It is still not clear why we dream at night, but scientists have made strides in understanding the nature of dreams in recent years. Dreams are influenced by what happens to us during the day. Some of the information we gather during the day is kept, and some discarded to clear out our mental storage space. To achieve this, our brains need some down time to disconnect.
Our brains are able to divide our nights into two types of sleep: slow wave sleep (SWS) and rapid-eye movement (REM) sleep. During SWS, the brain’s hippocampus essentially plays movies to our frontal cortex that are essentially condensed packets of information, playing at 10x speed. These dreams tend to be static, involving old memories, and are emotional. Nightmares, bedwetting, sleep-walking, and night terrors occur during this stage.
The transition to REM sleep occurs when our hippocampus is shut down to allow our frontal cortex to process this bombardment of information. This is experienced as narrative dreams that feel real, as if occurring in real time. During REM sleep, our brain is filtering out useless memories in favor of useful ones. Memories with strong emotional weight are the long-lasting ones.
Setting aside a high enough volume of sleep is important in allowing an adequate duration of both SWS and REM sleep to take place. This helps process the day’s information intake during your down time, and retain important memories for future use. This is why the sleep deprived often have issues with memory recall.