Dreams Are Doing A Lot More Than Entertaining Your Sleeping Brain

Science is built upon laws and principles that are immutable. What then can a scientist make of the world of dreams, where time can warp and the laws of physics shatter? Some people argue that there is no rhyme or reason to the content of our dreams. The "activation-synthesis theory" posits that dreams are just moments of random neurological activity that occur in the brainstem as we sleep, and that our sense of dreams having a narrative only comes from the forebrain trying to piece these unrelated moments together. That would certainly explain why some dreams can be so confusing, but many scientists believe there's more purpose to them. A growing body of research now suggests that dreaming helps us process the information we consume during consciousness, and most crucially, learn from it.

This brings us to another concept known as the "threat simulation theory," which hypothesizes that dreams are a biological means of conditioning ourselves for the dangers of the real world. By simulating dangerous situations, dreams may strengthen the neurological mechanisms that help us identify threats and respond by either avoiding or facing them. Studies on the body's reaction to horror movies show that even the suggestion of danger is enough to activate a physiological response, and dreams could be doing something similar. This puts more weight on dreams than activation-synthesis theory, but both hypotheses leave big questions. Threat simulation theory makes sense for nightmares, but what about good dreams, or dreams that are just plain weird?

Most of the dreaming we do occurs during the REM (rapid eye movement) stage of sleep, and this provides a significant clue to the true function of dreams. REM sleep comes with a surge of neurological activity that closely mirrors that of the brain during waking hours. This is why dreams in the REM stage are the most intense, despite the fact that you can actually dream during any stage of sleep. There's another aspect of REM sleep that may be even more significant to our dreams though; it's the stage in which our brains perform self-maintenance.

A 2017 sleep study conducted by an international team of scientists at Peking University and NYU revealed that neural synapses undergo a kind of cleanup process during REM sleep. Some synapses are strengthened while others are eliminated. This suggests that the brain is basically sorting through all of the information it picked up over the course of the day and selecting what it needs to save and what it can do without. Dreams likely play a role in this process.

Perhaps the best evidence for the role of dreams in learning comes not from any human study, but from a study of birds. Research published in 2000 monitored the neural activity of zebra finches while they slept, and found that the birds experienced the exact same activity as when they sang. Researchers interpret this as the birds "rehearsing" their songs in their dreams in order to perfect them.

The apparent significance of dreams might get some people worried about whether or not they are dreaming enough. There is a rare condition called Charcot–Wilbrand syndrome which causes people to stop dreaming altogether, but it is only known to be triggered by trauma to the brain, such as an injury or stroke. Even then, it is an exceedingly uncommon condition and may only be temporary in many patients. Despite this, a survey of 1,000 Americans conducted by the bedding company Purple found that nearly 20% of respondents experience no dreams. Did all those people have Charcot–Wilbrand? No; the answer is much simpler. Those respondents who reported having no dreams actually were dreaming all along, they just couldn't remember it.

During REM sleep, we actually lose most of our ability to make new memories. It makes sense; REM sleep is the time when our brain processes the information we absorbed while we were awake, so it can't also be adding new memories at that moment. However, this means that it is extremely difficult to remember dreams in detail, if at all. Even when you do remember a dream, it's probably only the last dream you had before waking up, when across the course of a full night, most people have four to six dreams. Sleep disorders such as insomnia (which may not be your fault) or sleep apnea, can disrupt a healthy sleep cycle and make for less vivid and less memorable dreams, which is just one more reason that sleep hygiene is so important.