Psychology › Section D · States of consciousness › Topic D.2
Sleep and why we sleep
We spend roughly a third of our lives - some 25 years of them - asleep, and rats kept from sleeping die within weeks. Yet after a century of research, no single theory fully explains why. This topic covers what sleep is and the major hypotheses for its purpose, each with its evidence honestly weighed.
In this topic
- A third of life, and nonnegotiable
- What sleep is
- Hypothesis 1: energy restoration
- Hypothesis 2: adaptive predator avoidance
- Hypothesis 3: the brain's housekeeping
- The honest verdict
- Worked example: weighing the energy hypothesis
- Worked example: sleep rebound - the homeostatic read
- Common mistakes to avoid
- Key takeaways
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