Sunday, June 23, 2013

Sleep more. Period.

This post will be brief and ironic. Right now I am somewhere in Nebraska on a cross-country road trip from Ann Arbor to San Diego for my new job. So, while the message will be on the importance of sleep to your health, I will be loading up on caffeinated substances and sleeping very little to reach our destination. 

The content of this week's post is inspired by my undergraduate students at Michigan who consistently go through sleep deprivation exercises during the final weeks of each semester in order to pass their exams and get their papers in on time. What I am always reminding them is that losing sleep is the best way to assure that they won't retain the information they are studying. However, I have trained them so well that they have demanded evidence. So, here's a bit to start everyone off on the right track to appreciating: 

... why sleep is a critical part of the learning and memory process? 

In February of this year, Dr. Stickgold of Harvard Medical School and Dr. Walker of University of California-Berkeley published a review of the recent findings on sleep-dependent memory processes which have been a topic of interest for physiologists, psychologists and physicians since 1900 when sleep-related consolidation of memory was first published in a scientific journal. In these 113 years, combining information from rodent and human experiments of cellular and electrophysiological data, in nap paradigms and sleep deprivation programs, we have learned a great deal about when sleep facilitates memory. The consensus from these studies is that each day we learn and experience more than can be remembered. One of the important tasks our brain undertakes each day is sifting through all of these pieces of information (the weather, where you parked your car, the password to your bank account, etc.), and identifying what information is important to remember and what is necessary to forget. It appears that sleep plays a critical part in this job. 

We have learned this in simple paradigms where individuals are introduced to new information that is identified for them as "important to remember" or "important to forget." Participants in these studies are then randomized to either sleep for a number of hours or remain awake for a number of hours. The participants who slept remembered more information that was important, and forgot more of the information that was required of them to forget. Even more interesting, the participants who showed the best performance on these tasks also had faster sleep spindles while they were sleeping. This finding has been replicated a number of times as well as expanded to many different domains of information, such as emotionally relevant information. In short, if you will be tested on something, make sure you sleep well after you've learned it to assure optimal performance and retention. 

Going a step further, we also know that sleep plays a role in the integration of new information. For example, sleep helps us learn a set of information and then extrapolate general rules from that information (e.g., grammar rules from reading sentences), navigation (e.g., learning a virtual maze when introduced through different starting points), and acquiring new vocabulary (e.g., taking a new class or learning a new language). All of these are just a few examples of the experiments that have been conducted to test what areas of learning and memory are benefitted uniquely by sleep. 

Unfortunately, it's important to keep in mind that we still have a great deal to learn about the chemical and physiological processes that allow information to be selectively retained and integrated through sleep. While there are a number of behavioral interventions that are very effective for managing and improving sleep, we are far from targeted physiological interventions that enhance these learning processes. 

Now, we all nod our heads in agreement when people say, "Sleep is important," but in practice there is always something that seems to be a good enough reason to lose sleep. Very often when I decide to see the midnight release of a new film, or just stay up to finish revisions on a paper, I only consider feeling tired the next day as a potential negative consequence, which couldn't be further from the truth. The real consequences last much longer. 

The last decade of research suggests that sleep is just as important as diet and exercise to good health, partially because sleep facilitates or impedes the health benefits of the other two, but also because sleep is responsible for important restorative processes. When we experience the deepest stages of sleep, hormones are released which restore our brains, hearts, and kidneys. When we deprive ourselves of sleep, the number of times we reach these deep stages of sleep is reduced, and our brains, kidneys, and hearts are the victims. What's even more frightening, the physiological damages of depriving your body and mind of these restorative periods during sleep (called "sleep debt" by researchers), become irreversible if the "debt" gets too large. 

The moral of the story: think twice about losing sleep. The consequence is that you will live a shorter life that you won't remember well. How do you do that? As a psychologist, I'm a firm believer in keeping track. You should be sleeping at least 3, but ideally 4 sleep cycles each night. There are a number of new technologies that can help you learn more about how you are sleeping, how long your cycles are, how long it takes you to fall asleep, and when you need to catch up on some restorative ZZZs. On the expensive side I've used the ZEO Sleep Machine ( ), was an early-adopter of the FitBit ( ), but also use the Sleep Time app on my iPhone which are all great options. As always, knowing is half the battle, but it's also helpful to consult the basic rules of Sleep Hygiene which can be found conveniently on Wikipedia ( ). Sweet dreams!  

Stickgold, R., & Walker, M. P. (2013). Sleep-dependent memory triage: evolving generalization through selective processing. Nature neuroscience,16(2), 139-145.

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