When a person is not deliberately awaken they may not recall their dreams the next morning. Researchers discovered that dreams vary in length according to the length of the REM period. Because a dream seemed like a fleeting event individuals do not realize just how long their dreams can be. Non-REM sleep has four stages which equal about 75 percent of total sleep. In each stage, brain waves become progressively larger and slower, and sleep becomes deeper.
Sleep becomes progressively lighter until REM sleep, the most active period, occurs.
For most people this cycle occurs about once every 90 minutes. REM sleep begins in the pons, a structure in the brainstem, and neighboring midbrain regions. The pons sends signals to the thalamus and to the cerebral cortex, which is responsible for most thought processes. It also sends signals to turn off motor neurons in the spinal cord, causing a temporary paralysis that prevents movement. Why sleep is important Scientist discovered that about 70 million Americans have a sleep disorder.