DREAMING: An Introduction to the Science of Sleep. By J. Allan Hobson. Oxford Univ. Press. 170 pp. $22

In June, sleep specialists from around the world will gather in Chicago to celebrate the 50th anniversary of the discovery of rapid eye movement (REM) sleep, the state in which our most vivid dreams occur. At the University of Chicago in 1953, graduate student Eugene Aserinsky and physiologist Nathaniel Kleitman found that sleepers’ eyes dart beneath closed lids roughly every 90 minutes. These episodes last only a few minutes early in sleep but close to an hour later on. People awakened during REM sleep usually report dreams with visual images and storylike narratives. Those awakened while their eyes are at rest seldom do, though they sometimes recall prosaic thoughts.

With the discovery of REM, Aserinsky and Kleitman revolutionized the scientific study of sleep. They showed that sleep is not, as previously thought, a uniform and passive state. The brain proves as active in REM sleep as in waking, sometimes more so.

Changes in the level of brain activation shape the content of our dreams, J. Allan Hobson contends in this book. A psychiatrist who directs the neurophysiology and sleep laboratory at Harvard Medical School, Hobson threw the sleep and psychoanalytic communities into a tizzy in 1977 when he and his colleague Robert McCarley proposed that dreams reflect the waking brain’s efforts to make sense of randomly generated signals. This theory challenged the Freudian notion that dreams originate in disguised wishes. Hobson and McCarley were castigated for claiming that dreams lack meaning.

Not so, Hobson takes pains to emphasize here. Indeed, he maintains that dreams offer insight into our waking lives. He includes selections from some of the more than 300 of his own dreams he has recorded in the past 25 years, and discusses the events and feelings they depict. Understanding how we create dream stories, he writes, helps illuminate the nature of consciousness, "our most interesting human attribute."

In REM sleep, brain areas that control vision and emotions turn on. Positron emission tomography (PET) scans reveal increased activity in regions that generate hallucinations. At the same time, noradrenaline and serotonin—two chemicals critical to logical thinking, focusing, and memory— turn off. Their absence renders dream stories strange, implausible, and hard to remember (most of us recall dreams infrequently, and when we do, we may retain only one or two of the four or five dreams of a typical night). In REM sleep, the brain generates motor signals but squelches our ability to act on them. We may perceive that we fight assailants, flee from danger, or make passionate love, yet we barely twitch in our beds.

Sigmund Freud thought the bizarreness of dreams allowed sleepers to avoid acknowledging subconscious wishes. But Hobson believes that the weird stories more likely reflect the brain’s astounding ability to link a profusion of tangentially related ideas, which he terms "hyperassociation." We’ve all had dreams in which scenes change abruptly. In one experiment, Hobson and colleagues scissored apart 10 dream reports at the point of these dramatic scene shifts. They then spliced the fragments together, restoring half to their original form and making hybrids of the rest by combining the first part of one person’s dream with the second part of another’s. Even skilled psychoanalysts couldn’t distinguish the real dreams from the hybrids. In trying to make sense of our dreams, Hobson believes, we search for causal ties where none exist.

Why do we dream at all? Through activation of the brain in sleep, Hobson suggests, we assimilate new information, master new skills, and prune out-of-date files. Babies get much more REM sleep than adults; intense activation may foster brain development early in life.

Freud initially aspired to unite psychology and neurology. In his Project for a Scientific Psychology (1895), he tried to construct a model of the human mind by describing its neurobiological workings. Since the neurological techniques of his time weren’t up to the task, he concentrated on psychological theories. Today, PET scans and other sophisticated imaging tools open new windows to understanding how the brain functions. Contemporary neuroscientists can mine a trove of data that Freud could only dream of.

—Lynne Lamberg