Which part of brain controls transition between sleeping and wakefulness?

Explanation

The pons contains the centres that switch the brain between sleep and wakefulness and it also regulates the rhythm of breathing alongside the medulla. The medulla is the tempting answer because it too is part of the brain stem, but its role is the automatic control of heart rate, breathing and blood vessel diameter. The cerebellum handles balance and coordination and takes no part in the sleep cycle.