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Since ancient times many cultures and traditions have used sound in practices aimed to alter the emotional and physical state of the individual. We find some examples in Tibetan chants, Gregorian chants, shamanic drumming and in the use of mantra in meditation.

Within the frame of the current scientific method, the science that studies the perception of sound and its influence on our psyche is known with the name of psychoacoustics.

One of the phenomena studied by psychoacoustics is the ability of our brain to “entrain” with the frequency of external impulses. What gets synchronised during this process is the brainwaves’ frequency which means the frequency at which the neurons exchange information between themselves.

We can measure brainwaves’ frequency with an electroencephalogram (EEG), a technique that measures the electrical activity of our nervous system through electrodes placed on the scalp.

Our brainwaves change according to what we are doing and feeling. When low frequencies predominate we feel tired, slow or dreamy. When the frequencies are higher we feel more active and vigilant.

Brainwaves frequencies are subdivided in categories according to their function and are measured in Hertz (cycle per second):


These are lowest frequencies and because of this they are more difficult to measure and study. Very little is known about this kind of waves. They seem to play an important role in the networking processes of our brain.

DELTA WAVES (0.5 to 4 Hz)

Delta waves are detected during deep sleep and in the deepest states of meditation. Delta waves suspend the perception of the external world and aid healing processes. 

THETA WAVES (4 to 8 Hz)

Theta waves are associated with sleep and meditation. While in this state we interact with our inner world made of dreams, visions, memories and intuitions. Theta state is the territory in which we store our fears and create our imaginary world. Daydreaming and creative activities are connected to this kind of brainwaves.

ALPHA WAVES (8 to 12 Hz)

Alpha waves occur in the resting state of the brain. These waves take place during the quiet flow of thoughts and in some light states of meditation.

BETA WAVES (13 to 30 Hz)

Beta waves are dominant in the normal waking state, when our attention is directed outwards, solving problems, judging or taking decisions. It signals fast brain activity and a state of alert.

GAMMA WAVES (30 to 70Hz)

Gamma waves are the fastest of brainwaves and indicates a fast exchange of information between different areas of the brain. As the frequency of Gamma brainwaves is higher than the frequency of neuronal firing, it is still unknown how these frequencies are generated. In the beginning Gamma waves were dismissed as spare “brain noise” until when they have been detected during states of altruism, universal love and other states focused on a feeling of expansion towards the totality.

BrainWave Entrainment

Like our heartbeat and respiration, our nervous system too is a precious link to our emotional and physical state. From our cellular activity to the work of our organs we are a complex orchestration of rhythms, aimed to play as an harmonious state of well-being, or as a disturbed noise when we break the balance between the parts. We can draw many different cause-effect schemes to  connect our rhythms, but actually we work as a holistic being. Each part of the totality affects and is affected by any other part.

Brainwaves Entrainment (BWE) uses rhythmic impulses to alter brainwaves frequencies, and with them the state of the mind. By using rhythmic impulses we can encourage our brain to sync its dominant frequency to the rhythm of the chosen impulse.

 The kind of impulses that are used generally are optical and auditory impulses. In the former case light beams are flashed on the (closed) eyes of the patient, at the desired frequency. In the case of auditory impulses the phase, the frequency and the amplitude of the sound-wave create the conditions for the brain to be shifted to the desired frequency.

The 3 most common forms of acoustic entrainment are isochronic tones, monaural beats and binaural beats.

Monaural beats

In physics and in acoustic a beat is the interference frequency resulting from the overlapping of two waves (generally sine waves) having slightly different frequencies.

If, for example, we overlap a 205Hz sound-wave with a 200Hz sound-wave, we obtain a third frequency equal to the difference between the first two (in this instance 205-200 = 5 Hz).

We can experiment this phenomenon by striking 2 tuning forks next to each other or during the tuning of musical instruments. 

The beating effect wanes as the difference between the two frequencies gets bigger, generally disappearing beyond 30Hz. After that threshold we start to hear the two frequencies as two distinct voices.

This kind of beats are called monaural because they can be generated by a single sound source, and can be perceived even by a single ear, unlike binaural beats.

