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Rat Sleep

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Ancient people believed dreams were prophecies. Sigmund Freud believed that dreams reveal our secret fears and desires. Today, researchers are creating and analyzing detailed charts of the brain's electrical activity during dreaming. And they're becoming convinced that the true purpose of dreaming is learning. You'll hear more in this Science Update.


Transcript

Do dreams helps us learn? I'm Bob Hirshon and this is Science Update.

The hippocampus is a tiny brain structure that helps us navigate and form memories. At MIT, neurophysiologist Matthew Wilson charts the activity of the hippocampus in rats, while they learn to run a maze. On these charts, you can actually see every step the rats took, and even tell if they were walking or running. Wilson then measured the rats' brain activity while they slept, and found that they replayed their journey through the maze in their dreams.

Wilson:

The activity is so reliable, it's so consistent and literally allows you to estimate the location of the animal on a second by second basis.

This suggests that dreams are a way of sorting through the day's activities, replaying and reinforcing important sequences. In other words, that dreams help us learn. Today, at the annual meeting of the American Association for the Advancement of Science, Wilson describes his latest efforts to see what other parts of the brain are involved.

Wilson:

Is it seeing what it saw when it ran? Is it experiencing the footfalls as it moved through the maze? Is it experiencing the emotions? All of these things are questions that we're studying at the moment.

The answers could help the researchers understand how dreams affect what we learn and remember. For the American Association for the Advancement of Science, I'm Bob Hirshon.


Making Sense of the Research

This is one of many scientific investigations probing the role of sleep as a powerful learning tool. Over the past decade, a great deal of evidence has accumulated suggesting that sleep, especially the deep phase of sleep called REM (when your eyes dart back and forth), plays a role in learning. For example, human subjects learning a new physical skill improve more quickly when they can sleep in between practice sessions.

In this study, the researchers are taking a closer look at the sleep-learning connection by zeroing in on the cells of the rat hippocampus. As the center for spatial learning, the hippocampus is an ideal target for study, because cells in this part of the brain fire in patterns that directly correspond to the spatial task being learned. This doesn't mean that you can hook a rat's brain up to a monitor and see an exact mirror image of the maze it's learning. But it does mean that the cells fire in a specific pattern that matches up with the changes in the position of the rat's head in space. The result is kind of like a code that tracks the rat's movements, which can be translated and monitored during both learning and sleeping.

The key here is that when a rat falls into REM sleep after working on a maze, the cells in its hippocampus repeat the same patterns over again, like a tape being replayed. For reasons not yet known, the replay happens a little slower than real-life learning, but the sequence of cells firing is exactly the same. This lends more support to the theory that REM sleep helps organize, solidify, and cement things that you've just learned. (If this theory is correct, then all-night cram sessions may not be as effective as moderate studying followed by a good night's sleep.)

This study opens up many more intriguing questions than it answers. For example, what exactly is going on inside a rat's head while it sleeps? How do these patterns manifest themselves as dreams? Are they literal replays of what they experienced earlier in the day, or are they more abstract, as many human dreams can be? How are mistakes treated in the dreams? Are they "corrected"? Can dreams suggest new ways of getting through the maze that are acted upon the next day? And what role does the rest of the brain play in all of this? The researchers are planning and conducting new studies that might provide clues to some of these mysteries.

Now try and answer these questions:

  1. What role is REM sleep believed to play in learning?
  2. Why did the researchers choose to study the hippocampus, and not some other area of the brain?
  3. Describe what happens to the cells in the hippocampus during learning and sleeping.
  4. Suppose the researchers wanted to see how important sounds are processed in the brain during learning. How could they add to the experiment described here, in order to begin to answer this question?
  5. Why is it important to understand dreaming? Give examples of how this research could eventually prove beneficial beyond the academic world.

For Educators

The PBS Documentary From Zzzzz’s to A’s explores the relationship between sleep and learning in adolescents.

SleepNet.com is a non-commercial site devoted to education about sleep and sleep disorders.

The National Sleep Foundation has a website containing information, links, a "Caffeine Calculator," and a "Sleep IQ" test.


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