Tzu-Yuan Yen, MD
Dreams are any mental activities during sleep. Contents of dream, such as perceptions, bodily feelings, and thoughts, may be forgotten by dreamers after awake. We do not always remember our dreams. Some insist that they never dream, but when they were waken by others at different sleep stages, they might found that they do dream. Research findings shows that only about 2% people seldom dream.
So why we dream? Given patterns of mental activities might have its advantages during evolution, dreams as well may possess some niche for human race. The NEXTUP (Network EXploration To Understanding Possibilities) Model is a theory explaining cognitive function of dream. According to this model, memories of daily salient events were processed during sleep. Memory formation is a process of making connections. In dreams, episodic memories with strong relevance connect with salient event in N1 stage. Those with weak relevance connect with salient events in N2 stage. Finally, semantic memory connect to salient event in REM (rapid eye movement) stage. After we wake up, often we have different point of view toward recent concerns.
Two neurotransmitters play important rule in memory processing during dreams. Noradrenaline can label salience to mental objects. During N2 and REM sleep, decreasing level or complete absence of Noradrenaline foster formation of weak associations. Decreased level and complete absence of serotonin during N2 and REM sleep help render these weak associations meaningful. So dream content not only feels strange (because they are weak associations), but also feels important. Memory processing of dreams help us see thing in a new light, which might help solve problems with its illogical, seemingly absurd associations.
Reference:
- When Brains Dream. Antonio Zadra, Robert Stickgold. 2021. Norton.