focus was practical: did rhythmic stimulation influence outcomes that people could experience or that researchers could assess psychologically?

This is different from asking whether EEG activity reliably follows every delivered rhythm. In fact, the review explicitly did not include physiological outcomes such as EEG response, galvanic skin response or neurotransmitter levels in its data synthesis. It reviewed psychological outcomes, not the complete neurophysiological mechanism.

How was the literature searched?

The authors searched English-language studies in three major databases: OVID Medline covering 1950–2007, PsycINFO covering 1806–2007 and Scopus. They used terms describing brainwave entrainment and psychological outcomes. This multi-database strategy was a meaningful strength for an emerging field with inconsistent terminology.

Only peer-reviewed experimental and quasi-experimental research was eligible. Case studies and other review articles were excluded. The studies needed to use rhythmic stimuli with the intention of affecting psychological outcomes, and those outcomes needed to be measured through standard assessment methods or methods considered appropriate through peer review.

• The review did not simply collect testimonials.
• It required experimental or quasi-experimental research.
• It accepted a wide range of brainwave-entrainment formats.
• It focused on psychological rather than physiological endpoints.
• It included both single-session and repeated-session interventions.
• It ultimately selected twenty studies.

What kinds of protocols were included?

The included research did not test one identical intervention. Some studies used auditory stimulation, some used photic stimulation and others combined sensory channels. Frequencies could remain constant, alternate, rise, descend or be selected in relation to the participant.

The exposure schedule also varied. Some studies examined immediate effects after a single session; others examined multiple sessions over time. This breadth helped the review map the field, but it also makes a single combined conclusion harder to interpret. A five-minute auditory experiment and a multi-session audiovisual programme should not automatically be treated as equivalent interventions.

Which psychological outcomes were reported?

According to the review abstract, the included studies addressed cognition, stress and anxiety, pain relief, headaches or migraine, mood, behaviour and premenstrual syndrome. These domains are broad and should not be interpreted as one single clinical outcome.

Cognition

Cognition may refer to attention, memory, processing, task performance or functioning in people with cognitive difficulties. A positive result in one cognitive task does not prove a general increase in intelligence or learning ability. The review’s contribution was to show that cognition had been investigated and that some studies reported benefit.

Stress and anxiety

Rhythmic stimulation may influence subjective arousal through sound, expectation, attention, breathing and the structured rest period itself. The review found encouraging psychological outcomes in this area, but it did not establish brainwave entrainment as a replacement for evidence-based treatment of anxiety disorders.

Pain, headache and migraine

Pain is shaped by sensory, attentional, emotional and contextual processes. A change in perceived pain is clinically interesting, but it does not automatically reveal the mechanism or treat the underlying cause. Migraine is also especially relevant to safety because some people are sensitive to light or flicker.

Mood and behaviour

Mood and behaviour are influenced by many variables, including environment, music, expectancy and interpersonal context. The review’s positive signal justified further research, but broad labels do not tell us which protocol works for which person, under which conditions or for how long.

Premenstrual symptoms

The inclusion of premenstrual syndrome illustrates the breadth of the early literature. It should not be used to claim that brainwave entrainment treats hormonal or gynaecological conditions. At most, it indicates that psychological or symptom-related outcomes had been studied in that context.

What did the authors conclude?

Huang and Charyton concluded that findings available at the time suggested brainwave entrainment was an effective therapeutic tool. They wrote that people with cognitive functioning deficits, stress, pain, headache or migraine, premenstrual symptoms and behavioural problems had benefited in the reviewed studies.

The next sentence is essential: the authors stated that more controlled trials were needed to test additional protocols and outcomes. Their conclusion was positive, but not final. It was an invitation to develop the evidence base rather than permission to treat every frequency claim as established.

The strengths of the review

• It systematically searched several major databases.
• It focused on peer-reviewed experimental evidence.
• It excluded case reports and previous reviews.
• It recognised brainwave entrainment as more than binaural beats alone.
• It covered auditory, photic and combined protocols.
• It separated psychological outcomes from physiological measurements.
• It highlighted both immediate and repeated-session research.
• It clearly called for additional controlled trials.

