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You forget dreams within minutes
Why dreams fade
The hippocampus, the part of the brain that turns short-term memory into long-term memory, stays asleep a little longer than the rest of the brain, so a fresh dream isn't immediately filed away. Two neurotransmitters involved in memory consolidation, acetylcholine and norepinephrine, also dwindle and behave strangely during REM sleep.
Why everyone dreams
That is why dream researchers wake volunteers during REM sleep to get a report, and why people who insist they never dream can describe one when woken in that stage. It is the main reason researchers think everyone dreams.
What helps recall
Waking right out of a dream makes it more likely to stick, and so does an intense or vivid one. Drinking alcohol, smoking pot, and exercising right before bed are among the things that dull recall.
What happens to norepinephrine in REM sleep?
Norepinephrine neurons in the locus coeruleus fire steadily while a person is awake and slow down in non-REM sleep. In REM they fall almost completely silent, which makes REM the one state in which the brain runs without this alertness chemical. Norepinephrine helps mark experiences as worth storing, so in its absence a dream has less to anchor it in memory. Matthew Walker of the University of California, Berkeley has proposed that the low level lets REM sleep process emotional memories without the stress chemistry attached.
Why does alcohol dull dream recall?
Alcohol reduces REM sleep in the first half of the night. As it is cleared from the body, REM often returns later in the night with more intense dreams. Alcohol also tends to make sleep lighter and more broken in the second half. The surge of REM after suppression is called REM rebound.
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