Binaural Beats

Binaural beats are a form of  brainwave entrainment.

They cause two slightly different tones to be played into each ear. These tones are then combined in the brain itself, forming a beat that entrains the brain from the inside out.

One benefit is that in order for the brain to create a binaural beat, it must use both hemispheres of the brain (right and left), which can result in what is called "hemispheric synchronization". 

Binaural beat audios must be listened to with headphones.