As research on sleep learning and on so-called nondreamers has demonstrated, the memory-processing mechanisms of the brain appear to be switched off (or at least to be “off-line”) during sleep. These findings explain why dreams are often so difficult to remember. Even people who remember their dreams every night only remember the last several dreams they had immediately before awakening. Dreams from the early and middle periods of sleep are permanently forgotten.
A widely utilized method for holding on to dream memories is a dream diary, in which individuals record as many dreams as they can remember immediately upon awakening. Controlled studies have empirically verified the common observation among people who keep dream diaries that this recording must be done immediately, before other thoughts, such as considerations about the upcoming day, are allowed to intrude. In one experiment, for example, participants were instructed to call up for local weather information immediately upon awakening and write down a couple of items from the forecast before recording their dreams. Subjects who completed this task were able to recall far fewer dreams than participants who went immediately to the task of writing down dreams without first telephoning the weather bureau.