The Purpose of Dreams and Other Cutting-Edge Research on Sleep
The Purpose of Dreams and Other Cutting-Edge Research on Sleep
Every month, we get into a different health topic and explore the research. This month, we’re looking into recent studies on sleep and summarizing the most interesting findings.
But first, a recap of sleep cycles: There are four stages during sleep. When a person first falls asleep, they are in N1 sleep, which is a light sleep from which they can easily be awoken. Next they transition into N2, which is the second phase of light sleep. People spend the majority of their night in this phase. The third phase of sleep is called N3, slow wave, delta, or deep sleep because the person becomes less responsive—their heart rate, breathing, and blood pressure drop. Last is rapid eye movement (REM) sleep. During this phase, your eyes dart around inside your eyelids, and it’s when you experience the majority of your dreams. The average adult goes through all four stages about three to five times a night, with the REM phase becoming progressively longer with each cycle.
Social Cognitive and
Affective Neuroscience (2018)
It’s long been unclear whether dreams serve a purpose—and if they do, what exactly that purpose is. In many ancient civilizations, dreams were heavily interpreted and believed to be prophetic. Psychologist Sigmund Freud believed that dreams were a path to understanding the unconscious mind; many other psychologists and scientists believe that dreams don’t mean anything and are just random electrical impulses from the brain.
More recently, scientists have discovered that we tend to dream images from events that have occurred throughout our day. And we’re beginning to discover that dreams may serve a larger purpose—such as processing emotions.
Researchers from the Department of Psychology at Swansea University in Wales recruited twenty university students (ten men and ten women) who reported being able to frequently remember their dreams. For ten days, the participants were asked to keep a daily log of their activities, major concerns, and any personally significant events, as well as the emotional intensity of these events. On the tenth day, participants slept in a sleep laboratory with electrodes on their head. Researchers woke them during their slow wave sleep and REM sleep and then asked them to recall any dreams they’d had. If the student remembered their dream, researchers woke them ten minutes into the following REM phase. If the student did not remember their dream, researchers woke them during the following slow wave sleep phase and asked them to recall their dream again. Three weeks later, participants were given sheets of paper with their daily logs on the left and their dream reports on the right in random pairings. Participants were asked to identify any similarities between the two (such as common people, themes, objects, or events) and rate the level of match on a scale. Two independent judges also conducted blind ratings of the correspondence between day and dream content.
After data analysis, the researchers found that when participants were awoken during REM, they were more likely to report dreams than when they were awoken during slow wave sleep. And they were also able to remember more of their dreams when they were awoken during REM. The researchers found that the number of recent memories (from within one to two days) that were incorporated into dreams was higher during periods of REM, when theta brain waves were more active. (Frontal theta waves are considered a dominant feature of REM sleep.) They also found that intense emotional memories were more likely to be incorporated into dreams than less emotional memories.
The two main takeaways: Emotionally intense experiences are more likely to be dreamed about, and theta brain waves during REM sleep cycles may be one mechanism by which the brain consolidates these memories. Other studies have suggested that REM sleep may play a role in trauma recovery and mood regulation by allowing the brain to process difficult memories.
Human Brain Mapping (2019)
So what about bad dreams—do they serve a greater purpose?
Researchers from the University of Geneva in Switzerland studied eighteen participants while they were sleeping, placing electrodes on their heads to measure their brain activity. The researchers woke participants several times during their sleep to ask them if they were dreaming and if they were scared in their dream. Participants’ brain activity data showed that having a scary dream activated two main brain regions: the insula (which mediates fear and anxiety) and the cingulate cortex (which plays a role in preparing the body to respond to threat).
Next participants filled out a dream diary for a week, detailing what they remembered from their dreams in the morning and any emotions they felt. At the end of the week, MRI machines scanned their brain activity while they were shown emotionally evocative images, negative images (such as a fight), or neutral images. The researchers found that participants who reported feeling fear more often in their dreams had less activity in areas of their brain associated with emotion regulation when they were shown negative images. These participants had more activity in their medial prefrontal cortex, which is known to reduce the fear response produced by the amygdala. Which means: The emotions that participants felt during their dreams were inversely associated with the intensity of their brain’s response to emotionally evocative images they saw while they were awake. The researchers believe that this means that dreams serve as a type of training ground that can prepare our minds for danger and fear in the real world.
