Whether we're falling or flying, dancing or driving, moving in our dreams feels very real to us at the time. And our brains, it seems, agree. By imaging the brains of sleeping subjects, researchers have found that when we move in our dreams, our brains fire in the same pattern as when we move in the real world.
Because we tend to forget our dreams as soon as we wake up, researchers know little about how our minds create them. Neuroscientists Martin Dresler and Michael Czisch, both of the Max Planck Institute of Psychiatry in Munich, Germany, and their colleagues wanted to find a way to use brain-imaging techniques to watch what people were doing in their dreams. To interpret these images of the dreaming brain, however, they would first have to know how the brain looks when it is performing a certain task in the dream—a difficult challenge because most dreamers can't control what they're doing.
Very rarely, however, dreamers experience a phenomenon known as lucid dreaming, in which a sleeper is aware that he or she is dreaming and has some level of control over actions in the dream. "About half of people have had a lucid dream, Dresler says, but "very few have them on a regular basis." Certain people can learn to dream lucidly more often. The training involves techniques such as writing down dreams and committing to remember that you're dreaming when you see a certain theme, such as a flying cow, says neuroscientist Daniel Erlacher of the University of Bern, who was not involved in the current research.
Dresler and Czisch recruited six people who had been trained in lucid dreaming, instructed them to dream that they were clenching either their left or their right hand, and then let them fall asleep in a brain scanner. Once the sleepers were dreaming and lucid, they let the researchers know by moving their eyes from left to right twice. The researchers checked the volunteers' brain activity patterns to make sure they really were in the dream phase of sleep known as rapid eye movement. The team then recorded brain activity using either functional magnetic resonance imaging (fMRI), which shows high-resolution images of brain activity throughout the brain, or near-infrared spectroscopy (NIRS), which shows activity on the surface of the brain.
Only two of the subjects were able to have lucid dreams in the noisy scanners. But in each of them, one in fMRI and one in NIRS, the researchers saw the area of the motor cortex that controls the left hand light up in the same way as in someone who was awake. The subjects were able to perform the task in two different dreams each, the researchers report online today in Current Biology. That suggests that "dreams are not just represented as a visual scene" like watching a movie, Dresler says, but involve the whole body.
"It's a clever use of that patient population," says neurologist Allen Braun of the National Institute on Deafness and Other Communication Disorders in Bethesda, Maryland. He says it's interesting that although the motor cortex, which controls movement itself, was active, the midline area of the brain, which is known to be activated when people are making a decision whether to move a limb, was not active in the lucid dreamer whose brain was imaged with fMRI. "They must know they're not really moving," he says. Although the researchers imaged only two subjects, Braun says that they have done "more than enough" to show that these two brain-imaging techniques can read lucid dreamers' dreams.
"It's a very impressive work," Erlacher says, particularly given the difficulty of getting someone to dream lucidly in a noisy scanner. To strengthen their findings, the authors plan to recruit more lucid dreamers to determine whether the brain responds similarly in everyone. And they hope to find out what happens when their dreamers perform more complex tasks such as walking, speaking, or even flying, which would help researchers interpret dreams and understand how and why the mind creates them.