“To sleep, perchance to dream”—Shakespeare may not exactly have been talking about our nocturnal journeys to another world, but that does not make the phenomenon of dreams any less mysterious or meaningful. Recent research is expanding our understanding—and yielding insights into consciousness itself.

Sleep provides science with a way to study consciousness in all its various forms, from vivid dreams to no awareness at all, says neuroscientist Benjamin Baird. When subjects are snoozing, researchers can isolate conscious experiences from the confounding influence of the senses.

In a recent attempt to peek inside the dreaming brain, Baird and leading consciousness expert Giulio Tononi, both at the University of Wisconsin–Madison, and their colleagues used scalp electrodes to record sleepers’ brain waves via high-density electroencephalography. They woke people at frequent intervals to ask if they had been dreaming and, if so, what their dreams were about. One of their experiments garnered a total of about 200 such waking accounts from 32 subjects, and a second added some 800 more from a smaller group specially trained in dream reporting.

The team identified a “hot zone” in a posterior cortical region, near the back of the head, where low-frequency brain waves (linked to unconsciousness) decreased and high-frequency activity rose when people said they had been dreaming—regardless of whether or not it was during rapid eye movement (REM) sleep. (Despite common belief, dreaming can occur during both REM and non-REM sleep.) The findings were described in Nature Neuroscience.

In a third experiment with seven subjects, the scientists predicted with 87 percent accuracy whether participants were dreaming. Furthermore, brain-wave activity in certain brain regions was linked to specific dream content—including locations, faces and speech. These same areas are activated during waking experience. “We didn’t actually try to predict [dream] content in this study,” Baird notes, but he says that would be an exciting “potential direction.”

This approach represents “a really cool and innovative paradigm,” says neuroscientist Christof Koch of the Allen Institute for Brain Science in Seattle, who was not involved in the work and who serves on Scientific American’s board of advisers. Finding that dream-related activity was focused toward the back of the brain was surprising, he says, because consciousness is widely thought to arise in frontoparietal regions. One limitation of the study is the delay between a subject waking up and recounting a dream. Ultimately, Koch says, “we want to get closer and closer to the experience itself.”