What causes dreams?
Scientists don’t know yet what causes dreams, but we do know something about the state of dreaming.
Immediately after we go to sleep, our brains enter a stage called ’slow wave’ sleep. The brain waves (electrical activity in the scalp) slow down distinctly from the awake stage, the muscles are completely relaxed, and the heart beat, blood pressure, and body temperature reduce. If someone is woken up at this stage, they don’t remember dreams.
Then the brain waves change: as we enter what is known as ‘rapid eye movement’ (REM) sleep, the brain waves are indistinguishable from when we are awake. This is when we dream.
When we dream, our heart rate and blood pressure may rise, and the eyes move behind the eyelids (hence the term REM sleep). The rest of the muscles, though, are in a state of paralysis (except for those that control the basic body processes). This is what prevents us from acting out our dreams.
Normally, slow-wave sleep alternates with REM sleep. Over one night of sleep for the normal adult, the REM sleep stages become gradually longer till the person awakens. Babies, though, spend much of their sleep in slow-wave sleep.
When the switch between slow-wave sleep and REM sleep does not work properly, it can cause a lot of trouble. In people who walk or talk in their sleep the mechanism that causes low muscle tone during REM sleep doesn’t seem to switch on. On the other hand, in people with narcolepsy, the muscles may suddenly lose tone (like during REM sleep) when the person is awake. The person will not be able to move – a state called cataplexy. People with narcolepsy also switch between the waking and sleeping states suddenly (they may have a sleep attack in the middle of a cooking or driving, for example) as well as between slow-wave and REM sleep.
Why? Scientists suspect that a mixture of genetics and environmental factors cause narcolepsy. But like so many things connected with sleep, we don’t understand much about what is the trigger.