dream

Series of events or images perceived through the mind during sleep. Their function is unknown, but Sigmund Freud saw them as wish fulfilment (nightmares being failed dreams prompted by fears of ‘repressed’ impulses). Dreams occur in periods of rapid eye movement (REM) by the sleeper, when the cortex of the brain is approximately as active as in waking hours. Dreams occupy about a fifth of sleeping time.

If a high level of acetylcholine (chemical responsible for transmission of nerve impulses) is present, dreams occur too early in sleep, causing wakefulness, confusion, and depression, which suggests that a form of memory search is involved. Prevention of dreaming, by taking sleeping pills, for example, has similar unpleasant results. For the purposes of (allegedly) foretelling the future, dreams fell into disrepute in the scientific atmosphere of the 18th century.

Lucid dreaming is where the dreamer is actually aware that they are in a dream and can control events to some extent. Approximately 60% of adults will experience a lucid dream, and 16% experience them monthly.