(CNN)People can say all sorts of strange things in their sleep, but a new study suggests that someone in the middle of a vivid dream can understand questions -- and even answer them.
Dreams have been widely studied, and experts are still trying to understand why we have them, how dream scenarios are created, and whether dreaming benefits brain function.
But remembered dreams are often full of forgotten details and distortions, so experts from Northwestern University wanted to speak to people as they dreamt in real time, to learn more about why dreams happen, and how they might be useful for mental function.
Scientists attempted to speak to people during lucid dreams. While lucid dreaming, people report that they are aware that they are dreaming, and often say they are able to direct or manipulate the dream's content to some degree.
In separate experiments in the US, France, Germany and the Netherlands, scientists studied 36 people with varied experiences of lucid dreaming, establishing two-way communication between subjects and asking questions using sensory stimulation, including touching, beeping noises and flashing lights.
"We presented questions to individuals in the midst of lucid dreams, and they were able to answer with eye movements or muscle contractions," Karen Konkoly, cognitive neuroscientist at Northwestern and one of the paper's authors, told CNN over email.
Researchers found the dreamers could follow instructions to do simple mathematical equations, answer "yes-no" questions, and differentiate between visual tactile and auditory sensory stimuli.
"This demonstrates it is possible to correctly perceive external stimuli and perform the operations necessary for answering, all while remaining asleep," Konkoly added.
Teams found evidence of two-way communications between researchers and patients belonging to all participant categories, which included experienced lucid dreamers, healthy people trained to lucid dream with minimal experience and patients with narcolepsy.
"Our paper showed specific results from several examples from among the 29 different times when we received a correct answer to a question from a dreamer," Ken Paller, director of Northwestern's Cognitive Neuroscience Program, told CNN, adding that there were also many instances where attempts at communication were not successful. Of 158 attempts at two-way communication during REM sleep, 18.4% produced correct responses, Paller told CNN.
REM, which stands for rapid eye movement, is the stage of sleep in which we dream and information and experiences are consolidated and stored in memory.
"We only needed findings from a handful of people to convincingly demonstrate that two-way communication is possible, which was our primary conclusion. We showed that it can even happen in individuals with minimal prior experience with lucid dreaming," he said in an email.
"Our results showed that dreamers could comprehend questions correctly, hold information in working memory and manipulate information (as in math computations), and express their answers coherently.
"We have thus gained knowledge about the cognitive abilities that can be engaged during a dream. In this way, further research along these lines will hopefully reveal more about dreaming conscious experiences and how they may differ from waking conscious experiences," he said.
Researchers say that their methods could be used for further research on memory, nightmare therapy, spiritual development and problem solving.
The research was published Thursday in the journal Current Biology.