Dreams are so strange and carry so much significance to us that we often feel the need to tell people about our nocturnal adventures, sometimes at tedious length. But if you understand what goes on inside the brain as dreams take their course, they start to make a lot more sense. And dreams are much more important than you might think. Here are some common questions answered about the nighttime hallucinations we call dreams.
There’s a good reason dreams are so skittish and peculiar. Memories of life events — “episodic memories” — are stored in a part of the brain called the hippocampus , and in rapid eye movement (REM), sleep signals coming out of the hippocampus are shut off. That means we can’t access specific memories of things that happened in the past while we dream.
But we can still access general memories about people and places, which form the backbone of our dreams. At the same time, activity in brain regions involved in emotional processes are cranked up, forming an overly emotional narrative that stitches these memories together. As an example, I dreamed recently that a flood had surrounded the house in which I grew up; I needed to try to fly out of the window to escape but I’d forgotten how to fly. The overwhelming feeling was emotion — fear and anxiety about the rising water levels and my inability to fly.
Another part of the brain, the dorsolateral prefrontal cortex, which controls our powers of both logical reasoning and decision-making, is also shut down. I don’t stop to question why the floodwater is rising so fast, or why I’m back in my childhood home, or even why flying to safety is an option.
This difference in brain activity compared with when we are awake helps explain why we feel like we have such scant control over our dreams — we are observers, along for the ride — and why when weird things happen. we don’t raise an eyebrow until we wake up. In my dreams, I often end up breathing underwater, as if it were completely natural.
The study of dreams — which for centuries was more of an exercise in imaginative explanation than anything approaching science — started properly in 1953, when Eugene Aserinsky and Nathaniel Kleitman at the University of Chicago hooked volunteers up to EEGs that detect electrical activity in the brain and woke them during different sleep stages. They discovered REM sleep and its association with dreaming.
Recent experiments have shown that we dream throughout our sleep, and not just in REM sleep, but we forget most of them. Dreams that occur in deep sleep tend to be unemotional, non-vivid, concerned with simple things, and hard to remember. In short, they are boring. REM sleep is where the classic dreams occur, those with bizarre juxtapositions, physically impossible feats, disturbing, moving and puzzling experiences.
Incidentally, many people have wondered if in REM sleep our eyes are moving to “look” at dream images. Some evidence suggests that this is indeed the case.
Some people insist that they never dream, but they are wrong. We know this from experiments that involve waking people at different stages during the night. Everybody dreams, but we don’t all remember them. This could be due to brain activity — those of us who tend to remember dreams have greater activity while asleep and awake in two parts of the brain involved in promoting images and storing memories than people who don’t remember their dreams.
It also has to do with how you sleep. During REM sleep, we struggle to form new memories, says Robert Stickgold , at the division of sleep medicine at Harvard Medical School. If we wake during or just after a dream, however, we are able to grasp hold of it before it slips away — in other words, we can encode it into longer-term storage. So if you wake during the night, you’ll probably remember snatches of dreams you were having. On the other hand, if you wake with an alarm clock and cut short your REM sleep, you are unlikely to keep hold of that memory. That sudden switch of focus from being asleep and dreaming to awake and turning off the alarm interferes with the process of remembering.
There are many ideas about why we dream. One is that they may have an evolutionary function, to test us in scenarios that are important to our survival. This might explain why people often report being chased or attacked in their dreams. On the other hand, many people have attested to the power of dreams for spurring creative thought, such as Paul McCartney, who says the melody to “Yesterday” came to him in a dream (on waking, he improvised lyrics so as not to forget the tune ), and chemist Dmitri Mendeleev who said the structure of the periodic table of elements came to him in a dream. There is experimental support for the idea, with studies showing that people score better on tests of creativity after naps consisting of REM sleep .
Sigmund Freud famously asserted that “the interpretation of dreams is the royal road to a knowledge of the unconscious activities of the mind.” He thought the unconscious was concerned with “deviant” thoughts, and that dreams were primarily a means of wish fulfillment.
While these ideas are now out of favor within science, some interpretation of dreams is possible. What you dream about and the emotional tone of the dream probably reflects what your brain considers important. Research shows that if you play Tetris all day long, your brain will decide that Tetris is what you need to dream about. If you are anxious about something, your brain may well give you a dream with anxiety as the dominant emotion. A huge amount of research logging waking experiences and dream content suggests that your experiences in the day can be mapped to the content of your dream — but a lot, perhaps a majority, of apparently unrelated flotsam also creeps into dreams.
Attempting to analyze and interpret your dreams could be therapeutic or insightful, says Mark Blagrove , of Swansea University, in Wales, but he cautions that some might say that such insight might be no more than you’d get from considering your horoscope or daydreams. Experiments would be needed to test whether dreams in particular convey important personal information. And even then it doesn’t mean dreams are designed to convey that information. If evolution has given us dreams as messages about ourselves, it could have done a better job at making them easier to remember.
Some analyses of dream content suggest that women dream equally about men and women, while men are more likely to dream about other men. Michael Schredl, of the Central Institute of Mental Health, in Mannheim, Germany, has documented dream reports showing that men often dream about fighting other men, while women will dream more often of friendly interactions with people. A couple of years ago, Christina Wong and colleagues at the University of Ottawa wrote a computer program to differentiate between the dreams of men and women. The program correctly predicted the gender of the dreamer about 75 percent of the time. This suggests there may be gender differences in dreaming — but for now it’s too soon to say why.
Hooper is managing editor at New Scientist, from which this is excerpted. His book “Superhuman: Life at the extremes of mental and physical ability ” will be published in May.