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Isochronic tones are regular beats of a single tone that are used alongside monaural beats and binaural beats in the process called brainwave entrainment. At its simplest level, an isochronic tone is a tone that is being turned on and off rapidly. They create sharp, distinctive pulses of sound. The volume or intensity of the sound goes almost directly from 0 to 100 and back again in an evenly-spaced manner. They differ from monaural beats, which are constant sine wave pulses rather than entirely separate pulses of a single tone. Additionally, isochronic tones differ from binaural beats in that they use a single tone, not two. Isochronic tones are usually incorporated or disguised with music, as the undisguised tones can be unpleasant.
It is possible, through external stimulation (like strobe-lights and aural frequencies), to induce a synchronised rhythm in the “brain waves” that is not the normal state of these waves. Brain waves in this context refers to the electrical and magnetic current emitted by your neurons when they communicate. The rapid, regular pulses of light emitted by a strobe light, or in some videos, can cause irregular neural impulses and this leads to an epileptic fit, due to a phenomenon known as photic driving. This is a common form of brainwave entrainment.
Brainwave entrainment does not have a long-term effect on the patterns of neural impulses. That is, very soon after the external stimulus stops the brainwaves return to their normal state. In fact, there is some evidence that brain waves are evenly spaced on a logarithmic scale to prevent entrainment and cross talk. In a paper by G. Karl Steinke and Roberto F. Galán  the authors show, by mathematical modelling, that the complexity of these signals is a good indicator of brain fitness. They show that virtual brains modelling diseased states show lower complexity than those modelling healthy states.
Clinical Neurologist Dr. Steven Novella has published an article on brainwave entrainment, saying; 'A number of companies and individuals have then extrapolated from the phenomenon of entrainment to claim that altering the brain waves changes the actual functioning of the brain. There is no theoretical or empirical basis for this, however.'  Brainwave entrainment has been claimed to assist with Cognition, Stress Reduction and AD-HD Disorder. While there have been many small-scale studies done, there has not yet been a large-scale or long-term study of brainwave entrainment.
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