Audio-Visual Entrainment
Encyclopedia
Audio-visual entrainment (AVE), a subset of brainwave entrainment, uses flashes of lights and pulses
of tones
to guide the brain
into various states of brainwave activity. AVE devices are often termed light and sound machines or mind machines. Altering brainwave activity is believed to aid in the treatment of psychological and physiological disorders
.
via the thalamus
, and because the thalamus is highly innervated with the cortex, sensory stimulation can easily influence cortical activity. In order to affect brain (neuronal) activity, sensory stimulation must be within the frequency
range of roughly 0.5 to 25 hertz
(Hz). Touch, photic and auditory stimulation are capable of affecting brain wave activity. A large area of skin must be stimulated to affect brainwaves, which leaves both auditory and photic stimulation as the most effective and easiest means of affecting brain activity. Therefore, mind machines are typically in the form of light and sound devices.
Auditory or visual stimulation (AVS) can take a variety of forms, generating different subjective and clinical effects. The simplest form of stimulation is to present a series of random light flashes and/or sound pulses to a subject, such as from watching TV or cars drive by, and investigate the resulting subjective experiences or electroencephalography
(EEG) effects. AVE, however, involves organized, repetitive stimulation at a particular frequency for a specific period of time, and the frequency of stimulation is reflected within the EEG. This is called "open loop" stimulation, or free-running entrainment, and is not contingent on monitoring brainwaves in any way. "Close loop" AVE would involve visual and auditory stimulation in response to one's EEG.
, at the Salpêtrière Hospital
in France, reported that by having his patients gaze into the flickering light
produced from a spinning, spoked wheel in front of a kerosene lantern, they showed a reduction in their anxiety
and hysteria
. With the development of the EEG, Adrian and Matthews published their results showing that the alpha rhythm could be "driven" above and below the natural frequency with photic stimulation. This discovery prompted several small physiological outcome studies on the "flicker-following response," the brain's electrical response to repetitive stimulation As EEG equipment improved, so did a renewed interest in the brain's evoked response to photic and auditory entrainment and soon, a variety of studies were completed.
In 1956, W. Gray Walter published the first results on thousands of test subjects comparing flicker stimulation with the subjective emotional feelings it produced. Test subjects reported all types of visual illusions and in particular, the "whirling spiral" which was significant with alpha production. In the late 1950s, as a result of Kroger's observations as to why US military radar operators often drifted into trance
, Kroger teamed up with Sidney Schneider of the Schneider Instrument Company. They produced the world's first electronic clinical photic stimulator - the Schneider Brain Wave Synchronizer. It had powerful hypnotic qualities and soon studies on hypnotic induction were published A variety of companies developing AVE (light and sound) devices have been established since this time.
AVE consists of constant, repetitive stimuli of the proper frequency and sufficient strength to "excite" the thalamus and neocortex
. These stimuli do not transfer energy directly into the cortex. The direct transmission of energy from AVE only goes so far as to excite retinal cells in the eyes and pressure sensitive cilia within the cochlea
in the ears
. The nerve pathways from the eyes and ears carry the elicited electrical potentials into the thalamus. From there, the entrained electrical activity within the thalamus is "amplified" and distributed throughout other limbic areas and the cerebral cortexes via the cortical thalamic loop. AVE involves the continuous electrical response of the brain in relation to the stimulus frequency plus the mathematical representation (harmonics) of the stimulus wave shape.
(somatosensory) regions and slightly less within the prefrontal cortex.
