Dreaming mainly occurs during REM sleep and takes the form of vivid, dramatic stories of a highly visual nature (or auditory in people blind from birth). Participants woken during REM sleep reported dreaming 80% of the time, so it is likely that we dream every night, even though we may not remember them. Although less common and vivid, dreams may occur in Non-REM sleep.


The content of dreams may be linked to real events before or even during sleep (thirsty people are more likely to dream about drinking) and sex differences have been found: Men are more likely to dream about sexual content and outdoor events than women. Some people are able to control the content of their dreams, known as lucid dreaming.

These theories try to explain the function of the intense neural activity during REM sleep. You should be familiar with their names and authors:

Theory: Evidence for: Evidence against:
Activation-synthesis theory
Hobson & McCarley (1977):
Random bursts of neural activity are made sense of by the brain, this synthesis is expressed in a dream.
Explains dreams about recent events (for example, most recently 'active').

Smell and taste centres do not become active, explaining why we don't dream in these senses.

Injections of the neurotransmitter acetylcholine (responsible for initiating REM sleep) increase the amount of REM sleep and dreaming.

Dreams are influenced by real events, so cannot be caused by totally random activity.
'Reverse learning' theory
Crick & Mitchison (1983):
Dreaming allows unwanted or irrelevant information to be deleted. This means that the brain does not fill up with useless details.
Dolphins and spiny anteaters do not dream and have a massive cortex for their size, maybe to store useless memories. Many dreams have meaningful content - they are not a collection of unwanted memories.

The function of dreaming has psychological explanations, such as problem solving and wish fulfilment. You should be able to describe and evaluate these theories as follows:

Theory: Evidence for: Evidence against:
'Problem-solving' theory
Webb & Cartwright (1978):
Dreams allow people to deal with their problems and come up with solutions ("Let me sleep on it.")
Realistic solutions to problems are more likely to occur after REM sleep.

Longer periods of REM are found in people with relationship or work problems.

Problems can be solved more quickly while awake.
'Wish fulfilment' theory
Freud (1900):
Part of his psychodynamic approach. Dream's manifest content uses symbols to hide the anxiety-causing latent content - a person's unconscious desires.
General agreement that dreams may have meaningful content. Content of dreams is not necessarily disguised in symbols.

Dream interpretation is subjective, so does not provide empirical evidence.