The circadian rhythm is regulated by the suprachiasmatic nucleus (SCN), which dictates periods of activity during the day and inactivity at night.

“your Cadian rhythm is um you have a clock inside of your brain you have a central 24-hour clock and it's a master clock and that clock as you've spoken about many times is called the supermatic nucleus we don't have to get hung up on the the statement just think about it as your master 24-hour clock and it beats out this rhythmic sort of message of activity for us because we're dianal during the day and then inactivity at night activity during the day and it just goes up and down up and down every single day that's your Cadian Rhythm”