During sleep, a person goes through four to five REM periods. REMs are rapid eye movement states that last 30 to 90 minutes. During REM periods, brain waves detected by electroencephalography are similar to those of an awake person. In addition to REM periods, sleeping people experience periods of NREM, that is, non-rapid eye movements. NREM periods occur between REM periods and last as long as the REM periods. Dreams occur most often during REM cycles due to increased brain wave activity. Dreams can occur during periods of NREM sleep, but they are not as common and tend to be less visual. On average, a person has a dream one night out of three, whether they are able to remember it or not. Dreams are more common in infants and gradually diminish as they age