Audio-Visual Entrainment

Audio-visual entrainment

Few clinicians have heard of brainwave entrainment. The term brainwave entrainment refers to the use of rhythmic stimuli with the intention of producing a frequency-following response of brainwaves to match the frequency of the stimuli. The stimulus is usually either visual (flashing lights) or auditory (pulsating tones). By those in the industry, it is also commonly called "brain entrainment," "audiovisual entrainment (AVE)," "audiovisual stimulation (AVS)," "auditory entrainment," or "photic stimulation."

AVE is provided to the user in the form of a device that often includes goggles with light-emitting diodes (LEDs) and/or auditory sounds, usually requiring the use of headphones. Sessions usually last from 20-60 minutes. The most commonly used methods of AVE are to stimulate the brain at the desired frequency via auditory tones, flashing lights, or a combination of both. The 3 most common forms of auditory stimulation use isochronic, monaural, or binaural beats. Isochronic tones are evenly spaced tones that simply turn on and off. Monaural and binaural beats are presented as 2 tones with very similar frequencies, and the brain perceives a beat that is the difference between the 2 pitches. The pitches are presented together with monaural beats but fed separately to each ear with binaural beats. For photic stimulation, most devices use goggles with lights or a flashing screen, and most instructions suggest that the user's eyes remained closed. Pulses of light can be presented as different waveforms or colors. Photic stimulation also can be presented independently to each eye or each visual field in order to more effectively target stimulation to the right or left hemisphere.

Research into AVE

One of the earliest studies by Adrian and Mathews (1934) showed that the alpha rhythm could be  amplified by photic stimulation at the same frequency. In 1942, Dempsey and Morison found that AVE could also be induced by a tactile stimulus, and Chaitran reported entrainment effects with an auditory stimulus in 1959. Since then research on the effects of AVE on pain, headaches, migraines, anxiety, and stress followed in the 1980s and expanded in the 1990s to include learning and memory, ADHD, learning disabilities, behavioral problems, and PMS.

Research shows that presentation of a consistent rhythmic stimulus  within 8 to 10 Hz causes brainwaves in the occipital lobe, parietal lobe, or temporal cortex to exhibit a frequency-following response that either resonates with the presenting stimulus or shows a frequency harmonic or a sub-harmonic of a stimulus. Although many believe that the same mechanism applies to other frequencies, this has been harder to substantiate.

Cognitive functioning & AVE

One study that examined verbal abilities in school-aged children with ADHD used a protocol that alternated between alpha (10 Hz) and beta (15-18 Hz) AVE and found significant increases with a standardized reading test

Nonverbal skills were examined in 30 children were alternately exposed to an excitatory program (starting at 14 Hz and increasing to 40 Hz) and an inhibitory program (which started at 40 Hz and decreased to 14 Hz) over 6 weeks. These children showed a significant improvement with arithmetic using WISC-III, suggesting that incorporation of gamma frequencies (38-42 Hz) should be examined further as a potential method to improve nonverbal skills such as math.

Four studies that used a protocol that involved beta stimulation found significant improvements in attention using the Tests of Variable Attention (TOVA) or the WISC, but a study that used theta stimulation found no improvements.

Two studies used photic stimulation with or without electrodermal stimulation (EDR) at different frequencies to examine its effect on general intelligence or GPA. The studies selected children with ADHD or college students with "academic challenges" and found that stimulation of 14 Hz alternating with 22 Hz or 12 to 14 Hz over multiple sessions resulted in significant improvements on GPA or the Scholastic Achievement Wechsler Individual Achievement Test.

 

References for AVE

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