Resource: The Function of Sleep

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Whether you're a student or a business professional, society puts a high importance on learning and the ability to remember what we've learned so that we might apply it in our lives. Without memory, we would not be able to apply new information. For the rats being studied in this video, good memory can translate into gaining a reward for completing a task. For humans, it can be the difference between passing or failing an exam or being able to perform a job. As this video suggests, sleep may determine our capacity to recall what we learn.

Learning and memory have three main components: acquisition, the introduction of new information into the brain; consolidation, the processes by which a memory becomes stable; and recall, the ability to access the information after it has been stored. Each of these steps is necessary for proper memory function. While acquisition and recall occur while we're awake, research suggests that consolidation occurs during sleep.

Human brains have evolved in such a way that different parts are responsible for controlling these different functions. The hippocampus is considered the control center responsible for processing memories. The memories themselves are stored away in different areas of the cerebral cortex, the large outermost part of the brain. To help determine sleep's role in connecting learning and memory, scientists monitor brain wave activity in the hippocampus and cerebral cortex as we cycle through various stages of sleep during the night.

In each stage, distinct high-voltage or low-voltage activity patterns are recorded on the monitors. Sleep researchers attempt to interpret what effects these stages have on memory. They have found that sleep helps improve some kinds of memory tasks more than others, including recognition of visual patterns, solving puzzles, and learned skills such as typing. Moreover, different stages appear to help consolidate different kinds of memories.

For example, rapid-eye movement (REM) sleep seems to play a role in the consolidation of procedural, or "how-to," memory. This is the stage of sleep in which dreaming occurs most frequently. In the non-REM sleep stages, the bursts of high-frequency neuronal activity that are characteristic of stage 2 sleep, in which adults spend about half their sleep time, may modify neural connections and enhance memories. Also, the slow-wave sleep that characterizes "deep sleep" (stage 3 sleep) might be connected to spatial memories. When rats in this video ran the maze and then replayed the memories as they slept, the neuron firing patterns recorded in the hippocampus appeared in slow-wave sleep, precisely matching those recorded when the rats ran the maze when awake.

Some scientists believe that the same thing happens when we sleep. However, when we are sleep-deprived, our attention drifts. Our over-worked neurons can no longer function to coordinate information so that memories are properly consolidated. Thus, we lose our ability to access previously learned information.

To learn more about sleep and its effect on brain function, check out The Teenage Brain.

To learn more about brain anatomy and function, check out Brain Geography or Growing Up with Epilepsy: Brain Anatomy and Development.

To learn more about the different stages of sleep, check out Natural Patterns of Sleep.

Practice a procedural skill in this NOVA scienceNOW classroom activity to investigate the effects of sleep on learning and memory.

Print Questions for Discussion

• What question is the scientist in this video trying to answer?
• What data or clues does he have to support his idea?
• How are a rat's thoughts mapped? What happens to a rat's thoughts when it falls asleep?
• What conclusions, if any, can the scientist make about the relationship between sleep and memory?