It is within these areas where motor activation, attention
, executive function, and somatosensory (body) awareness is primarily mediated. Auditory entrainment (AE) is the same concept as visual entrainment, with the exception that auditory signals are passed from the cochlea of the ears into the thalamus via the medial geniculate nucleus
, whereas visual entrainment passes from the retina into the thalamus via the lateral geniculate nucleus
. Eyes-closed AVE at 18.5 Hz has been shown to increase EEG brainwave activity by 49% at the vertex. At the vertex (with the eyes closed) AE has been shown to increase EEG brainwave activity by 21%. Successful entrainment leads to a meditative, peaceful kind of dissociation, where the individual experiences a loss of somatic and cognitive awareness. However, it is possible for visual entrainment to trigger seizures.
or lysergic acid
. In his view, the rhythms of the lamp interacted with the rhythms of the brain's electrical activity to produce a complex interference pattern, which is translated by the brain's perceptual circuits into a conscious pattern of color
and movement
. Glicksohn also reported on altered states of consciousness from photic driving and its relationship of self-perceived creativity.
Other studies have shown that stimulation can produce both transient and lasting changes in the EEG. Collura
articulated the relationship between the low-frequency and high-frequency components of the steady-state visual evoked potential as reflecting anatomically and physiologically distinct response mechanisms.
Additional clinical studies explored the use of photic entrainment to induce hypnotic trance, to augment anasthesia during surgery, and to reduce pain, control gagging and accelerate healing in dentistry
. More recently, the induction of dissociation
was explored, which aided the understanding of dissociative pathology and development of better techniques for relaxing people suffering from trauma and posttraumatic stress disorder.
Dissociation begins after approximately four to eight minutes from properly applied AVE. A restabilization effect occurs where muscles relax, electro-dermal activity decreases, peripheral blood flow stabilizes, breathing becomes diaphragmatic and relaxed, and heart rates becomes uniform and smooth. Visual entrainment alone, in the alpha frequency range (7–10 Hz), has been shown to easily induce hypnosis, and it has been shown that nearly 80% of subjects entered into either a light or deep hypnotic trance within six minutes during alpha AVE. AVE provides an excellent medium for achieving an altered state of consciousness.
The results of a study on children with attention-deficit disorder found that AVE was more effective than neurofeedback for treating ADD symptoms.
A migraine headache study involving seven migraine sufferers found that AVE sessions reduced migraine duration from a pretreatment average of 6 hours to a posttreatment average of 35 minutes. Measuring 50 of the participants' mirgaines, 49 migraines decreased in severity and 36 were stopped when using AVE.
Another clinical study showed declines in depression, anxiety and suicidal ideation following a treatment program using AVE. A study by Berg and Siever used audio-visual entrainment devices on women suffering with seasonal affective disorder. Both depression and anxiety symptoms were reduced in participants, as compared to a placebo phase. Participants also reported improvements in their social lives, with increased happiness and sociability, decreased appetite, increased energy and weight loss. A study by Cantor and Stevens found significant decreases in depression scores in participants after 4 weeks of using AVE.
A study by Thomas and Siever showed that many people with chronic temporo-mandibular dysfunction (TMD) brace up when asked to relax. AVE at 10 Hz produced deep masseter muscle relaxation and finger warming within six minutes. Audio entrainment has shown promise as a singular therapeutic modality for treating jaw tension and TMD pain. AVE has been used to reduce jaw pain, patient anxiety and heart rate during dental procedures.
Pulse (signal processing)
In signal processing, the term pulse has the following meanings:#A rapid, transient change in the amplitude of a signal from a baseline value to a higher or lower value, followed by a rapid return to the baseline value....
of tones
Note
In music, the term note has two primary meanings:#A sign used in musical notation to represent the relative duration and pitch of a sound;#A pitched sound itself....
to guide the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
into various states of brainwave activity. AVE devices are often termed light and sound machines or mind machines. Altering brainwave activity is believed to aid in the treatment of psychological and physiological disorders
Disease
A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...
.
Introduction
All of our senses (except smell) access the brain's cerebral cortexCerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
via the thalamus
Thalamus
The thalamus is a midline paired symmetrical structure within the brains of vertebrates, including humans. It is situated between the cerebral cortex and midbrain, both in terms of location and neurological connections...
