Researchers say two-way communication is possible with people who are asleep and dreaming.
Specifically, with people who are lucid dreaming — that is, dreaming while being aware you're dreaming.
In separate experiments, scientists in the U.S., France, Germany and the Netherlands asked people simple questions while they slept. Sleepers would respond by moving their eyes or twitching their faces in a certain way to indicate their answers.
"Since the '80s, we've known that lucid dreamers can communicate out of dreams by using these signals," says Karen Konkoly, a Ph.D. student at Northwestern University who is the first author on the study published this month in Current Biology.
"But we were wondering, can we also communicate in? Can we ask people questions that they could actually hear in their dreams that we could kind of have a more meaningful conversation?"