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Eyes really do watch dreams
Mouse eye cells
Scientists suspected for a long time that dreamers look at things with their physical eyes while they sleep, but they couldn't prove it. In one study, researchers examined the eye directional cells in mouse brains and found them in sync with where the mouse's eyes were looking at any point during REM sleep.
Lucid dreamers trace a circle
A second study used lucid dreamers, people who know they are dreaming. They were asked to imagine a circle in the dream, and then to trace a circle with a thumb and look at it. Imagining the circle made their eyes move in a stuttery, stepwise path, the same path an awake person's eyes take when picturing a shape. Watching the dream thumb made their eyes move smoothly, the way they do in waking life when we look at a real object.
The paralyzed body
REM sleep also paralyzes the body, which is thought to keep people from acting out dreams they experience as reality.
Why do researchers study lucid dreamers?
Lucid dreamers can signal from inside a dream, which gives scientists a way to time what happens in it. In the early 1980s, Stephen LaBerge at Stanford University showed that dreamers could make agreed left-right eye movements during REM sleep, and the recordings matched the signals. Because the rest of the body is paralyzed, the eyes become a channel from the dream to the lab. The technique lets researchers mark the moment a dreamer begins a task and compare it with the eye recording.
What keeps the body still during REM?
Neurons in the brainstem send signals during REM that block the motor neurons in the spinal cord, so most voluntary muscles go limp. The muscles that move the eyes and the diaphragm are spared, which is why the eyes can dart and breathing continues. In the 1960s, French researcher Michel Jouvet found that cats with damage to a small area of the brainstem rose and seemed to act out dreams during REM. The finding showed that the paralysis is switched on by a specific brain circuit.
Why did the dream thumb make eyes glide?
Eyes move in two main ways. They jump in quick jerks called saccades when scanning a scene or picturing a shape, and they glide in smooth pursuit when following a moving object. Most people cannot produce smooth pursuit without something moving to follow. A person imagining a circle with nothing in view gets the jumpy path instead.
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