Why Do People Dream?

For so many people, getting into bed at the end of the day is the most wonderful experience. You get to shrug off the stress of the day, close your eyes, and before you know it, you’re off to dreamland. Then you’re falling out of an airplane, being hunted by an axe murderer, or being chased by an enormous bee. Whether you remember it or not, everybody dreams. Sometimes dreams are very pleasant, and sometimes they’re downright terrifying. Dreams are an integral part of most people’s nightly life but where do they come from and why do people dream?

To better understand dreams, we first have to look at why we sleep in the first place. When you sleep, you fall into an anabolic state, in which your body repairs and builds the immune, nervous, skeletal and muscular systems. As any student will tell you, bad things start to happen when you don’t get enough sleep. This condition is known as sleep deprivation, and it can lead to problems such as fatigue, sleepiness, clumsiness, and weight loss or weight gain, depending on the individual. After a certain amount of time without sleep, you simply can’t function, according to sleep experts.

Getting between roughly 7 and 9 hours of sleep per night is ideal: that gives your body enough time to essentially run a system check and release hormones that help maintain your immune system and retain memory. Once your head hits the pillow and you drift off, your unconscious body takes over and sleep proceeds in cycles of REM sleep about four or five times per night. What happens during those eight hours of unconsciousness? What’s the brain doing that gives us those sometimes vivid and possibly bizarre dreams?

Dreams occur during REM sleep. REM stands for rapid eye movement, and during this stage your eyes are doing just that—they dart around under your eyelids like little pinballs. Other characteristics of REM sleep include paralysis, where signals are sent to the spinal cord commanding it to shutoff movement; stimulation in the regions of the brain that are used for learning; and signals being sent to the brain cerebral cortex which is the region responsible for learning, thinking and organizing information. Dreams are most likely in the last third or so of the night because this is when the effects of REM sleep are the strongest.

Children are afflicted with nightmares at a higher rate than adults, at 10-50 percent versus 2-8 percent. The portion of the brain known as the amygdala is likely responsible for those unpleasant visions, as neuroimaging studies have shown it to be highly active during REM sleep, as well as during the day when a person is dealing with negative emotions. When you’re awake, you can think logically and dismiss these negative thoughts, but when your body and parts of your brain are unconscious, you become trapped in your own mind and this can lead to nightmares.

Other factors that influence nightmare frequency and severity are past trauma, security and important life changes. These negative emotions often manifest themselves as symbols or metaphors in our dreams. The end of a relationship could show up as an ax-murderer, symbolizing a chapter of life brought forcefully to a close.

Scientists have yet to fully understand exactly why we dream. Of all the signals sent to the cerebral cortex during REM sleep, some of them seem to be random. Scientists believe that these random signals are the bedrock of dreaming, as the brain may be trying to interpret these random signals, resulting in dreams. Dreams also tend to mimic recent experiences. For example, if the previous day you were learning to drive, the brain is likely to recall those electrical impulses and replay them. Then, since you don’t actually see anything when you’re asleep, in order to make sense of those impulses, the brain conjures up memories from random days and events, which can explain the strangeness we experience in many dreams.

One likely cause for dreams is that during REM sleep your brain is acting as though it’s wide awake, even though your body is unconscious. The full responsibility of generating images and feelings therefore falls to the brain, and without the aid of a conscious body, the images that it that draws can be very vague or bizarre. As of now, researchers can’t directly access dreams, so studying them is more difficult than most other subjects, and it often requires less precise methods, such as provoking subjects to wake up suddenly during their sleep to record their experiences.

However, there is a group working on a machine-learning based analysis of dreams. Here’s how it works: participants are hooked up to an electroencephalograph machine or EEG and then fall asleep inside an fMRI machine. The subjects are then woken up as soon as an electroencephalogram signature is detected, on average roughly three hundred forty-two seconds after falling asleep, and they’re asked to describe their visual experiences before awakening.

This procedure is repeated to attain at least 200 awakenings, with a visual report for each participant. From the collected reports, the words that subjects used to describe their dreams are mapped into wordnet, a lexical database in which similar words are grouped, into what are called Six S, in a hierarchical structure. The researchers then gather images corresponding with those words to train their learning algorithm. This algorithm is so advanced, it’s able to utilize the fMRI data to essentially recreate dreams in video form using the input training images.

One interesting thing to note about this particular study is that it questions the idea that REM sleep is when most dreaming occurs. Researchers found that dreams can and do occur in sleep stages 1 & 2. This allowed them to save time by waking up their subjects much earlier into their sleep cycles. Though this learning algorithm is far from perfect and does take a large individualized time commitment, it does bode well for the future of dream science. Maybe someday we’ll even get to record our dreams and play them back whenever we want.

For more about the interesting things that happen with our brains and bodies while we sleep, check out why do people sleepwalk. Happy dreaming!