During REM (randomized eye movement) sleep, rapid eye movement occurs and we dream during this phase. The duration of REM sleep is about 20% of the total sleep and there are total 5 REM periods in each sleep.
The peripheral area extends to the mesencephalic-pontine reticular formation (MPRF). Which in association with the neocortex and spinal cord is responsible for producing events associated with the REM sleep.
Thus, the blank can be filled with REM sleep.