Of all the components of a good night's sleep, dreams seem to be least within our control. In dreams, a window opens into a world where logic is suspended and dead people speak. A century ago, Freud formulated his revolutionary theory that dreams were the disguised shadows of our unconscious desires and rears, by the late 1970s. neurologists had switched to thinking of them as just “mental noise” the random byproducts of the neural-repair work that goes on during sleep. Now researchers suspect that dreams are part of the mind's emotional thermostat, regulating moods while the brain is “off-line”. And one leading authority says that these intensely powerful mental events can be not only harnessed but actually brought under conscious control, to help us sleep and feel better, “It's your dream” says Rosalind Cartwright, chair of psychology at Chicago's Medical Center. “If you don't like it, change it.”

　　Evidence from brain imaging supports this view. The brain is as active during REM (rapid eye movement) sleep-when most vivid dreams occur-as it is when fully awake, says Dr, Eric Nofzinger at the University of Pittsburgh. But not all parts of the brain are equally involved, the limbic system (the “emotional brain”)is especially active, while the prefrontal cortex (the center of intellect and reasoning) is relatively quiet. “We wake up from dreams happy of depressed, and those feelings can stay with us all day” says Stanford sleep researcher Dr, William Dement.