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In the grand scheme of things, the field of sleep science is new — very new. While we still can’t say with certainty why we sleep, experts in shut-eye have, over the past 60 years, made staggering strides in dissecting our rest. (Here’s a refresher we published in October on watershed moments in the history of sleep research.)

In 2015 alone, we saw a consistent stream of sleep-related studies clogging our news feeds. Many are fascinating, some are terrifying. Some are, truth be told, way over our heads.

Here’s a sampling of some of this year's most important findings in the field of sleep. 

Our ancestors probably slept a lot like we do now.

Fred Flintstone Sleeping Patterns

Two big studies on the evolution of sleep challenged the notion that humans slept in multiple, shorter chunks (or, “polyphasic sleep”) until the industrial revolution, when artificial light ended the reign of segmented rest. Research teams compared our sleep habits to those of “modern-day” hunter-and-gatherer societies, as well as to our 21 closest primate species. The verdict from both groups? Monophasic sleep is literally ancient news and likely far from accidental. Will 2016 see a rebuttal from team-polyphasic sleep?

If you don’t sleep tonight, you may not remember this sentence tomorrow.

Brain Scan Memory Recall

Rest facilitates memory formation, solidification and retrieval. Both slow-wave sleep (SWS, the deeper non-REM sleep) and REM sleep are key to sharp, lasting recall of factual information, learned skills and abilities, and personal experiences. Whle SWS is thought to be the primary sleep phase for memory, REM, we’ve learned, pitches in, too. According to one study, for example, an enzyme activated during REM plays a key role in younger animals’ brain development, and the process of transforming experiences into multiple kinds of memories.

Also: Not-forgetting and remembering are distinct brain processes, and don’t forget it.

So many neural switches.

Neural Pathways Science Research 2015

How do our brains make us fall asleep or wake up? Which neurons light up to kick off, sustain or terminate new phases of sleep (REM, N-REM and their sub-phases)?

Brain scientists are tackling these questions, and a few research teams have identified “switches” — circuits, sometimes networks, of neurons — that, when activated or inhibited, perform a number of functions. To name a few, they cause near-immediate conking out or waking up, put the sleeping lab mice into REM states, pull them out of light N-REM sleep and shift their circadian clocks.

Getting a grasp on the neurophysiology underlying sleep is important to developing effective treatments for various sleep disorders. It’s also a huge undertaking.

Sleepers don’t become sneezers.

Sleep and the Immune System

Getting rest —  not too little, not too much — appears to enhance your chance of staying cold-and-flu free. One fascinating hypothesis, courtesy of German scientists, posits that the immune system needs deep sleep to encode memories of infections, so the body’s bodyguard system can recognize and fend off the same infections and similar ones in the future. (Remember: Vaccines are good.)

Meanwhile, another study told us that sleeping enough isn’t the only factor in staying in fighting shape. Timing matters, too. Scientists changed some mice over to a 20-hour (rather than 24-hour) schedule — they got enough sleep, just at different hours. The run-down rodents exhibited abnormal immune responses, suggesting a link between the vermin equivalent of shift work and vulnerability to infection.

We all have dreams. Not everyone remembers them.

Remembering Your Dreams

Sleep scientists from Paris realized that monitoring the rest of people diagnosed with REM Behavior Disorder (RBD), a sleep disorder in which people act out their dreams, would give them an entry point into determining whether self-professed non-dreamers are right. Alas, they’re — probably — wrong. Researchers observed them flail about during REM sleep, just like RBD patients who could remember their dreams.

Different parts of the brain can be awake and asleep at the same time.

Brain Regions

Traditionally, it’s been thought that the whole brain powers down as a single unit, but MIT neuro-geniuses discovered a neural circuit in the thalamic reticular nucleus that can put some brain regions to sleep without knocking out the whole thing.

Which, honestly, just makes us feel more tired.