It’s well known that sleep is controlled by our circadian rhythm: the internal clock that responds to light and dark by increasing our wakefulness or inducing sleep. But sleep is also controlled by something that’s less known—and less studied—called our homeostatic processes. These processes control our body’s internal stability in response to environmental changes, such as intense heat or a stressful day. Together, circadian rhythms and homeostatic processes interact to control our sleep-wake cycles.
To better understand these homeostatic processes and how they relate to sleep, researchers from University College London studied the brains of zebrafish, giving them caffeine and other stimulants to increase their brain activity during the day. Later, the researchers studied the fish and took brain measurements while they slept. The fish who had been fed stimulants slept for much longer than normal, meaning: Heightened brain activity during the day increased their need for rest. And the researchers found that there was a specific area of the brain that lit up when the fish were in this sort of recovery sleep that did not light up during their normal sleep. Here, the researchers identified a brain signaling molecule called galanin that was also overly active during recovery sleep.
The researchers then studied the fish under a different set of conditions that would also affect their homeostatic processes: a simulated fish treadmill. They showed the fish images of moving stripes to make them believe that they were moving through water quickly, which kept them continuously swimming. As when they were given stimulants, when the fish were finally allowed to sleep, they slept for much longer than normal and had increased galanin activity in certain brain regions.
This study suggests that it’s not just light and dark cues that control our need for sleep. Our bodies keep track of strenuous activity and subsequently need more rest to make up for it. While this study was just in fish, the researchers believe that humans’ sleep is also influenced by galanin and its related genes, which, with further study, could help scientists better understand why we sleep—and why some people with sleep disorders don’t sleep as well.
Journal of the American
College of Cardiology (2019)
As anyone who’s had a less-than-perfect night’s rest knows, sleep has a huge impact on our overall functioning and health. While the lens often focuses on lack of sleep as the culprit, new research suggests that oversleeping can be detrimental to our well-being, too.
Researchers from the Broad Institute of MIT and Harvard recruited more than 460,000 participants between forty and sixty-nine years old from the ongoing UK Biobank cohort study. At the start of the study, participants were asked how many hours of sleep they get per night on average. A study nurse took samples of each person’s blood, saliva, and urine. Hospital data and death registries were used to ascertain cardiovascular-related events and deaths. The researchers calculated each participant’s genetic risk of coronary artery disease using data from genome-wide association studies, which map out genetic variants in different individuals to determine whether there are similarities that are commonly associated with particular traits or outcomes. Using this data, participants were classified as high, medium, or low risk for CAD. The researchers also identified several genetic signatures related to sleeping for a short or long time that were used to reduce error from the participants’ self-reported sleep duration. Using this genetic data allowed the researchers to better assess causality between sleep duration and cardiovascular events, which has been notoriously hard to do in similar studies.
People who averaged less than six hours of sleep per night and those who averaged more than nine hours of sleep per night had a significantly increased risk of heart attack. The oversleepers were 34 percent more likely to have had a heart attack than those who slept between six and nine hours, while the undersleepers were 20 percent more likely. When the researchers analyzed genetic risk, they found that those with the highest genetic risk of CAD had a 91 percent higher risk of heart attack than those with the lowest genetic risk. Those with high genetic risk of CAD who got too much or too little sleep were 130 percent more likely to have had a heart attack than those with low genetic risk who got between six and nine hours of sleep.
This study shows that sleep duration may be a risk factor for heart attack regardless of a person’s genetic risk, emphasizing the need for people to get between six and nine hours of sleep a night. And perhaps even more importantly, this study suggests that the right amount of sleep may mitigate the risk of heart attack for those who are genetically predisposed.
This article is for informational purposes only. It is not, nor is it intended to be, a substitute for professional medical advice, diagnosis, or treatment and should never be relied upon for specific medical advice. To the extent that this article features the advice of physicians or medical practitioners, the views expressed are the views of the cited expert and do not necessarily represent the views of goop.