When our bodies shut down at night, our brains transport us into strange, convoluted alternate realities. Dreams range from the mundane to the fantastical, from classrooms to castles. Despite the sheer absurdity of many dreams, they always feel real. But where do dreams even come from, and why do we have them?
Definitions of a dream range from the generous “subjective experience during sleep” to the more specific “immersive spatiotemporal hallucination” (Siclari et al., 2020). Taken either way, dreams are characterized by increased blood flow to regions of the brain called the amygdala, hippocampus, and anterior cingulate cortex. The significant role that these regions play in regulating our emotions may explain the intense emotional aspect of many dreams (Schwartz & Maquet, 2002).
There are five stages of sleep. The first four stages are collectively categorized as non-Rapid Eye Movement, or NREM, sleep. Accordingly, the fifth stage is referred to as the REM stage. During REM sleep, our eyeballs flit back and forth underneath our eyelids, our muscles are paralyzed to prevent self-injury from dream enactment, and our brain activity reflects that of wakefulness (Siclari et al., 2020). Although dreams are more common in REM sleep, recent research has shown that shorter and less bizarre dreams occur during NREM sleep as well (Nielsen, 2000).
It seems like something as peculiar as dreaming should have a distinct purpose. However, the exact function of dreams is still unknown. One theory speculates that dreams are simply a byproduct of other brain activity, such as memory consolidation, that occurs during sleep. Sigmund Freud, oft-considered the father of psychology, believed that dreams allowed for the disguised fulfillment of the sexual and aggressive desires of the id. According to Freud, the id is the component of our personality that lies below our consciousness and drives primitive, aggressive desires. Other theories suggest that dreaming is evolutionarily advantageous because it allows us to practice behaviors important to our survival in our sleep, preparing us for the same events in wakefulness. These behaviors include hunting, mating, responding to threats, and socializing (Siclari et al., 2020).
Some people seem to remember their dreams every night, while others claim to never dream at all. Dream recall averages at about one dream a week, but this varies widely. Practices such as keeping a dream journal and setting an alarm during a period of likely REM sleep improve recall.
Recall is inherently easier with nightmares. By definition, nightmares cause awakening, while “bad dreams” contain similar emotionally troubling content but do not induce awakening (Robert & Zadra, 2014). There is evidence for a genetic predisposition to nightmares (Hublin et al., 1999).
Lucid dreams are a fascinating type of REM dreaming in which the individual is aware they are dreaming and may even be able to control the dream. Lucid dreams activate brain areas usually associated with insight and agency in wakefulness (Dresler et al., 2012). They also elicit the same eye movements and respiration patterns. For example, when asked to dive into a pool in their lucid dream, subjects briefly stopped breathing — as if they were underwater. The perception of time is also similar; counting from 0 to 10 in a lucid dream takes about as long as it does in real life. Lucid dreams provide particularly valuable insights into the mechanisms of dreaming because the dreamer can communicate with the researcher through pre-determined eye movements (Erlacher et al., 2014).
So what happens when we miss out on REM sleep and REM dreams? Unfortunately, modern society gives us plenty of chances to find out. Substances, especially alcohol and marijuana, decrease the time we spend in REM sleep. Medications such as benzodiazepines, antidepressants, and, ironically, sleeping pills also decrease REM sleep. Furthermore, exposure to artificial light before bed and the use of an alarm clock limit REM sleep. Collectively, the impact of these behaviors can hinder immune function, memory consolidation, and mood regulation (Naiman, 2017).
Despite everything that scientists have discovered about dreams, there is still much about them that remains a mystery. Recently, researchers have been trying to interpret the content of dreams by using brain scans and machine learning to decode certain patterns of brain activity (Horikawa et al., 2013). For now, however, we can only take what we do know and marvel at the rest. Every night brings its own all-expenses-paid adventure into another reality.
Dresler, M., Wehrle, R., Spoormaker, V. I., Koch, S. P., Holsboer, F., Steiger, A., Obrig, H., Sämann, P. G., & Czisch, M. (2012). Neural Correlates of Dream Lucidity Obtained from Contrasting Lucid versus Non-Lucid REM Sleep: A Combined EEG/fMRI Case Study. Sleep, 35(7), 1017–1020. https://doi.org/10.5665/sleep.1974
Erlacher, D., Schädlich, M., Stumbrys, T., & Schredl, M. (2014). Time for actions in lucid dreams: Effects of task modality, length, and complexity. Frontiers in Psychology, 4, 1013. https://doi.org/10.3389/fpsyg.2013.01013
Hublin, C., Kaprio, J., Partinen, M., & Koskenvuo, M. (1999). Nightmares: Familial aggregation and association with psychiatric disorders in a nationwide twin cohort. American Journal of Medical Genetics, 88(4), 329–336. https://doi.org/10.1002/(SICI)1096-8628(19990820)88:4<329::AID-AJMG8>3.0.CO;2-E
Nielsen, T. A. (2000). A review of mentation in REM and NREM sleep: “Covert” REM sleep as a possible reconciliation of two opposing models. Behavioral and Brain Sciences, 23(6), 851–866. https://doi.org/10.1017/S0140525X0000399X
Siclari, F., Valli, K., & Arnulf, I. (2020). Dreams and nightmares in healthy adults and in patients with sleep and neurological disorders. The Lancet Neurology, 19(10), 849–859. https://doi.org/10.1016/S1474-4422(20)30275-1