Long TextExercise 69 of 83

We spend roughly a third of our lives asleep, yet for centuries the purpose of sleep remained one of the most stubborn mysteries in biology. It was long assumed that sleep was essentially a period of inactivity - the body's way of conserving energy when there was nothing useful to be done. This view persisted well…

• What was the traditional view of sleep that persisted for a long time?
• Why was the discovery of REM sleep so significant?