Everybody's doing it! Dogs do it; rats do it; sheep do it; there's even evidence that fruit flies do something like it. We do it too, and we do it a lot...

Sleep.

Humans sleep for roughly eight hours every day. That means that a human who lives to be seventy-five years old will have spent twenty-five of those years in a seemingly unconscious state. Twenty-five years! But all this sleeping is not wasted time; we need to get lots of sleep. Consider this: if you sleep deprive a rat for too long, the rat will die! This tells us that sleep is a very important need. Interestingly, though, we still don't really know why.

Did You Know?
By the age of 75, you will have spent approximately 25 years sleeping...that is roughly 1/3 of your life.

Currently, there are many theories revolving around our need to sleep, but none have adequately explained the phenomenon that dominates our nights. We can classify sleep into different stages, based on electroencephalographic (EEG) recordings. EEGs are used by clinicians and researchers to, amongst other things, study sleep. They measure electrical activity in the brain and different stages of brain activity are characterized by waves that differ in amplitude and frequency. Figure 2 shows the relationship between EEG recordings and sleep stages.

Did You Know?
EEGs measure electrical activity in the brain. Electrodes are attached to different parts of the head to detect these "brainwaves".

Now that summer is over and you are back in school, what does sleep have to do with learning, studying, and the inevitable exams that you will have to write?

Well, one theory for why we need sleep is that the sleep helps us to process information and even to store it as memory. Just as there are different stages of sleep, there are also different kinds of memory, some of which appear to be more or less affected by a lack of sleep.

Did You Know?
Your brain processes the information that it has gathered during the day while you sleep. A lot of the information gets committed to memory during this time.

There are variable reports, for instance, regarding the necessity of a good night's sleep with respect to declarative memory (i.e. the ability to remember facts and events). Some researchers have found that a full night's sleep is critical for forming declarative memories, while others have found that mild sleep deprivation has no effect. It is possible that the difficulty of the task being performed and the emotional relevance of the information strongly influenced the outcome of these studies and, therefore, led to the varying results. The discrepancy between these results indicates that scientists still need to conduct a lot of research examining the effects of sleep deprivation on declarative memory.

Did You Know: Declarative memory refers to our ability to remember facts and events. Procedural memory refers to our knowledge of how to do things.

However, the necessity of sleep for consolidating procedural memory seems to be much more clearly established. Procedural memory (i.e., our knowledge of how to do things such as playing the piano or learning to swim) has been shown to be very dependent on a good night's sleep. One way to investigate this is to teach a subject a task and then to test them on the task several hours later. During those several hours, the subject either gets to sleep or is sleep deprived. Regardless of the type of procedural memory being tested (e.g. motor learning tasks, visual discrimination tasks, pitch memory tasks), the subjects that are allowed to sleep perform significantly better than the subjects that are sleep deprived.

Did You Know?
Studies show that sleep deprivation prevents us from remembering how to doing things properly.

Collectively, these studies suggest that getting your ZZZZZs will be of great benefit when you are studying for a test. But wait! There's more...

It's important to consider your overall functioning, not just whether or not you can remember the name of Canada's 7th Prime Minister. Studies have shown that sleep deprivation can impair your performance at a simulated driving task just as much as if you had a blood alcohol concentration of 0.08%, the national legal limit (CRAM NOTE: For more on Blood Alcolol Levels, see "Don't Hold Your Breath"). So, if you don't get enough sleep you are not only jeopardizing your ability to remember, but you are also likely to experience impaired physical function.

Did You Know?
Cramming for exams is not the best way to study! You need the proper amount of sleep for two reasons: 1) to process the information you have reviewed, and 2) to ensure that you performance is not impaired.

How much sleep do you actually need?

Studies have indicated that teenagers require at least 9 hours of sleep per night (but often get much less). Try listening to your body — are you tired? Do you feel refreshed in the morning?

Overall, there has been a considerable amount of research indicating that mammals perform better at learning and memory tasks after a good night's sleep. And, while scientists still have yet to figure out conclusively why we need to sleep, there can be little doubt that sleep is in fact a basic biological need. It's a natural and substance-free way to increase performance and to feel good!

P.S. Canada's 7th Prime Minister was Sir Charles Tupper

References

Arnedt JT, Wilde GJS Munt PW MacLean AW (2001) How do prolonged wakefulness and alcohol compare in the decrements they produce on a simulated driving task? Accident Analysis & Prevention, 33, 337-344.

Everson CA, Bergmann BM, Rechtschaffen A (1989) Sleep deprivation in the rat: III. Total sleep deprivation. Sleep, 12, 13-21.

Health Canada: Be Drug Wise - Questions and Answers:

http://www.drugwise-droguesoisfute.hc-sc.gc.ca/needhelp-besoinaide/questions_e.asp

Hendricks JC, Finn SM, Panckeri KA, Chavkin J, Williams JA, Sehgal A, and Pack A. I. (2000) Rest in Drosophila is a sleep-like state. Neuron 25, 129—138.

How Stuff Works: http://static.howstuffworks.com/gif/sleep-stages.gif

Kandel ER, Schwartz JH, and Jessel TM (Eds.) Principles of neural science (4th Ed.) McGraw-Hill: United States (2000) pp 897-900.

National Sleep Foundation: http://www.sleepfoundation.org/

SouthCoastToday.COM: http://www.southcoasttoday.com/daily/03-06/03-28-06/01fiveminute.htm

Walker MP & Stickgold R (2006) Sleep, memory, and plasticity. Annual Review of Psychology, 57:139-166.

For more information about sleep-need and performance:

Canadian Sleep Society:

http://www.css.to/

National Sleep Foundation:

http://www.sleepfoundation.org/

Sleep Research Society:

http://www.sleepresearchsociety.org/

Michelle Black received her BSc from Nipissing University (North Bay, ON) and is now pursuing a PhD at Dalhousie University (Halifax, NS). Her research is focuses on the brain mechanisms of sleep and arousal. She is a big fan of both studying and engaging in sleep.

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