People have a genetic sleep code called their chronotype, which dictates when their brain releases hormones like melatonin, cortisol, adrenaline, and dopamine.

A person's chronotype changes with age; babies are Lions, toddlers are Bears, adolescents become Wolves, and then it sets into one of the three or four types around age 23-24 for 25-30 years.

Melatonin is a hormone produced inside the body that tells the body when it is bedtime.

A 2020 study with nearly 800 students found a clear synchrony effect, where students performed significantly better when their class schedule matched their chronotype.

Sleep works in the brain through two separate systems: sleep drive and sleep rhythm.

Staying in sync with daylight by going to bed earlier and waking up closer to sunrise helps the brain regulate hormones like melatonin for sleep and cortisol for waking up.