Intense emotion is a key feature that distinguishes dreams from waking life. Most dreams are unpleasant: fear and anxiety are the dominant emotions, with anger close behind. This combination outweighs the other top emotion in dreams, elation.

This pattern suggests that dreaming sleep involves selective activation of areas of the brain that respond to danger. This makes sense from an evolutionary viewpoint, says J. Allan Hobson of Harvard University, one of eight distinguished neuroscientists whose essays comprise this book. Consider how vulnerable animals are when sleeping. Being vigilant enough to awaken if predators are nearby--or if burglars break into your home--is an important survival tool.

Dreaming is a delusional state: we accept acts such as flying or encounters with long-dead relatives as plausible while we dream. Severe memory loss accompanies this state: how else to explain why we at best remember only part of the thoughts that occupy our minds for 90 minutes- to two hours each night? "If we can begin to get a fix on how dreaming works, we will have a blueprint for beginning to understand how the symptoms that are normally confined to sleep may arise when we are awake," Hobson writes, "enabling us to reach into the mental hospitals and into the minds of afflicted fellow humans."

This goal intrigued Freud, who saw dream interpretation as "the royal road to a knowledge of the unconscious activities of the mind." It also fueled early sleep laboratory studies in the 1950s, following the seminal discovery that waking sleepers while their eyes darted rapidly beneath closed eyelids--a state of sleep dubbed rapid eye movement or REM sleep--produced reports of vivid dreams. Waking sleepers at other times elicited more mundane thoughts.

Hobson's research suggests chemical mechanisms turn certain parts of the brain on and off in sleep and dreaming. The visual part of the brain, for example, receives stimulation not from the eyes, but from the brain stem, specifically the pons. Recordings of electrical signals from a single cell in the pons show wild and spontaneous firing, much like an epileptic seizure. On a large scale these signals radiate through out the brain, triggering memory fragments and false sensations, such as the feeling of wanting to run, yet being frozen in place. When the cortex, the thinking part of the brain, processes these signals, Hobson says, it tries to make sense of them, weaving them into stories that are as coherent as possible under the circumstances. These fanciful tales are our dreams.

Dreams are not "nonsense," Hobson says. Rather, they are something like a Rorschach test, revealing interesting aspects of the dreamer's inner life.

This and other essays in this book were derived from a series of lectures for the general public co-sponsored by the Dana Alliance for Brain Initiatives and the Smithsonian Associates. In other essays, Steven Hyman explores origins of addiction and severe mental illness, Jerome Kagan asks whether genes determine personality, and Kay Redfield Jamison examines ties between madness and creativity. Bruce McEwen looks at how chronic stress compromises memory, and Esther Sternberg charts the impact of emotions on physical illness. Joseph LeDoux examines the biology of fear, while Eric Kandel explores how memory works. As a group, these essays offer a wide-ranging state-of-the-art view on how our brains influence our health, behavior, feelings, and identities.

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