Why dreams get more bizarre further into the night

Updated: May 23

How important are the contents of a dream? While some would say that they reflect the deepest desires of the dreamer, others insist they are best forgotten in the morning because they have no practical significance. Some people would even say that dreams reflect nothing but random firing of neurons (do they know what 'random' means?).

If dreams offer an experiential window into sleep (transparency assumption), then dream content should clearly mirror stage-of-sleep differences in sleep-dependent cognitive processes. Indeed, this has been found across many research studies.
Malinowski and Horton, 2020

The creatures that populate dreams may or may not have personal wisdom to impart, but they are invaluable to researchers trying to understand why we dream. Studies have shown that the contents of dreams change dependably based on the stage of sleep. For example, REM (Random Eye Movement) sleep, more common in the second half of sleep cycle, features dreams that are more vivid, emotional and bizarre compared to non-REM sleep.

In a study by Josie Malinowski and Caroline Horton, participants (N = 68) were awoken at four pre-determined points during sleep and recorded their dreams. They also recorded their waking-life activities, and how continuous their dreams were with waking-life experiences.

Researchers found that early-night dreams were more continuous with waking life than late-night dreams. Dream reports from early night (first four hours of sleep) were more obviously relatable to waking life. They featured episodes from the dreamer's recent past to the anticipated future.

Late-night dreams were more intense, emotional and personally important. They were more bizarre, abstract and metaphorical than early-night dreams. They featured episodes from the distant past. The researchers opine that the 'hyperassociative' nature of late-night dreams (reflected by its increased bizarreness, metaphoricity and time orientation variance) suggests the formation of fluid associations between items in memory.

According to the researchers, while early-night sleep consolidates episodic memory from the recent past, late-night REM sleep may help embed individual memories within the greater network of memories through hyperlinks (by forming fluid associations as revealed by hyperassociative dreams during this stage of sleep). Indeed, previous research has shown that REM sleep is crucial for creative, abstract, and associative thinking in waking life. Read more about the study here.