, and because the thalamus is highly innervated with the cortex, sensory stimulation can easily influence cortical activity. In order to affect brain (neuronal) activity, sensory stimulation must be within the frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
range of roughly 0.5 to 25 hertz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
(Hz). Touch, photic and auditory stimulation are capable of affecting brain wave activity. A large area of skin must be stimulated to affect brainwaves, which leaves both auditory and photic stimulation as the most effective and easiest means of affecting brain activity. Therefore, mind machines are typically in the form of light and sound devices.
Auditory or visual stimulation (AVS) can take a variety of forms, generating different subjective and clinical effects. The simplest form of stimulation is to present a series of random light flashes and/or sound pulses to a subject, such as from watching TV or cars drive by, and investigate the resulting subjective experiences or electroencephalography
Electroencephalography
Electroencephalography is the recording of electrical activity along the scalp. EEG measures voltage fluctuations resulting from ionic current flows within the neurons of the brain...
(EEG) effects. AVE, however, involves organized, repetitive stimulation at a particular frequency for a specific period of time, and the frequency of stimulation is reflected within the EEG. This is called "open loop" stimulation, or free-running entrainment, and is not contingent on monitoring brainwaves in any way. "Close loop" AVE would involve visual and auditory stimulation in response to one's EEG.
History
Clinical reports of flicker stimulation appear as far back as the beginning of the 20th century. Pierre JanetPierre Janet
Pierre Marie Félix Janet was a pioneering French psychologist, philosopher and psychotherapist in the field of dissociation and traumatic memory....
, at the Salpêtrière Hospital
Pitié-Salpêtrière Hospital
The Pitié-Salpêtrière Hospital is a teaching hospital located in Paris, France. Part of the Assistance publique - Hôpitaux de Paris, it is one of Europe's largest hospitals...
in France, reported that by having his patients gaze into the flickering light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
produced from a spinning, spoked wheel in front of a kerosene lantern, they showed a reduction in their anxiety
Anxiety
Anxiety is a psychological and physiological state characterized by somatic, emotional, cognitive, and behavioral components. The root meaning of the word anxiety is 'to vex or trouble'; in either presence or absence of psychological stress, anxiety can create feelings of fear, worry, uneasiness,...
and hysteria
Hysteria
Hysteria, in its colloquial use, describes unmanageable emotional excesses. People who are "hysterical" often lose self-control due to an overwhelming fear that may be caused by multiple events in one's past that involved some sort of severe conflict; the fear can be centered on a body part, or,...
. With the development of the EEG, Adrian and Matthews published their results showing that the alpha rhythm could be "driven" above and below the natural frequency with photic stimulation. This discovery prompted several small physiological outcome studies on the "flicker-following response," the brain's electrical response to repetitive stimulation As EEG equipment improved, so did a renewed interest in the brain's evoked response to photic and auditory entrainment and soon, a variety of studies were completed.
In 1956, W. Gray Walter published the first results on thousands of test subjects comparing flicker stimulation with the subjective emotional feelings it produced. Test subjects reported all types of visual illusions and in particular, the "whirling spiral" which was significant with alpha production. In the late 1950s, as a result of Kroger's observations as to why US military radar operators often drifted into trance
Trance
Trance denotes a variety of processes, ecstasy, techniques, modalities and states of mind, awareness and consciousness. Trance states may occur involuntarily and unbidden.The term trance may be associated with meditation, magic, flow, and prayer...
, Kroger teamed up with Sidney Schneider of the Schneider Instrument Company. They produced the world's first electronic clinical photic stimulator - the Schneider Brain Wave Synchronizer. It had powerful hypnotic qualities and soon studies on hypnotic induction were published A variety of companies developing AVE (light and sound) devices have been established since this time.
