Why Do We Dream? A Sleep Expert Answers 5 Questions

What sleep experts know — and don't know

Your brain splices both strange and familiar scenarios together to create the weirdest midnight movies ever. So what’s going on when you dream — and what does it all mean? We’ve asked sleep medicine expert Michelle Drerup, PsyD, to answer five questions about dreams:

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1. How do dreams happen?

Most dreaming occurs during REM (rapid eye movement) sleep, which we cycle through periodically during the night. Sleep studies show our brainwaves are almost as active during REM cycles as they are when we’re awake.

Experts believe the brainstem generates REM sleep and the forebrain generates dreams. Why? Because if the brainstem is injured, patients dream but don’t go into REM sleep. And if the forebrain is injured, patients go into REM sleep but don’t dream.

Other things that happen during REM sleep include:

  1. You lose muscle tone so that you don’t act out your dreams and hurt yourself. (This protection is missing in REM sleep behavior disorder.)
  2. You can’t regulate temperature by sweating or shivering, so your body temperatures drift toward the temperatures of your room.
  3. Your breathing and heart rate become irregular, so if you have sleep apnea, it is more prominent during REM sleep.
  4. Your pupil constricts, possibly serving to protect your eyes if you’re exposed to brighter light.

2. Why do dreams seem so bizarre?

This may have to do with neurotransmitters, or brain chemicals. Some are more pronounced, while others are suppressed, during REM sleep.

Acetylcholine (which maintains brain activation) is more prominent, as is dopamine (which some researchers link to hallucinations). Dopamine may help to give dreams their surreal quality.

The relationship between space and time also changes when we dream. Time may seem to last forever — or pass by very quickly.

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Meanwhile, REM sleep suppresses the neurotransmitters that usually keep us awake: histamine, serotonin and norepinephrine. Thus, we’re less conscious of our environment.

Some researchers suspect the thalamus (the gateway for sensory input) closes when we dream.

3. Is dreaming good for you?

That’s where the jury is out. The prevailing theory is that dreaming helps us consolidate and analyze our memories (like skills and habits) and helps us with priming (our ability to respond in a certain way).

But some experts disagree. And don’t yet have detailed knowledge about how this happens.

4. Do dreams mean anything?

That’s up for debate. In the 1950s, Freud introduced dream interpretation, but we have never been able to substantiate his claims.

We do know that people with post-traumatic stress syndrome (PTSD) are more likely to have nightmares. So dreaming can accompany psychiatric conditions. Yet normal people have nightmares, too, so opinions are divided.

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5. How are dreams created?

One study suggests that dreams stem more from your imagination (the memories, abstract thoughts and wishes pumped up from deep within your brain) than from perception (the vivid sensory experiences you collect in your forebrain).

But there is so much more to discover. We know much — but not all — of what’s going on physiologically during dreams. We have far more to learn about what’s going on psychologically.

For example, we know that nightmares are a manifestation of tension for people with PTSD, because they recur around their traumatic experience. For others, are dreams related to good moods or bad moods?

We can’t answer this easily because we have not found a good way to study dreams in people. Memories of dreams fade quickly after you wake up, and it’s difficult to correlate brain scans with patients’ reports of their dreams.

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