Sleep and dreaming

With its increasing emphasis upon functional questions, sleep research has entered a new and exciting third phase. Since sleep had never been objectively studied in any detail prior to the beginning of its first phase in about 1950, it was to be expected that much of the early work in the field would be descriptive. (For reviews ofthe early work, see Jouvet, 1972; Moruzzi, 1972.) Sleep proved a more complex behavior than such distinguished physiologists as In the second phase of sleep research, beginning about 1960, specific mechanistic theories began to be enunciated and tested. New cellular and molecular research techniques produced a spate of findings that have gained conceptual and empirical coherence While incomplete, the mechanistic approach is still going strong, promising to inform-and be informed by-the third phase research on sleep function that has recently been initiated (see reviews, Hobson, 1988Hobson, , 1989)).