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Binaural beats

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Binaural beats or binaural tones are low-frequency pulsations in the perceived loudness of a sound when two tones at slightly different frequencies are played separately, one into each of the subject's ears, using binaural headphones. The frequency of the tones must be below about 1,000 to 1,500 hertz. The difference between the two frequencies must be small (approximately below 30 Hz), otherwise you will not hear a beating, but two distinct sounds and you will be able to say in which ear is the basser and in which is the trebler. The effect was discovered in 1839 by Heinrich Wilhelm Dove.

Interest in binaural beats can be classified into two categories. First, they are of interest to neurophysiologists investigating the sense of hearing. Second, there are those who believe that binaural beats may influence the brain in more subtle ways, producing relaxation and other health benefits.

Physiology

The sensation of binaural beats is believed to originate in the superior olivary nucleus, a part of the brainstem. They appear to be related to the brain's ability to locate the sources of sounds in three dimensions.

Hypothetical effects on brain function

Overview

Some people believe that binaural beats can influence functions of the brain besides those related to hearing. This belief appears to be based on the coincidence between the range of beat frequencies that can be achieved, and the frequencies of the signals observed in electroencephalograms (EEGs).

According to this view, when the perceived beat frequency corresponds to the delta, theta, alpha or beta range of brainwave frequencies, this causes the brainwaves to entrain to or move towards the beat frequency. For example, if a 315 Hz sine wave is played into the right ear and a 325 Hz one into the left ear, the brain is supposed to be entrained towards the beat frequency (10 Hz, in the alpha range). Since alpha range is usually associated with relaxation, it is supposed to have a relaxing effect.

Brain waves

Main article: Electroencephalography
Frequency range Name Usually associated with:
>40 Hz Gamma waves  
13-40 Hz Beta waves Attention
7-13 Hz Alpha waves Relaxation (while staying awake)
4-7 Hz Theta waves Dreams, deep meditation
<4 Hz Delta waves Deep dreamless sleep

(the precise boundaries between ranges vary among definitions, and there is no universally accepted standard)

The dominant frequency determines your current state. For example, if your alpha waves dominate, you are in the alpha state (this happens when you are relaxed but awake). However, also other frequencies will be present, albeit with smaller amplitudes. Gamma waves aren't usually your dominant frequencies.

The brain entraining is more effective if the entraining frequency is close to your current dominant frequency. Therefore, it is suggested to start with a frequency near to your current dominant frequency (if you're awake it is likely to be about 20 Hz or little less), and then slowly decreasing it towards the desired frequency.

To some people, pure sine waves are unpleasant, therefore a pink noise or another background (e.g. natural sounds such as river noises) can also be mixed with them. In addition to that, as long as the beat is audible, increasing the volume won't improve the effectiveness, therefore using a low volume is usually suggested. Some people say that the volume should be so low that the beating should not even be clearly audible, but this does not seem to be the case (see the next paragraph).

It should be made clear that binaural beats are not magic: just passively listening to binaural beats does not necessarily alter your state of consciousness. An active mental participation by the subject is needed to produce the synchronization. Experiments in which beats were not audible [1] (e. g. with a background pink noise 15 dB louder than the sine waves) have failed to report any effect. Therefore it is also possible that the effect of binaural beats is due to placebo. However, to prove this one would have to make people believe to listen to binaural beats without really listening to them, which is only possible if the subject cannot distingiush between binaural beats and non-binaurals. On the other hand, it is possible to examinate the EEG of a person before and after a binaural beat session to check whether the relaxing effect is merely subjective or there really is a change in the EEG. Nevertheless, it seems that no objective, serious, extensive research has been done into that.

Other uses

In addition to lower the brain frequency to relax the listener (or to raise it to help focusing), there are other controversial, alleged uses for binaural beats. For example, some say that using specific frequencies you can stimulate certain glands to produce desired hormones, sometimes even relating them with chakras. This is highly disputed, and even among people who consider this possible many agree that the precise frequencies may vary from person to person.

Among other alleged uses, there are reducing learning time and sleeping needs (theta waves are thought to improve learning, since children, who have stronger theta waves, usually learn faster than adults; and some people find that half an hour in the theta state can reduce sleeping needs up to four hours; however, this is supposed to happen with any way to get into theta state, e.g. meditation); some use them for lucid dreaming and even for achieving out-of-body experiences, astral projection, telepathy and psychokinesis. However, most people believe that these phenomena (except lucid dreams, which are acknowledged even by mainstream science) do not exist, let alone that they can be achieved by training the brain to a specific frequency.

They have been also experimented for the treatment of addictions, and for recovery of repressed memories, but like any other way to do that this can bring to false memories.

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