The use of Auditory Beat Stimulation (ABS) such as binaural, monaural and isochronic beats falls into the field of study called psychoacoustics. The research conducted so far, although not conclusive, has provided evidence that the effects of ABS can be registered in the brain. Some say that the response evoked in the brain (or brainwave entrainment) does not have a real effect on emotional and psychological states whereas others have observed significant results. As with any other field of research, the more experiments will be conducted under rigorous conditions, the more we will understand the effects of ABS. However, there is already enough evidence that ABS, also combined with music, can influence states such as stress and anxiety.
Psychoacoustics is the study of the perception of sound and the responses of the brain to the stimuli of sound waves.
Brainwave Entrainment refers to the brain’s electrical response to rhythmic sensory stimulation, such as pulses of sound or light.
Every cell in the brain produces electricity as a byproduct of its activity. The sum of all the electrical charges creates patterns in the brain and these patterns are related to brain waves activity.
The brain waves (measured in Hertz, or cycles per second) have been categorised by different spectrums. While it is still officially debated whether different brain wave patterns are associated with different psychological and physiological states, there is a common acceptance of these relationships:
- Gamma above 38-42Hz: heightened perception
- Beta 12 Hz to 38 Hz: arousal, alertness and some drug effects
- Alpha 8 Hz to 12 Hz: physical and mental relaxation; meditation, sedation and relaxed but focused activities (sports, watching TV)
- Theta 3 Hz to 8 Hz: deep meditation; hypnosis; dreaming; REM sleep
- Delta 0.5 Hz to 3 Hz: deep sleep, general anaesthesia
- Infra-Low below 0.5 Hz: very little known at the moment
When the brain is given a stimulus, through the ears, eyes or other senses, it emits an electrical charge in response, called a Cortical Evoked Response. This activity can be measured using sensitive electrodes attached to the scalp.
When the brain is presented with a rhythmic stimulus, such as a drum beat, for example, the rhythm is reproduced in the brain in the form of these electrical impulses. If the rhythm becomes fast and consistent enough, it can start to resemble the natural patterns of the brainwaves activity. When this happens, the brain responds by synchronising its own electric cycles to the external rhythm. This is commonly called the Frequency Following Response (or FFR).
One of the most popular ways of producing brainwave entrainment is the use of “Binaural Beats”, auditory phenomena that occur within the brain. When we send a separate and distinct tone to each ear, the brain perceives the difference between the frequencies of the two tones as a third “phantom” tone. What happens is that the brain detects a phase difference and experiences it as a “beat”. Let’s say we send a tone with a frequency of 200 Hz to one ear and on of 208 Hz to the other, the brain will produce a pulse equal to the difference of the two tones, in this case 8 Hz.
Binaural beats are most effective when listened to through headphones, making use of the brain’s ability to create an illusory spatial image from stereophonic sound, also called “binaural field”.
However, Binaural Beats, although very popular, are not the most effective way of creating entrainment. Their true potential resides in eliciting hemispheres synchronisation due to the fact that the creation of the beats happens inside the brain.
The systems that are believed to be involved in the effects of binaural beats and altered states of consciousness are:
- The Superior Olivary Nucleus, located in the medulla oblongata. This is where the nerve impulses from each ear are first received.
- Reticular Activating System (RAS), a large net-like region in the brain stem which plays a major role in filtering sensory input and focusing attention and awareness and is strongly involved in the cortical processing of binaural beats located in the brainstem. It helps maintain homeostasis or internal stability. Complex, brain-wave-like patterns such as the ones resulting from binaural beats can be recognized by the RAS as brain-wave patterns information. Provided this information is not met by internal or subconscious conflicts, the RAS will alter states of consciousness to match the incoming stimulus as a natural function of maintaining homeostasis.
- The RAS connects with the Extended Reticular Thalamic Activation System (ERTAS) and might be considered the most important system in the application of binaural beats frequencies. This system is most commonly known to connect with emotion, attention, wakefulness and sleep.
Besides binaural beats, there are other, less popular but more effective methods of ABS, namely monaural beats, where the two different tones are blended before reaching the ears, making the use of headphones not necessary (unless preferred) and isochronic tones, where a given tone is repeated at regular intervals with silence in between.
Especially with isochronic tones, what causes a more effective entrainment is the amplitude modulation that can reach 50 dB, which is a lot greater than with binaural beats.
What’s the difference between Isochronic Tones and Binaural Beats?
Isochronic tones are more effective in entraining the brainwaves to the desired frequency whereas Binaural beats have the additional effect of stimulating hemisphere synchronisation.
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Sources and research:
The Impact of Monaural Beat Stimulation on Anxiety and Cognition – Leila Chaieb, Elke C. Wilpert, Christian Hoppe, Nikolai Axmacher and Juergen Fell
Cortical Evoked Potentials to an Auditory Illusion: Binaural Beats – Hillel Pratt, Arnold Starr, Henry J. Michalewski, Andrew Dimitrijevic, Naomi Bleich, and Nomi Mittelman
Neuromagnetic Responses to Binaural Beat in Human Cerebral Cortex – Shotaro Karino, Masato Yumoto, Kenji Itoh, Akira Uno, Keiko Yamakawa, Sotaro Sekimoto, and Kimitaka Kaga
Intracranial electroencephalography power and phase synchronization changes during monaural and binaural beat stimulation – Ann-Katrin Becher, Marlene Höhne, Nikolai Axmacher, Leila Chaieb, Christian E. Elger and Juergen Fell
A prospective, randomised, controlled study examining binaural beat audio and pre-operative anxiety in patients undergoing general anaesthesia for day case surgery – R. Padmanabhan, A. J. Hildreth and D. Laws
Original sound compositions reduce anxiety in emergency department patients: a randomised controlled trial – Tracey J Weiland, George A Jelinek, Keely E Macarow, Philip Samartzis, David M Brown, Elizabeth M Grierson, Craig Winter
Auditory beat stimulation and its effects on cognition and mood states – Leila Chaieb, Elke Caroline Wilpert, Thomas P. Reber and Juergen Fell
The impact of binaural beats on creativity – Susan A. Reedijk, Anne Bolders and Bernhard Hommel
Brain Responses to a 6-Hz Binaural Beat: Effects on General Theta Rhythm and Frontal Midline Theta Activity – Nantawachara Jirakittayakorn and Yodchanan Wongsawat