You think when you go to sleep, you just, well, sleep?

Sleep, as it turns out, is far more complicated than we thought. And the brain not only doesn’t turn off, but appears to help keep itself healthy.

We’ve all heard of REM — rapid eye movement — discovered by the late physiologists Eugene Aserinsky and Nathaniel Kleitman at the University of Chicago in 1953. Scientific American has the story:

During REM sleep, our brain waves—the oscillating electromagnetic signals that result from large-scale brain activity—look similar to those produced while we are awake. And in subsequent decades, the late Mircea Steriade of Laval University in Quebec and other neuroscientists discovered that individual collections of neurons were independently firing in between these REM phases, during periods known as slow-wave sleep, when large populations of brain cells fire synchronously in a steady rhythm of one to four beats each second. So it became clear that the sleeping brain was not merely “resting,” either in REM sleep or in slow-wave sleep. Sleep was doing something different. Something active.

Discovering REM sleep was the first clue that sleep didn’t just help keep our bodies healthy, but our minds as well. And while many studies have been conducted on sleep since 1953, it’s only been in the last decade where we’ve begun to appreciate the complexity and importance of sleep for our minds. In 2000, researchers discovered that people that received more than 6 hours of sleep during an experiment helped improve their performance on tasks designed to tax the memory.

The key came in the discovery that participants didn’t just require REM sleep to improve their performance — they needed all that other sleep time too (what scientists call ‘slow-wave’ sleep).

The long article also provides a nice description of our current understanding of how memory works:

To understand how that could be so, it helps to review a few memory basics. When we “encode” information in our brain, the newly minted memory is actually just beginning a long journey during which it will be stabilized, enhanced and qualitatively altered, until it bears only faint resemblance to its original form. Over the first few hours, a memory can become more stable, resistant to interference from competing memories. But over longer periods, the brain seems to decide what is important to remember and what is not—and a detailed memory evolves into something more like a story.

The researchers also discovered that sleep helps stabilize memories — sleep changes our memory, “making it robust and more resistant to interference in the coming day,” as the article notes.

But wait, sleep does more! It may not just stabilize our memories, it may actually help our brains process the memories, keeping the bits we need for long-term memories (especially the emotional components), and dropping the extraneous details that would clog our limited storage capacity:

Over just the past few years, a number of studies have demonstrated the sophistication of the memory processing that happens during slumber. In fact, it appears that as we sleep, the brain might even be dissecting our memories and retaining only the most salient details. […] Instead of deteriorating, memories for the emotional objects actually seemed to improve by a few percent overnight, showing about a 15 percent improvement relative to the deteriorating backgrounds. After a few more nights, one could imagine that little but the emotional objects would be left. We know this culling happens over time with real-life events, but now it appears that sleep may play a crucial role in this evolution of emotional memories.

But wait, sleep does even more!

Even more recent research suggests that sleep helps our brain to process the information of the day and solve problems.

The upshot is that sleep is far, far more important than most of us realize and few of us appreciate. We miss it and think nothing of chopping off a few hours here or there. But the emerging research suggests that when we cut out sleep, we may be actually harming our formation of new memories for the recent past, and our ability to perform up to our usual standards. The researchers sum it up best:

As exciting findings such as these come in more and more rapidly, we are becoming sure of one thing: while we sleep, our brain is anything but inactive. It is now clear that sleep can consolidate memories by enhancing and stabilizing them and by finding patterns within studied material even when we do not know that patterns might be there. It is also obvious that skimping on sleep stymies these crucial cognitive processes: some aspects of memory consolidation only happen with more than six hours of sleep. Miss a night, and the day’s memories might be compromised—an unsettling thought in our fast-paced, sleep-deprived society.

Read the full (albeit long) article at Scientific American: Sleep on It: How Snoozing Makes You Smarter

While You Sleep, Your Brain Keeps Working