REM sleep and the concept of vigilance

Several writers, notably Montague Ullman and Frederick Snyder, conceive of REM sleep and the associated state of vivid dreaming as periods of vigilance. In Ullman's conceptualization, the emphasis is on dreaming in humans, whereas Snyder is concerned with REM sleep (activated sleep) in subhuman organisms. In this paper several objections to the sentinel and vigilance theories are raised, and a modified concept of vigilance, linking it with learning and memory, is put forward.