Brainwave Entrainment

Posted: 2024-09-15
Tags: Brain

Brainwave entrainment is the phenomena that large-scale brainwave oscillations will synchronize with an external rhythmic stimulii (flashing lights or pulsing audio).

Actionable Takeaways

There is mixed (but generally positive) evidence for entrainment’s effectiveness, and no negative side-effects have been noted.

Binaural and isochronic beats are widely available for no cost, so anyone interested in it should try several to see if they experience benefits.

When attempting brainwave entrainment, begin exposure to the rhythmic stimuli BEFORE beginning the task and continue the stimuli while working on the task1.

Two specific findings:

Defining Terms

“Brainwaves” are a crude measure of the rate of individual neuron activations over time. Brainwaves do not give a clear indication of anything other than a large amount of individual neurons firing at the same time.

Simulation of Neural Oscillations

Isochronal (or isochronic) tones are audio tones with a constant, regular beat. From the Greek, “iso-chronal” being “equal-time”.

Monaural beats are regular audio beats.

Binaural beats use two slightly different audio tones, one into each ear. The difference between the two frequencies is perceived by the brain.

Usefulness of Binaural Beats

Under ideal conditions, humans can hear a range of sounds from 12 Hz to 20,000 Hz.2 This is reduced with age and hearing damage.

Cheap audio systems have difficulty producing strong bass (low frequency) tones, and some desirable frequencies are below the perceptual threshold.

Binaural beats can be used to generate a percieved beat at frequencies from 1 Hz to about 30 Hz.3 This allows auditory stimulation in ranges that could not be perceived with simple isochronal/monaural beats.

Note: Binaural beats are an illusory phenomenon. Their perceptual basis is not the interference of two sound waves, but a result of their combined neural activity elicited in the auditory pathway. The superior olivary complex (SOC), the first locus of the auditory pathway to receive input from both ears and an important structure for sound integration, has been identified as the main neuroanatomical structure involved in binaural beat perception.3

Restrictions on Binaural Beats3

To elicit a binaural beat, the two presented frequencies should be below 1000 Hz.

Beats seem to be best perceived at carrier frequencies (the frequencies of the two presented tones) of around 400 Hz.

The maximum difference for the two tones must be around 30 Hz. Beyond frequency differences of 30 Hz, the two tones are perceived separately instead of eliciting the perception of a binaural beat.

Up to 20 Hz, the binaural beat is described as a tone fluctuating in loudness, while frequency differences larger than 20 Hz elicit a rough sound.

Below a difference of 3 Hz, the binaural beat is perceived as a rotating tone (a sound that appears to rotate in the head from ear to ear).

These thresholds are approximate and assumed to vary interindividually.

The Research

Several meta-analyses have been done on the topic34156, most focus on binaural beats3456.

Anti-cognitive Decline

https://blog.szynalski.com/2018/03/40-hz-tone-alzheimers/comment-page-1/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6774262/ https://pubmed.ncbi.nlm.nih.gov/11409739/

Sleep

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9909225/ https://ncbi.nlm.nih.gov/pmc/articles/PMC9125055/ https://pubmed.ncbi.nlm.nih.gov/17309374/ https://pubmed.ncbi.nlm.nih.gov/17388762/

Random

https://hearinghealthmatters.org/pathways-society/2017/contralateral-ear-effect-tests-central-auditory-function-introduction/ https://www.simplypsychology.org/left-brain-vs-right-brain.html

  1. A comprehensive review of the psychological effects of brainwave entrainment Meta-analysis, any form of rhythmic stimuli. ↩ ↩2

  2. Wikipedia – Hearing Range - Humans ↩

  3. 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 Meta-analysis, focused on binaural beats. Fourteen studies met inclusion criteria: five reported positive results, eight negative results, and one with mixed results. ↩ ↩2 ↩3 ↩4 ↩5

  4. Potential of binaural beats intervention for improving memory and attention: insights from meta-analysis and systematic review Meta-analysis, focused on binaural beats. ↩ ↩2

  5. Efficacy of binaural auditory beats in cognition, anxiety, and pain perception: a meta-analysis Meta-analysis, focused on binaural beats. Twenty-two studies met inclusion criteria. Findings suggest that binaural-beat exposure “before” and “before and during” a task produces superior results than exposure “during” the task. ↩ ↩2

  6. Auditory Beat Stimulation and its Effects on Cognition and Mood States Meta-analysis. Covers monaural and binaural beats, with a focus on binaural. Thirty studies met inclusion criteria. ↩ ↩2