Binaural beats

Binaural beats are generated playing two tones of slightly different frequency, one on each ear.

Binaural beats need two distinct sound-sources and both our ears to be produced and perceived. Because of this it’s advised to use circumaural headphones (headphones that cover the whole ear) rather than speakers or earbuds, to receive the impulse clearly and correctly.

Binaural beats are generated from the brain itself which overlaps the two frequencies, detects the difference of phase between the sound-waves and creates the illusory perception of a third frequency (the beat), equal to the difference between the first two. If we listen to a 347.5 Hz tone with our left ear and a 340 Hz tone with our right ear, we will hear a third frequency of 7.5 Hz, entirely produced by ourself.

 As for monaural beats, the bigger the difference in frequency between the two frequency, the fainter the beating effect becomes, until it completely disappear when it approaches 30 Hz.

Isochronic tones

Isochronic tones are pulsed tones, that means tones interrupted by gaps of silence, equally repeated at a given frequency. Unlike monaural and binaural beats, where the frequencies overlapping creates a soft pulse, in isochronic tones it is the amplitude (the volume) to be rapidly modulated, creating evenly spaced pulses that are easily perceived, thanks to the complete silence between a pulse and the next one.

Mind tweaking ?

The first known clinical application of BrainWave Entrainment is attributed to Pierre Janet. In the late 1800s Janet noted improvements in patients that suffered from hysteria, anger and depression when they were asked to gaze into the flickering light of a spoked wheel placed in front of a lantern. Passing through the splits of the rotating wheel, the light created a strobe effect, responsible of the change detected in the patients. From Janet’s finding propagated a long series of studies on the effect of flickering light, followed by studies on optical and tactile entrainment, and on test subjects comparing flicker stimulation with the subjective emotional feelings it produced.

The development of BWE tools proliferated after the 1973 article by biophysicist Gerald Oster, Auditory Beats in the Brain. In his article Oster describes the effect of binaural beats and suggests to use the way these beats are perceived as a diagnostic tool.

Brainwaves have been associated with any kind of emotional and neurological condition. Any change in our perception is translated into a change of our brainwaves. Excessive activity on some frequency bands has been associated with depression, anxiety, insomnia, nightmares, aggression, anger. An activity below the standard values is linked to attention deficit, sleep problems, chronic pain.

Brainwaves entrainment is used to trigger different state of consciousness such as: trance, meditation, cognitive attention, relaxation, sleep.

A word of caution

Although the frequency bands described above  (delta, alpha, beta etc..)  are useful to spot the area of interest we want to work with, they give us an over-simplistic view of what actually happens. Our brain never works on a singular frequency at a time, but has a wide variety of frequencies working together with peaks on certain areas. It is possible to be in REM sleep and having activity in the alpha range, although the peak may be within the theta frequencies range.

For many who approach BWE, to work on brainwaves is a shortcut to access states of consciousness otherwise difficult to experience, which usually require a long training and discipline on various paths, like yoga or meditation. This is helping in making BWE more popular. Obviously such a work comes with its risks. For example, in 1997 a Japanese television broadcasted a cartoon which contained 5 seconds of flickering light. The episode provoked seizures to hundred of children who happened to be in from of the tv screen at that time (according to a national survey 618 children have suffered from vomit and convulsions after watching the cartoon). If an epileptic is exposed to a impulse that has the same frequency of the seizure, this will produce an epileptic attack.

Everyone is different, with its own needs and peculiarities, which makes it impossible to have a recipe or treatment that fits all.

Who wants to take advantage of scientific tool in order to understand if and what king of brainwave entrainment might be beneficial, can avail him/herself of instruments such as the EEG (electroencephalogram) and the QEEG (quantitative electroencephalogram). Another interesting diagnostic method is neurofeedback. Neurofeedback is the monitoring of neurological alterations aimed in training the patient to take control of those processes that once he/she was unaware of.

Such tools used together with brainwave entrainment are part of that new trend that goes by the name of bio-hacking.

I personally find inspiring the tendency to “hack” one’s own mind and body. This approach triggers the question “who hacks what?”, making the whole question take a quantum leap towards the realm of metaphysics, where the human being tries to get out of its own limits by experiencing oneself. 


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