Quick: Name something complex and colorful that you created, but that you didn’t intend to create and that you don’t understand even though you made it yourself. Hint: When you created it, you were asleep.

Dreams are a puzzle. We all dream. But it’s difficult to know why we dream, what our dreams mean, or even if there is any meaning hidden amidst the storylines and images we concoct while sleeping.

To understand dreams, a first step is to learn what people dream about. Psychologists have collected dream reports, often by waking people in sleep labs during REM sleep periods and asking them to report their dreams’ contents. Researchers record the content of many people’s dreams and identify common themes.

In one such study (reviewed in Domhoff, 2005), researchers analyzed more than 600 dream reports from 58 research participants. Dreams, they found, often are not as bizarre as you might expect. Although some feature fantastic dream landscapes, the vast majority of dreams took place in locations familiar to dreamers from their everyday life. Similarly, the most common activity in these dreams was routine: talking. Only about 1 out of 20 dream reports contained bizarre content completely unlike that of normal life.

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A European researcher has conducted a statistical analysis of dream content (Schwartz, 2004). She analyzed the storylines of both her own dreams, recorded in a dream diary, and those of 100 college students whose dreams are part of a freely accessible Internet archive of dream reports (dreambank.net). The analysis revealed five types of dream content that were most common:

Again, most dreams were not particularly bizarre; many referred to everyday activities taking place in everyday locations.

One way in which dream content does differ from everyday life is that dreams contain a higher frequency of threats and potential personal harm. In everyday life, we rarely fall through space, run from attackers, or make emergency calls to 911. But in dreams, these sorts of things happen all the time. Analyses of dream content reveals that dreams contain more negative content (fear, threats, harm) than is generally found in everyday life (Valli et al., 2008).

In sum, by analyzing dream diaries, psychologists have characterized the content of dreams. Yet this effort still leaves a major question unanswered: Why do people dream? Let’s try to answer that question now.

There is no one answer to the question of why people dream, rather than spending their nights in dreamless sleep. Instead, psychologists have offered alternative theories of dreaming. Sigmund Freud developed the first of these dream theories.

WISH FULFILLMENT. In his classic work The Interpretation of Dreams (Freud, 1900), Freud proposed that we dream to protect our sleep. Without dreams, Freud believed, our minds’ sexual and aggressive desires (see Chapter 13) would wake us repeatedly.

Specifically, Freud proposed that dreams release unconscious mental energy through wish fulfillment. According to his wish-fulfillment theory, dreams depict the fulfillment of unconscious wishes. By doing so, they drain off some pent-up mental energy, enabling you to stay asleep.

Freud knew that the storylines of dreams often do not appear to fulfill wishes. In fact, they frequently appear to depict just the opposite: something feared rather than something wished for. Freud thought, however, that the storylines of dreams hide their true meaning. If a psychologist, working with the dreamer, could analyze the dream’s meaning fully, he or she inevitably would identify an unconscious wish hidden in the dream’s storyline.

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Freud’s theory was fascinating. However, his scientific evidence was weak. He relied on his own interpretations of people’s dreams. Because Freud naturally had a “rooting interest” in his own theory, it’s possible that his interpretations were biased by his desire to support his own theory. Others, recognizing this limitation in Freud’s work, have developed alternative theories of dreams.

MAKING SENSE OF RANDOM BRAIN SIGNALS. In Freud’s theory, the initial trigger for a dream is highly meaningful: an unconscious desire. In a second theory we will consider now, the initial trigger is psychologically meaningless.

J. Allan Hobson and colleagues (Hobson, 1988; Hobson & McCarley, 1977) have proposed an activation-synthesis theory of dreams. It claims that dreams are produced in two steps. The first is essentially random: During sleep, an area of the brain stem known as the pons (see Chapter 3) generates electrical signals randomly. In the second step, these signals are interpreted by higher regions of the brain that are involved in complex thought. Dreams, then, are simply the brain’s attempt to make sense of random brain signals.

The activation-synthesis model explains one surprising feature of dreams—namely, that they sometimes are bizarre. Although many dreams depict mundane events, as we noted above, some are weird. A person might dream, for example, that “I had to play a game where I was a stealth bomber and I had to bomb a train…. I missed the train and I crashed. Then I appeared by the plane and I walked in with a police officer and we walked into a bedroom in the plane and Clint Eastwood was laying in the bed with one arm in a sling” (from dreambank.net). How could our minds produce such weird storylines? The activation-synthesis theory explains that the brain is trying to make sense of lower-level signals that are utterly meaningless. The brain does its best to create meaning. But, since the original neural signals don’t make sense, the resulting storyline of the dream commonly makes little sense either.

PREPARATION FOR THREAT. Antti Revonsuo, a researcher in Finland, proposes a third theory of dreams (Revonsuo, 2000). It is grounded in a question about evolution: What was the evolutionary function of dreaming—how might dreams have promoted survival and reproduction?

Dreaming, Revonsuo proposes, helps people prepare for everyday threats. In the ancient past, the environment was unrelentingly threatening; predators and harsh weather conditions abounded. The mind’s capacity to create dreams evolved to help cope with the threats. Threats in dreams serve as mental simulations of threats in everyday life. Dreams, then, are a mental “rehearsal”; they activate mental and physical systems needed to cope with threats, including neural systems needed to escape threatening situations. The rehearsals enable people to respond more quickly and effectively to threats in waking life.

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Some evidence supports this theory. As you learned above, dreams often contain threats and feelings of fear. They can be extremely realistic; you feel as if you’re really experiencing the threatening dream content. This realism contributes to the dream’s ability to activate brain systems needed to cope with the real world. Research indicates that brain systems active when people respond quickly to real-life events are also active during REM sleep periods (Revonsuo, 2000).

You’ve just seen three different theories of dreams. The fact that psychology contains more than one theory means that questions about dream life are not entirely answered. Each theory might be partly correct. People experience a wide variety of dreams; different dreams may have different causes; and more than one theoretical idea may be needed to explain all aspects of dreaming.

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