Why do we dream?
The longest, most story-like dreams occur during REM sleep, of which there are four or five cycles a night, growing longer towards morning — which is why we usually remember the last one before waking. Research suggests this is when memory is organised and emotional load is processed: the brain replays the events of the day and links them to older memories. That explains why decades-old memories mix with yesterday's irritation. Psychological interpretation, from Freud to Jung, builds on this: if a dream's images are made from our own material, then which image the mind reached for also says something about us.


