By Jeanna Bryner
LiveScience

When your head hits the pillow, for many it's lights out for the conscious part of you. But the cells firing in your brain are very much awake, sparking enough energy to produce the sometimes vivid and sometimes downright haunted dreams that take place during the rapid-eye-movement stage of your sleep.

Why do some people have nightmares while others really spend their nights in bliss? Like sleep, dreams are mysterious phenomena. But as scientists are able to probe deeper into our minds, they are finding some of those answers.

Here's some of what we know about what goes on in dreamland.

1. Violent dreams can be a warning sign

As if nightmares weren't bad enough, a rare sleep disorder — called REM sleep behavior disorder — causes people to act out their dreams, sometimes with violent thrashes, kicks and screams. Such violent dreams may be an early sign of brain disorders down the line, including Parkinson's disease and dementia, according to research published online July 28, 2010, in the journal Neurology. The results suggest the incipient stages of these neurodegenerative disorders might begin decades before a person, or doctor, knows it.

2. Night owls have more nightmares

Staying up late has its perks, but whimsical dreaming is not one of them. Research published in 2011 in the journal Sleep and Biological Rhythms, revealed that night owls are more likely than their early-bird counterparts to experience nightmares.

In the study 264 university students rated how often they experienced nightmares on a scale from 0 to 4, never to always, respectively. The stay-up-late types scored, on average, a 2.10, compared with the morning types who averaged a 1.23. The researchers said the difference was a significant one, however, they aren’t sure what's causing a link between sleep habits and nightmares. Among their ideas is the stress hormone cortisol, which peaks in the morning right before we wake up, a time when people are more prone to be in REM, or dream, sleep. If you’re still sleeping at that time, the cortisol rise could trigger vivid dreams or nightmares, the researchers speculate. [ Top 10 Spooky Sleep Disorders ]

3. Men dream about sex

As in their wake hours, men also dream about sex more than women do. And comparing notes in the morning may not be a turn-on for either guys or gals, as women are more likely to have experienced nightmares, suggests doctoral research reported in 2009 by psychologist Jennie Parker of the University of the West of England.

She found women's dreams/nightmares could be grouped into three categories: fearful dreams (being chased or having their life threatened); dreams involving the loss of a loved one; or confused dreams.

4. You can control your dreams

If you're interested in lucid dreaming, you may want to take up video gaming. The link? Both represent alternate realities, said Jayne Gackenbach, a psychologist at Grant MacEwan University in Canada.

"If you're spending hours a day in a virtual reality, if nothing else it's practice," Gackenbach told LiveScience in 2010. "Gamers are used to controlling their game environments, so that can translate into dreams." Her past research has shown that people who frequently play video games are more likely than non-gamers to have lucid dreams where they view themselves from outside their bodies; they were also better able to influence their dream worlds, as if controlling a video-game character.

That level of control may also help gamers turn a bloodcurdling nightmare into a carefree dream, she found in a 2008 study. This ability could help war veterans suffering from post-traumatic stress disorder (PTSD), Gackenbach reasoned.

5. Why we dream

Scientists have long wondered why we dream, with answers ranging from Sigmund Freud's idea that dreams fulfill our wishes to the speculation that these wistful journeys are just a side effect of rapid-eye-movement (REM) sleep. Turns out, at least part of the reason may be critical thinking, suggests Harvard psychologist Deirdre Barrett who presented her theory in 2010 at the Association for Psychological Science meeting in Boston.

Her research revealed that our slumbering hours may help us solve puzzles that have plagued us during daylight hours. The visual and often illogical aspects of dreams make them perfect for the out-of-the-box thinking that is necessary to solve some problems, she speculates.

So while dreams may have originally evolved for another purpose, they have likely been refined over time for multiple tasks, including helping the brain reboot and helping us solve problems, she said.

What's the strangest dream you remember? Tell us on Facebook

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Dreams can serve as your brain's personal psychotherapist by helping process bad memories, experts say.

Ever since the dawn of humanity, people have wondered about the purpose of dreams. We’ve imbued these mental meanderings with all sorts of powers, from forecasting the future to providing a window into the soul.

But scientists say they now know what dreams are for: they sooth the sting out of troubling memories. And when dreams don’t do their job, horrific memories can take over a person’s life, as they do with PTSD, a new study suggests.

Matthew Walker and colleagues at the University of California, Berkeley, found that the brain uses dreams to strip the emotional content from memories of painful events.

Here’s how the researchers think it works. During dream, or REM, sleep, our brain chemistry changes, leaving us with lower levels of stress hormones. While we’re in this quieter state, the brain mulls over what happened and then files away the memory – but with less emotion attached.

 So, when everything works right, when we later recall these events we’ll remember what happened, but less of the pain associated with them.

Walker and his colleagues tested their theory in an intriguing, but simple, experiment.

The researchers asked 35 healthy volunteers to lie in a brain scanner while looking through a series of 150 images, which ranged from bland to emotionally jarring. One image might show a tea kettle, for example, while another might show the aftermath of a horrific car accident. As they were looking at the images, the volunteers were asked to rate the emotional intensity of what they were viewing.

Half the volunteers looked at the images in the morning, while the other half looked at the images just before bedtime. Twelve hours later the volunteers were asked once again to look at and to rate the images while being scanned. This meant that half the volunteers had a night’s sleep in between scans.

What the second set of scans and ratings showed was telling. Volunteers who had slept through the night rated the horrific photos as far less emotionally charged – and their brain scans showed a much lower level of activity in the amygdala, a brain region central to emotional processing.

It’s like dreams become the brain’s psychotherapist, Walker explains. Just as we can benefit from reviewing disturbing events in the safety of a therapist’s office, our brain benefits from processing these same types of events in the quieter dream state.

Walker suspects that the system short-circuits in PTSD sufferers because their brains are  constantly charged up even during dreams. And research in veterans with PTSD appears to bear this out, Walker says. When veterans with PTSD are given medications that knock back a neurotransmitter that keeps the brain in an excited state, sleep appears to improve symptoms of the disorder.

 “We’re hoping to provide the mechanism by which that drug has its effect,” Walker says.  

What types of things do you dream about? Tell us on Facebook.

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