“There is a mild sleep deprivation in the entire world.” – Michael Rosbash, Nobel Prize in Physiology or Medicine 2017

Sleeping is a strange thing we all do every single day. It’s strange because when you think about it, we spend close to a third of our lives asleep, and while we’re sleeping, we’re vulnerable—and, at least on the outside, fully unproductive. For a long time, scientists have been amused by sleep’s apparent uselessness; some even quip that the only known function of sleep was to cure sleepiness. In a 2006 scientific survey on the probable functions of sleep, Marcos Frank, a neuroscientist, then working at the University of Pennsylvania, concluded that the evidence for sleep’s putative effects on cognition was “weak or equivocal.” That has not stopped researchers from probing into the mystery of sleep and in the past decade, some progress has been made to clear the air.

Sleep and Physical Health

After a good night’s sleep, most of us feel restful and calm, more ready to take on what comes during the day than if we are sleep deprived. This suggests that sleep may be highly beneficial to our physical well-being. Formal scientific studies corroborate this intuition. In one study to test the relationship between sleep and cardiac health, a group of physiologists subjected healthy men with no history of cardiac problems to sleep deprivation. At various points, they measured their blood pressure, and their levels of specific proteins associated with heart problems. Within two days, almost every marker was elevated, indicating that lack of sleep over a long period of time may impair critical aspects of our physical health.

Sleep and Mental Health

While asleep, we also dream. Do dreams have anything to do with memories? If so, why recall bits and pieces of memories that are haphazard and apparently serve no purpose? About 25 years ago, Richard Stickgold, a professor of psychiatry at Harvard Medical School conducted research which has become one of the most convincing validations of the role that sleep and dream play in memory consolidation. For seven hours over the course of three days, a group of people played a computer game called Tetris that involves arranging a small sequence of shapes into complete lines. Some had never played the game before; others were familiar with it, and a third group were amnesiacs with extensive damage to their medial temporal lobes and hippocampi, two regions of the brain which have been implicated in studies of memory. Due to their medical condition, this group didn’t know whether they were familiar or not with the game.

Each night, the subjects were repeatedly awoken as they were falling asleep and asked to recall what they were dreaming about. It turned out that they dreamt of Tetris. The most interesting finding was that even the amnesiacs had these dreams. The next morning, they could recall falling shapes that conformed to the Tetris patterns. Sometimes, they would even report that the shapes rotated to fit into rows. Reviewing that study and parallel advances by other researchers, Stickgold argued that sleep isn’t just crucial for memory consolidation; it is also a remarkable mechanism for sifting through tons of memories we hold in our heads and storing the important bits, what he calls the “gist” or overarching point or a specific detail.

In a separate study conducted by University of Tubingen neurobiologist, Jan Born and Ullrich Wagner, a neuroscientist at the University of Munster, a group of people were taught a difficult math problem. Though the subjects didn’t know it, there was a simpler way to solve the problem – an abstract rule that gives a quick solution. Few of the subjects figured out the solution the first time. Each subject was retested on the task eight hours later; some were allowed to sleep and others had to remain awake. Of those who stayed awake, only a quarter came up with the faster solution. But the insight rate more than doubled among the subjects who had spent the eight hours sleeping (63% could now see the shortcut).

I can relate to this study because as a senior undergraduate in economics, I was given a technically challenging thesis topic to write, and which I had to pass in order to graduate. It involved quite a bit of math (mostly systems of differential equations) to model some aspects of the economy. A week before the thesis was due, I was still struggling to solve the main puzzle but by that time, I was so mentally exhausted that I literally dozed off in the university library. I cannot recall how long I slept, but I remember vividly that when I woke up, I could “see” strong hints of the solution running through my head. Working feverishly, I completed the thesis in short order, ran over to my supervisor for checks and lo and behold, she said that I’ve nailed it. To this day, I still get goosebumps whenever I recall this uncanny event. Did the time I spent sleeping help me save the day? I have no doubt it did.

Scientists around the world are not letting up on their research to better understanding the myriad functions of sleep. From what we know so far, sleep plays a pivotal role in maintaining both our physical and mental health. When we’re awake, our blood pressure and heart rates are naturally more elevated to keep us moving through the activities of the day. These markers “take a break” as it were as we enjoy a good night’s sleep. Similarly, when we’re awake, our activities lead to a build-up of debris in the brain in the form of toxins such as beta-amyloid, a protein infamously linked to Alzheimer’s disease. When we fall asleep, specific channels in our brain expand, allowing cerebrospinal fluid to flow in to clear those debris. This mechanism is termed the “glymphatic system,” a nod to the lymphatic system that clears waste from our bodies. This means that if we are sleep-deprived (having less than at 7 hours of uninterrupted sleep each day), our brains don’t get enough rest, toxins build up in the brain which has the scary potential to trigger all sorts of neurodegenerative diseases.

Notes and Further Reading

[1] The research by Stickgold mentioned above can be found in the following reference:

Robert Stickgold, April Malia, Denise Maguire, David Roddenberry, and Magaret O’Conner (2000), “Replaying the Game: Hypnagogic Images in Normals and Amnesics,” Science, 290: 5490.

[2] Parts of today’s post have been adapted from Maria Konnikova, ‘The Work We Do While We Sleep’, published in The New Yorker, July 8, 2015.