What have I learned in my sleep tonight? A heavy rain and a (branch?) crash on the roof wakes me at 4:00 am. In a cold sweat, my ears ringing loud with tinnitus, I hear the powerful howling wind and think that all this fury is still miniscule compared to what could be unleashed. I am in awe, humbled by it, amazed by it.
As I listen it fades to a slow mellow reassuring patter.
I wake again, it’s at 6 am.
When we sleep, long term memory consolidation happens. Memories during all sleep stages, (light, deep, and REM) get formed, pruned, entrenched and cemented.
The short-term memory is thought to be encoded as patterns of neural activity while long-term memories are structural changes in the brain – the formation of new synapses that are more persistent. This explains why short-term amnesia can happen (memory from the last 12 hours or so is wiped) without affecting long-term memories.
“Consolidation” means some neural circuits are strengthened and others are erased and or let go so that new memories can form.
Scholars Ken A. Paller and Joel L. Voss wrote an article in 2004 laying out their hypothesis that pruning of available memory happens at night as the brain shuffles and adopts what it will put into declarative memory. Declarative memory is defined here as the ability to recall specific facts and events, as opposed to background knowledge and emotions. And that when it comes to an individual’s understanding of the world “sleep is essentially a nightly session of psychotherapy” in the words of these Northwestern University scientists (This analogy may not be perfect.)
The communication between the hippocampus and neocortex allows new data learned the previous day to “update” understanding in the neocortex. Electrophysiological, computational and neuroimaging studies have shown information transfers to the neocortex. The schematized versions of some of the short-term memories contribute to learning so that even when memory of a specific event is gone, that event still contributed to overall knowledge.
Particularly during stage 3 deep sleep, the memories that have been put in the hippocampus (short-term memories formed during the previous day) are redistributed to the neocortex (where they will be long-term memories).
This transfer of information happens during waking hours, too, as well as NREM sleep. During REM sleep there is not much communication between these two areas of the brain. Instead, the neocortex replays memories to itself.
That’s one way to think of dreams, as the brain replaying memories to itself. Dreams, neuroscientists think, result from the work the brain does in storing memories.
All this memory maintenance seemed to ignore and suppress the senses but there is new evidence that we can subconsciously learn from external stimuli in our sleep.
Researchers showed that we can acquire the vocabulary of a new language during distinct phases of slow-wave sleep and that the sleep-learned vocabulary could be retrieved unconsciously following waking. Memory formation appeared to be mediated by the same brain structures that also mediate wake vocabulary learning.
… There is considerable evidence for wake-learned information undergoing a recapitulation by replay in the sleeping brain. The replay during sleep strengthens the still fragile memory traces und embeds the newly acquired information in the preexisting store of knowledge.
It is 6:45 am, something big crashes and moves branches outside twice. I check, but nothing is there. No wind, no pile of branches, no tree braches touching the roof. First mystery of the day. Will it be stored long term in tomorrow nights sleep?