What Goes On in the Brain When We Dream?

Bulkeley theorizes that dreaming “is the imagination at play, preparing for challenges, rehearsing, practicing things, exercising those capacities that help us thrive as a species,” he says. “It’s mental yoga. It keeps our minds flexible and adaptive.”

When do dreams happen?

Scientists believe that most dreams occur during REM, or the rapid eye movement stage of sleep. This is when your eyes move rapidly beneath closed lids, heart rate increases and your brain becomes highly active.

During REM, muscle tone shuts down — you essentially become paralyzed — which researchers think prevents you from physically acting out what you are dreaming. (Sleepwalking typically occurs during non-REM sleep.)

The first REM dream episode, running just 5 minutes or so, usually occurs about 90 minutes after falling asleep, De Koninck says. REM sessions happen every 90 minutes and become progressively longer as the night goes on. The second one runs about 15 to 20 minutes; you may have four or five depending on length of your sleep, he says. “In the morning, they last as long as 45 minutes, which is where we get the real long, elaborate dreams.”

Several parts of the brain ramp up or relax when we dream, Bulkeley says: 

• The prefrontal cortex quiets down. That’s the part of the brain where we process input from our surroundings and react to it. 
• The secondary visual processing center becomes more active. It’s located in the occipital lobe at the back of the brain and is where we form mental images.
• The limbic system, in the brain’s center, becomes more active. It is the site for emotions, instincts and memories.  

“The latest theory of how this all goes together is related to the default mode network” — a system of connected brain areas that become active when people are passive and not focused on the activities around them — “a fancy term for daydreaming,” Bulkeley says.

“The default mode network ties it all together,” he explains. “Dreaming is the activity of the default mode network while we sleep.” It’s like daydreaming, “although you have less control over the content, which becomes more emotionally and visually intense.”

Put another way: “When we dream, reasoning goes down, emotion goes up, secondary visual processing goes up, and they are all linked together by the default network,” he says. Scientists learn all this using an electroencephalogram, or EEG, during sleep to measure brain activity. To get a readout on dreams, they wake their subjects up during REM for immediate dream recall before the person forgets, De Koninck says. “When you wake up subjects during REM sleep …  their memory is more vivid” he says.

Dreaming changes as we age

Dreams about people or pets who have died “become more prominent when we get older,” Bulkeley says. “We dream about the dead coming back.”

As we age, dreams about being lost or losing things — like one’s keys — tend to increase, he adds, which “seems consistent with age-related changes in cognition and memory, but could be the emotional concern about cognitive changes, not necessarily cognitive changes themselves.”

Is there anyone who doesn’t dream? Again, scientists don’t know for sure. “If there are, it’s rare, maybe 1 percent or less,” Bulkeley says, pointing out that dream recall declines with age, which might cause people to think they no longer dream. “The vast majority of humans are dreaming regularly and remembering their dreams periodically.”

But there’s no harm in forgetting dreams. “Those who have rare or no dream recall lead normal lives,” Funkhouser says. “Those who remember their dreams, though, would miss them should they cease to remember them. They add color and depth to our lives.”

Haven’t you always wondered?

Do we dream in color — or in black and white?

Research suggests people who were around in the days of black-and-white television tend to dream in gray scale more than those who had no such exposure. Today, most dreams are in color, “although many dreams have no particular color that’s noticeable,” Bulkeley says. “I think of this question as a cultural response to The Wizard of Oz and its cinematic distinction between color and black and white as symbols of consciousness.”  

Do animals dream?

Scientists think they do, although we can’t wake up a sleeping dog or cat and ask. The next best thing: researchers’ studies of the brain activity in sleeping animals. “They have sleep cycles similar to ours, with cognitive activities in waking … that reappear in neural patterns in sleep,” Bulkeley says. Mice, for example, show similar brain waves when they are awake and learning to navigate a maze and when they are asleep, suggesting that “sleep and dreaming perform an information-processing function,” he says, at least in animals with the same basic sleep behaviors as ours.

Are my dreams like other people’s?

Who among us has not had the I-cut-classes-all-semester-and-now-I’m-facing-the final exam-unprepared (or showing up naked) dream? Other common ones include:

• Falling or getting lost
• Sex, often of a taboo nature
• Fleeing something that’s chasing you
• Flying — not in an airplane, but using your body
• Dead people visiting, as if alive

What’s this about knowing you’re dreaming while dreaming?

Some people do. It’s called “lucid dreaming.” The dreamer is aware the events are not real and may be able to control them — like directing their own personal movie — or wake themselves up. Some therapists use lucid dreaming to help people who’ve experienced trauma cope with recurrent nightmares, Bulkeley says.