Duke University has a good article on the latest research into the brain’s internal time keeping.
"…the brain’s most important, and mysterious, clocks — the one governing timing intervals in the seconds to minutes range. Such interval timing occupies the middle neurological ground between two other clocks — the circadian clock that operates over the 24-hour light-dark cycle, and the millisecond clock that is crucial for such functions as motor control and speech generation and recognition. Meck is a professor and Buhusi is an assistant research professor in the Department of Psychological and Brain Sciences.
Interval timing is central to broader coordination of tasks such as walking, manipulating objects, carrying on a conversation and tracking objects in the environment, they said".
This natural rhythm is thought to be poor in people with ADHD and Dyslexia. See Rhythm and Dyslexia, Interactive Metronome with the Bramhall NDT Practice, Interactive Metronome Research and Music.