Possibly related to "brainwave entrainment". > Brainwave entrainment, also referred to as brainwave synchronization and neural entrainment, refers to the hypot

Possibly related to "brainwave entrainment". > Brainwave entrainment, also referred to as brainwave synchronization and neural entrainment, refers to the hypothesized capacity of the brain to naturally synchronize its brainwave frequencies with the rhythm of periodic external stimuli, most commonly auditory, visual, or tactile. > It is believed that patterns of neural firing, measured in Hz, correspond with states of alertness such as focused attention, deep sleep, etc. It is hypothesized that by listening to these beats of certain frequencies one can induce a desired state of consciousness. https://en.wikipedia.org/wiki/Brainwave_entrainment https://en.wikipedia.org/wiki/Brainwave_entrainment