When I can't sleep, I think about what I'm missing. I glance over at my wife and watch her eyelids flutter. I listen to the steady rhythm of her breath. I wonder if she's dreaming and, if so, what story she's telling to herself to pass the time. (The mind is like a shark — it can't ever stop swimming in thought.) And then my eyes return to the ceiling and I wonder what I would be dreaming about, if only I could fall asleep.
Why do we dream? As a chronic insomniac, I like to pretend that our dreams are meaningless narratives, a series of bad B-movies invented by the mind. I find solace in the theory that all those inexplicable plot twists are just random noise from the brain stem, an arbitrary montage of images and characters and anxieties. This suggests that I'm not missing anything when I lie awake at night — there are no insights to be wrung from our R.E.M. reveries.
Unfortunately for me, there's increasing evidence that our dreams are not neural babble, but are instead layered with significance and substance. The narratives that seem so incomprehensible — why was I running through the airport in my underwear? — are actually careful distillations of experience, a regurgitation of all the new ideas and insights we encounter during the day.
Look, for instance, at the research of Matthew Wilson, a neuroscientist at the Picower Institute at M.I.T. In the early 1990's, Wilson was recording neuron activity in the brains of rats as they navigated a difficult maze. (The machines translated the firing of brain cells into loud, staccato pops.) One day, he left the rats connected to the recording equipment after they completed the task. (Wilson was preoccupied with some data analysis.) Not surprisingly, the tired animals soon started to doze off, slipping into a well-deserved nap. And that's when Wilson heard something extremely unexpected: although the rats were sound asleep, the sound produced by their brain activity was almost exactly the same as it was when they were running in the maze. The animals were dreaming of what they'd just done.