Physiology of Audio-Visual Entrainment
AVE is believed to achieve its effects through several mechanisms simultaneously. These include:- altered EEG activity
- dissociation/hypnotic induction
- limbic stabilization
- improved neurotransmitter production
- altered cerebral blood flow
AVE consists of constant, repetitive stimuli of the proper frequency and sufficient strength to "excite" the thalamus and neocortex
Neocortex
The neocortex , also called the neopallium and isocortex , is a part of the brain of mammals. It is the outer layer of the cerebral hemispheres, and made up of six layers, labelled I to VI...
. These stimuli do not transfer energy directly into the cortex. The direct transmission of energy from AVE only goes so far as to excite retinal cells in the eyes and pressure sensitive cilia within the cochlea
Cochlea
The cochlea is the auditory portion of the inner ear. It is a spiral-shaped cavity in the bony labyrinth, making 2.5 turns around its axis, the modiolus....
in the ears
EARS
EARS may refer to:* Electoral software* Electronic Arts, Redwood Shores campus.* Emirates Amateur Radio Society...
. The nerve pathways from the eyes and ears carry the elicited electrical potentials into the thalamus. From there, the entrained electrical activity within the thalamus is "amplified" and distributed throughout other limbic areas and the cerebral cortexes via the cortical thalamic loop. AVE involves the continuous electrical response of the brain in relation to the stimulus frequency plus the mathematical representation (harmonics) of the stimulus wave shape.
Effects of Audio-Visual Entrainment
AVE effects on the EEG are found primarily over the sensory-motor strip, frontally, and in the parietal lobeParietal lobe
The parietal lobe is a part of the Brain positioned above the occipital lobe and behind the frontal lobe.The parietal lobe integrates sensory information from different modalities, particularly determining spatial sense and navigation. For example, it comprises somatosensory cortex and the...
(somatosensory) regions and slightly less within the prefrontal cortex.
It is within these areas where motor activation, attention
Attention
Attention is the cognitive process of paying attention to one aspect of the environment while ignoring others. Attention is one of the most intensely studied topics within psychology and cognitive neuroscience....
, executive function, and somatosensory (body) awareness is primarily mediated. Auditory entrainment (AE) is the same concept as visual entrainment, with the exception that auditory signals are passed from the cochlea of the ears into the thalamus via the medial geniculate nucleus
Medial geniculate nucleus
The Medial Geniculate Nucleus or Medial Geniculate Body is part of the auditory thalamus and represents the thalamic relay between the inferior colliculus and the auditory cortex...
, whereas visual entrainment passes from the retina into the thalamus via the lateral geniculate nucleus
Lateral geniculate nucleus
The lateral geniculate nucleus is the primary relay center for visual information received from the retina of the eye. The LGN is found inside the thalamus of the brain....
. Eyes-closed AVE at 18.5 Hz has been shown to increase EEG brainwave activity by 49% at the vertex. At the vertex (with the eyes closed) AE has been shown to increase EEG brainwave activity by 21%. Successful entrainment leads to a meditative, peaceful kind of dissociation, where the individual experiences a loss of somatic and cognitive awareness. However, it is possible for visual entrainment to trigger seizures.
Evidence of Sensory Effects of AVE
Both Huxley and Walter were among the first to articulate the subjective correlates of photic stimulation. They described subjective experiences of incessantly changing patterns, whose color was a function of the rate of flashing. Between ten and fifteen flashes per second, Walter reported orange and red; above fifteen, green and blue; above eighteen, white and grey. Huxley also described enriched and intensified experiences when subjects were under the effects of mescalineMescaline
Mescaline or 3,4,5-trimethoxyphenethylamine is a naturally occurring psychedelic alkaloid of the phenethylamine class used mainly as an entheogen....
or lysergic acid
Lysergic acid
Lysergic acid, also known as D-lysergic acid and -lysergic acid, is a precursor for a wide range of ergoline alkaloids that are produced by the ergot fungus and some plants. Amides of lysergic acid, lysergamides, are widely used as pharmaceuticals and as psychedelic drugs...
