Woke up with a feeling of anxiety and sadness. “Must be a dream.” “What was it?” No memory.
Why does that happen? Why do you feel the emotions but not remember the dream?
When we’re awake, norepinephrine plays a role in encoding new experiences and locking them in as long-term memory. During REM sleep, serotonin and norepinephrine signaling drops, and the memory doesn’t form.
The rush of emotion is driven by acetylcholine, the brain doesn’t go quiet while we’re sleeping; dreams in REM sleep feel vivid because of acetylcholine. A trade-off happens here: as acetylcholine increases, the chemical activity responsible for memory formation decreases. The hippocampus, the brain’s memory-forming region, also becomes less active, so while our vision and brain are firing away, creating roller-coaster dreams, it isn’t working to fill us in with the details later.
Research in Japan suggests specific neurons in the hypothalamus, called MCH neurons, are active during REM sleep and appear to actively suppress memory formation. This reframes forgetting dreams not as a passive failure, but as the brain possibly doing deliberate cleanup work, closer to intentional pruning than an accident.
Once we wake up, there’s a small window, 30 seconds to 5 minutes, where if you’ve written a dream down or spoken about it, you may retain the details. Otherwise, like a whoosh, the memory fades.
Have you also felt frustrated when you couldn’t remember a dream that made you feel emotional for no reason?
MBH/PS