For 2008, this was an important act of research organisation. It created a reference point that later authors could support, refine or challenge.

Important limitations and cautions

Twenty studies are informative but not definitive

Twenty studies can reveal patterns, but the reliability of a review depends on the design, sample size and bias risk of those studies. The abstract does not report a pooled effect size or demonstrate that all included outcomes were supported equally strongly.

The interventions were highly heterogeneous

Auditory stimulation, photic stimulation, combined audiovisual programmes, different frequencies and different exposure schedules may work through partly different mechanisms. Broad inclusion maps the field but limits the precision of recommendations.

Experimental and quasi-experimental evidence were combined

Quasi-experimental research can be useful, especially in emerging fields, but generally offers less protection against selection effects and confounding than rigorous randomised controlled trials. The review’s call for more controlled work follows logically from this limitation.

English-language restriction may introduce bias

Searching only English-language studies may miss relevant findings and can contribute to language bias. This was common in older reviews but should still be recognised when interpreting completeness.

The review did not synthesise EEG evidence

This is one of the most misunderstood points. Positive psychological outcomes do not automatically demonstrate that electrocortical activity matched the external frequency. The review deliberately excluded EEG response and other physiological measures from its data extraction.

Publication date matters

The search ended in 2007. The article cannot evaluate studies, reporting standards and technologies developed afterward. It remains historically valuable but should not be used alone as a complete account of current evidence.

Affiliation and transparency

PubMed lists Tina Huang’s affiliation as Transparent Corporation in Columbus, Ohio. An industry-related affiliation does not invalidate research, but it is relevant context and reinforces the importance of independent replication, transparent methods and careful conflict-of-interest reporting.

PubMed also records an erratum published in the following issue of the journal. The database entry does not describe the correction in its abstract, so readers who require exact historical detail should consult the journal record.

What later research added

Later research did not produce one simple verdict. Instead, it refined the picture. Some reviews and meta-analyses reported statistically significant average effects, while other reviews emphasised inconsistent EEG entrainment and major methodological heterogeneity.

2019 meta-analysis of binaural beats

Garcia-Argibay and colleagues included twenty-two studies and reported an overall medium significant effect across cognition, anxiety and pain perception. They also found that timing, duration and frequency appeared to influence outcomes. This supported continued interest, but the analysis concerned binaural beats specifically and should not automatically be generalised to every audiovisual protocol.

2023 review of memory and attention

Basu and Banerjee analysed fifteen studies and found a near-moderate average effect for memory and attention, while their systematic review still identified conflicting findings, particularly for theta and beta protocols. Their conclusion again combined promise with a call for stronger designs.

2023 review of EEG entrainment by binaural beats

Ingendoh and colleagues focused on whether binaural beats produced the expected changes in brain oscillatory activity. Of fourteen included studies, five reported results consistent with the entrainment hypothesis, eight reported contradictory results and one reported mixed findings. The authors emphasised major differences in stimulation, design and EEG analysis.

This does not negate psychological effects. It shows that a beneficial subjective or behavioural outcome and proof of frequency-specific cortical entrainment are separate scientific questions.

2025 integrative review

A more recent integrative review included eighty-four studies published across the preceding decade and reported promising findings in areas including pain, sleep, mood and cognition. It again called for larger samples, robust control groups and randomised clinical trials. One author disclosed being founder and CEO of a brainwave-technology company, which is relevant context when weighing conclusions.

What the Huang and Charyton review does support

• Brainwave entrainment had a peer-reviewed experimental literature before 2008.
• The field covered more than one sensory technique or frequency.
• Psychological outcomes had been investigated in several domains.
• The evidence contained promising positive findings worth following up.
• Single-session and repeated-session approaches both deserved study.
• Better controlled and more standardised research was necessary.

What the review does not prove

• It does not prove that every person responds to brainwave entrainment.
• It does not establish one best frequency for a psychological outcome.
• It does not prove that psychological change was caused by EEG entrainment.
• It does not validate all commercial mind-machine claims.
• It does not show that brainwave entrainment replaces medical or psychological treatment.
• It does not make all auditory and visual protocols equivalent.
• It does not provide a modern safety assessment for every device or population.

