Have you ever experienced a feeling of extreme peace and tranquility when you are looking at the flickering flames in a wooden fire place or felt at peace when driving on a road early in the morning as the sunlight and the shadows of the tress lining the streets alternate in an almost rhythmic pattern? What is essentially happening in both these instances is that the brain is being presented with a visual stimulus at a certain frequency repeatedly, and the brain has a strong tendency to mimic this frequency in its electric impulses.
This characteristic trait of the brain is called Frequency Following Response or FFR.
This property of the brain is successfully exploited in brainwave entrainment to produce a specific mental or physical state.
To make the principle simple, let's take a look at how our brain works.
The brain interprets the various stimuli that it receives from the sensory organs in the form of electrical impulses; the response generated to these stimuli is also in the form of impulses.
These electrical impulses follow set frequencies which dictate our moods and actions.
Usually these frequencies change naturally, however if you could change them with the help of an external stimulus it would give you greater control over what and how you feel; this is the principle used in brainwave entrainment Sound pulses like Isochronic tones and Binaural beats are used to guide the brain to a specific frequency that is associated with a particular mental or physical state.
The five frequencies that are used to achieve these various states are Beat, Alpha, Theta, Delta and gamma.
Each frequency range corresponds to a particular state of mind, emotion and physical state.
For instance Beta brainwaves are associated with normal consciousness; they are present when we are wide awake and alert or processing and analyzing information.
They are also associated with stress.
Alpha brainwaves on the other hand correspond to a state of deep relaxation, the kind that can be achieved through meditation.
While Theta waves are associated with sleep and deep meditation; the Delta brainwaves are the slowest and they are present when we are sleeping very deeply or unconscious.
There is very little information available about the gamma waves except for the fact that they are the fastest.
In brainwave entrainment devices that produce either sound or visual stimulus are used to align the brains internal frequency with the frequency of the stimuli.
So if you want to achieve a state of relaxation you would want to go for alpha frequency while people looking deep sleep should opt for theta frequency range.
In simpler words you are coaxing your brainwaves into a frequency that is associated with a feeling that you desire.