According to a report published on Medical News Today:
"Scientists have long puzzled over the many hours we spend in light, dreamless slumber. But a new study from the University of California, Berkeley, suggests we're busy recharging our brain's learning capacity during this traditionally undervalued phase of sleep, which can take up half the night.
UC Berkeley researchers have found compelling evidence that bursts of brain waves known as "sleep spindles" may be networking between key regions of the brain to clear a path to learning. These electrical impulses help to shift fact-based memories from the brain's hippocampus - which has limited storage space - to the prefrontal cortex's "hard drive," thus freeing up the hippocampus to take in fresh data. Spindles are fast pulses of electricity generated during non-REM sleep, and they can occur up to 1,000 times a night.
"All these pieces of the puzzle tell a consistent and compelling story - that sleep spindles predict learning refreshment," said Matthew Walker, associate professor of psychology and neuroscience at UC Berkeley and senior author of the study to be published March 8 in the journal Current Biology.
The study found that this spindle-driven networking was most likely to happen during Stage 2 of non-Rapid Eye Movement (NREM) sleep, which occurs before we reach the deepest NREM sleep and the dream state known as Rapid Eye Movement (REM) sleep. This shallow stage of dreamless slumber can account for half our sleeping hours, and happens most frequently during the second half of the night, or in the latter part of a period in which we sleep.
"A lot of that spindle-rich sleep is occurring the second half of the night, so if you sleep six hours or less, you are shortchanging yourself. You will have fewer spindles, and you might not be able to learn as much," said Bryce Mander, a post-doctoral fellow in psychology at UC Berkeley and lead author of the study.
You can find the full article here.