. In his view, the rhythms of the lamp interacted with the rhythms of the brain's electrical activity to produce a complex interference pattern, which is translated by the brain's perceptual circuits into a conscious pattern of color
Color
Color or colour is the visual perceptual property corresponding in humans to the categories called red, green, blue and others. Color derives from the spectrum of light interacting in the eye with the spectral sensitivities of the light receptors...
and movement
Movement
-In society and the arts:* Social movement, a coordinated group action focused on a political or social issue* Political movement, a coordinated group action focused on a political issue* Art movement, a tendency or style in art followed by a group of artists...
. Glicksohn also reported on altered states of consciousness from photic driving and its relationship of self-perceived creativity.
Other studies have shown that stimulation can produce both transient and lasting changes in the EEG. Collura
Thomas F. Collura
Dr. Thomas F. Collura, Ph.D., PE it is the president of BrainMaster Technologies, Incorporated located in Bedford, Ohio and is the current president of the International Society for Neurofeedback & Research . He also has served the Association for Applied Psychophysiology and Biofeedback as the...
articulated the relationship between the low-frequency and high-frequency components of the steady-state visual evoked potential as reflecting anatomically and physiologically distinct response mechanisms.
Additional clinical studies explored the use of photic entrainment to induce hypnotic trance, to augment anasthesia during surgery, and to reduce pain, control gagging and accelerate healing in dentistry
Dentistry
Dentistry is the branch of medicine that is involved in the study, diagnosis, prevention, and treatment of diseases, disorders and conditions of the oral cavity, maxillofacial area and the adjacent and associated structures and their impact on the human body. Dentistry is widely considered...
. More recently, the induction of dissociation
Dissociation
Dissociation is an altered state of consciousness characterized by partial or complete disruption of the normal integration of a person’s normal conscious or psychological functioning. Dissociation is most commonly experienced as a subjective perception of one's consciousness being detached from...
was explored, which aided the understanding of dissociative pathology and development of better techniques for relaxing people suffering from trauma and posttraumatic stress disorder.
Dissociation begins after approximately four to eight minutes from properly applied AVE. A restabilization effect occurs where muscles relax, electro-dermal activity decreases, peripheral blood flow stabilizes, breathing becomes diaphragmatic and relaxed, and heart rates becomes uniform and smooth. Visual entrainment alone, in the alpha frequency range (7–10 Hz), has been shown to easily induce hypnosis, and it has been shown that nearly 80% of subjects entered into either a light or deep hypnotic trance within six minutes during alpha AVE. AVE provides an excellent medium for achieving an altered state of consciousness.
Treatment Implications of AVE
A review of 20 studies on brainwave entrainment found that it is effective in improving cognition and behavioral problems, and alleviating stress and pain.The results of a study on children with attention-deficit disorder found that AVE was more effective than neurofeedback for treating ADD symptoms.
A migraine headache study involving seven migraine sufferers found that AVE sessions reduced migraine duration from a pretreatment average of 6 hours to a posttreatment average of 35 minutes. Measuring 50 of the participants' mirgaines, 49 migraines decreased in severity and 36 were stopped when using AVE.
Another clinical study showed declines in depression, anxiety and suicidal ideation following a treatment program using AVE. A study by Berg and Siever used audio-visual entrainment devices on women suffering with seasonal affective disorder. Both depression and anxiety symptoms were reduced in participants, as compared to a placebo phase. Participants also reported improvements in their social lives, with increased happiness and sociability, decreased appetite, increased energy and weight loss. A study by Cantor and Stevens found significant decreases in depression scores in participants after 4 weeks of using AVE.
A study by Thomas and Siever showed that many people with chronic temporo-mandibular dysfunction (TMD) brace up when asked to relax. AVE at 10 Hz produced deep masseter muscle relaxation and finger warming within six minutes. Audio entrainment has shown promise as a singular therapeutic modality for treating jaw tension and TMD pain. AVE has been used to reduce jaw pain, patient anxiety and heart rate during dental procedures.