[Below is the original script. But a few changes may have been made during the recording of this audio podcast.]

Are you sleeping well these days? You know, it's still amazing to me that experts haven't reached a consensus on what the exact purpose of sleep is.

One possibility is that it helps us build memory and problem solve.

In 1994 neuroscientists at the University of Arizona recorded the brain activity of rats as they navigated mazes and noted that specific brain cells (called "place cells") fired at specific spots along the route.

Then as the rats slumbered that night, scientists found the same cells firing, in the same order. The rat's brains were practicing running through the maze as they slept!

Researchers believe that the brain reactivates patterns of neural connections it made during the day—thus strengthening long-term memory during the night.

A 2005 fMRI study of pianists learning a complicated score found that they engaged different brain areas for the task, and that they performed better, only after snoozing.

During sleep, memory was specifically strengthened in the optimal brain areas for that task—those known to control hand movements. And these were different from the areas activated during the initial learning of the sequence.

Read about these and other sleep studies in the August/September issue of Scientific American MIND. Then, sleep on it.

—Christie Nicholson

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