Dreams can usually be recalled if a person is awakened while dreaming. Women tend to have more frequent dream recall than men. Dreams that are difficult to recall may be characterized by relatively little affect, and factors such as salience, arousal, and interference play a role in dream recall. Often, a dream may be recalled upon viewing or hearing a random trigger or stimulus. The salience hypothesis proposes that dream content that is salient, that is, novel, intense, or unusual, is more easily remembered. There is considerable evidence that vivid, intense, or unusual dream content is more frequently recalled. A dream journal can be used to assist dream recall, for personal interest or psychotherapy purposes. Adults report remembering around two dreams per week, on average. Unless a dream is particularly vivid and if one wakes during or immediately after it, the content of the dream is typically not remembered. Recording or reconstructing dreams may one day assist with dream recall. Using the permitted non-invasive technologies, functional magnetic resonance imaging (fMRI) and electromyography (EMG), researchers have been able to identify basic dream imagery, dream speech activity and dream motor behavior (such as walking and hand movements).In line with the salience hypothesis, there is considerable evidence that people who have more vivid, intense or unusual dreams show better recall. There is evidence that continuity of consciousness is related to recall. Specifically, people who have vivid and unusual experiences during the day tend to have more memorable dream content and hence better dream recall.
The brain activity capable of formulating such dreams, rare among literate people in later eras, conforms to the bicameral mentality hypothesized by Julian Jaynes as dominant into the second or first millennium BCE. Framing the dream experience varies across cultures as well as through time. Dreaming and sleep are intertwined. Dreams occur mainly in the rapid-eye movement (REM) stage of sleep—when brain activity is high and resembles that of being awake. Because REM sleep is detectable in many species, and because research suggests that all mammals experience REM, linking dreams to REM sleep has led to conjectures that animals dream. However, humans dream during non-REM sleep, also, and not all REM awakenings elicit dream reports. To be studied, a dream must first be reduced to a verbal report, which is an account of the subjects memory of the dream, not the subjects dream experience itself. So, dreaming by non-humans is currently unprovable, as is dreaming by human fetuses and pre-verbal infants. Subjective experience
Preserved writings from early Mediterranean civilizations indicate a relatively abrupt change in subjective dream experience between Bronze Age antiquity and the beginnings of the classical era.In visitation dreams reported in ancient writings, dreamers were largely passive in their dreams, and visual content served primarily to frame authoritative auditory messaging. Gudea, the king of the Sumerian city-state of Lagash (reigned c. 2144–2124 BCE), rebuilt the temple of Ningirsu as the result of a dream in which he was told to do so.