How professionals can use this review responsibly

The review is best used as historical and conceptual support for careful experimentation. A professional can explain that research has examined psychological outcomes for decades, while also stating that protocols and evidence quality vary.

• Define one intended use rather than claiming broad treatment effects.
• Use the lowest comfortable audio and light intensity.
• Track relevant outcomes instead of relying only on expectation.
• Distinguish relaxation, performance support and medical treatment.
• Avoid inferring a brain state solely from the delivered hertz value.
• Document adverse responses and stop criteria.
• Update claims when stronger evidence becomes available.

Readers interested in practical session design can explore the NeuroSync Pro® categories for Focus & Concentration, Relaxation, Sleep and Meditation. These session articles describe design intentions and safety without treating one historical review as proof of guaranteed outcomes.

Safety and medical boundaries

NeuroSync Pro® is not a medical device. Brainwave entrainment does not diagnose, treat, cure or prevent cognitive disorders, anxiety disorders, migraine, chronic pain, premenstrual syndrome, depression or behavioural disorders. The 2008 review should not be used to replace diagnosis or evidence-based care.

• Do not use rhythmic light with photosensitive epilepsy, seizure disorders or unexplained loss of consciousness without medical clearance.
• Do not use entrainment while driving, cycling, operating machinery or performing safety-critical activities.
• Stop with headache, visual symptoms, nausea, panic, agitation, derealisation or dissociation.
• Use caution with migraine and sensory sensitivity; audio-only may be preferable.
• Seek qualified care for persistent pain, severe headaches, disabling anxiety, cognitive decline or other significant symptoms.

Frequently asked questions

Was Huang and Charyton (2008) an experiment?

No. It was a systematic review of twenty previously published experimental and quasi-experimental studies.

Was it a meta-analysis?

PubMed classifies it as a systematic review. The abstract does not report a pooled statistical effect size, so it should not be described as a quantitative meta-analysis.

Did the review prove brainwave entrainment changes EEG?

No. EEG and other physiological measures were explicitly excluded from the review’s data extraction. It focused on psychological outcomes.

Why is the review still cited?

It was an early systematic attempt to organise a fragmented field and showed that brainwave entrainment had been experimentally studied across several psychological domains.

Is its conclusion still current?

Its description of promising evidence remains historically relevant, but the evidence base has expanded. Modern interpretation should include later reviews showing both positive average effects and substantial inconsistency.

Can the review justify medical claims?

No. A broad review of early psychological outcomes is not sufficient to claim diagnosis, treatment or cure of a medical condition.

Conclusion: an important foundation, not the final word

Huang and Charyton’s 2008 review deserves its place in the history of brainwave-entrainment research. It showed that rhythmic auditory and visual stimulation had already been studied in relation to a diverse set of psychological outcomes and that positive findings were substantial enough to justify serious attention.

Its lasting message is not that one frequency solves one problem. The lasting message is that rhythmic sensory stimulation is a legitimate subject for experimental research, that psychological effects are possible and that protocol quality matters. The equally important second message is the authors’ own: more controlled trials were needed.

For NeuroSync Pro®, this supports a research-informed approach: carefully designed sessions, transparent language, individual response monitoring and claims that remain proportional to the evidence. Learn more about the technology on the NeuroSync Pro homepage.

Primary publication and further reading

• Huang & Charyton (2008): original PubMed record
• Garcia-Argibay et al. (2019): meta-analysis of cognition, anxiety and pain
• Basu & Banerjee (2023): meta-analysis and review of memory and attention
• Ingendoh et al. (2023): systematic review of binaural beats and EEG entrainment
• Cidral-Filho et al. (2025): integrative review of brainwave entrainment

This article is an educational interpretation based primarily on the indexed abstract and bibliographic record of the original publication, supplemented by later peer-reviewed reviews. It is not a substitute for reading the full paper or for professional medical and scientific advice.