It turns out that our brains do way more when we snooze than was once thought -- and a new study suggests we can even identify and categorize words while we're sleeping.
"We show that the sleeping brain can be far more 'active' in sleep than one would think," study co-author Sid Kouider, a cognitive neuroscientist at the Ecole Normale Supérieure in Paris, said in a written statement. "Far from falling [into] a limbo when we fall asleep, parts of our brain can routinely process what is going on in our surroundings and apply a relevant scheme of response."
For their study, the researchers used an electroencephalogram (EEG) to record the brain activity of 18 men and women as they completed a word classification task.
The task involved listening to spoken words and then pressing a button using either the right or left hand to classify each word as being an animal (right hand) or an object (left hand).
The researchers then placed each person in a dark room to complete the word classification tasks as they nodded off, and after they had fallen asleep -- and the researchers recorded each person's brain activity again.
What did the researchers find?
Just like when they were awake, people eerily could classify the words accurately while asleep. The same brain activity that triggered the left or right hand to push buttons when a person was awake occurred when the person was asleep too, even though the hand wouldn't physically move during sleep.
The only difference was it took people two to three times longer to decide in which category a word belonged while they were sleeping.
"What we've been able to show here is that you can go all the way up to making decisions, to preparing actions," Kouider told The Christian Science Monitor.
In a written statement, he added that the study "explains some everyday life experiences such as our sensitivity to our name [being called] in our sleep, or to the specific sound of our alarm clock, compared to equally loud but less relevant sounds."
Future studies may determine whether we could take advantage of our brain's processing ability and complete automated tasks while we're asleep, but Kouider warns, "Research focusing on how to take advantage of our sleeping time must consider what is the associated cost, if any, and whether it is worth it."
The study published online in the journal Current Biology on September 11, 2014.