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Women dreaming while sleeping.

Why do we dream when we sleep?

What causes dreams when we are sleeping?

“Why we dream and the function of our dreams has been the point of debate for many years,” says Jennifer Butler, M.D., a sleep medicine physician and pulmonologist at Piedmont. “The scientific community is split on the function of dreams and if they mean anything.”

Dr. Butler says there are many scientific theories for why we dream:

  • Activation-synthesis theory: Based on the work of Harvard University psychiatrists, this theory suggests dreams occur when there is stimulation in the brain that brings thoughts to our awareness. “Activation-synthesis hypothesis suggests dreams are caused by brainstem activation during rapid eye movement (REM) sleep and stimulation of the limbic system (emotional motor system),” she says.

  • Threat-simulation theory: Based on the work of a Finnish cognitive neuroscientist and psychologist, this theory suggests dreaming is preparation for real-life situations that may pose a threat.  

  • Biological response to life circumstances. “One researcher looked at why people have dreams with negative content, particularly dreams that involve attackers or enemies,” she says. “It could be an evolutionary and biological response, perhaps based on different life experiences.”

  • Organization of knowledge and memories. “Research published in 1985 suggests the purpose of dreams is to organize knowledge and to form brain connections, which helps with memory recall,” says Dr. Butler. “This theory suggests dreaming is an opportunity for the brain to problem-solve, make decisions and prioritize.”

Why are some dreams so strange?

“Research suggests dream content can be bizarre because the prefrontal cortex in the brain isn’t activated while we dream,” she says. “The prefrontal cortex is associated with higher-level reasoning. When that part of the brain isn’t activated, your mind doesn’t realize dream activities, like walking through walls, isn’t possible.”

When to see a doctor about your dreams

If you frequently have nightmares that impair your social, occupational, emotional or physical well-being, Dr. Butler recommends seeing your primary care physician or being referred to a sleep physician.

“Nightmares may be caused by stress, trauma or even certain medications, like beta blockers for high blood pressure or antidepressants,” she explains.

You should also see a doctor if you have symptoms of REM behavioral disorder.

“Normally, our motor functions are paralyzed during REM sleep, but with this disorder, people may act out violent dreams by punching, thrashing or kicking, which puts them and their bed partner at risk for injury,” says Dr. Butler. “This disorder has also been associated with Parkinson’s disease and symptoms can sometimes precede cognitive decline by a decade or more.”

Why do we remember our dreams some nights, but not others?

We have two sleep cycles:

  • Non-REM sleep, which occurs earlier in the night

  • REM sleep, which occurs in the latter part of the night and early morning hours

“If you wake up during REM sleep, you may be more likely to remember your dream’s content,” says Dr. Butler. “People also tend to remember dreams that have more negative content or negative emotions versus pleasant or benign content.”

How long does the average person dream each night?

“It’s hard to say,” she says. “We know we dream during our REM sleep cycles, which occur about every 90 minutes, but how much you dream can vary based on your age, medical conditions, medications and how many hours of sleep you get per night.”

Do dreams have any health benefits?

“Some researchers believe dreams prepare you for possible adverse events in real life, which may be considered a health benefit,” says Dr. Butler. “Others think dreaming may help with depression. The evidence is weak for whether dreams serve a true higher purpose or if they are just random. I look at dreams as a bridge between sleep and memory consolidation.”

Learn more about sleep and your health from Living Better experts.

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