When people practice simple word classification tasks before falling asleep their brains will continue to go over these exercises even though they are not conscious.
A recent study suggests some parts of the brain behave similarly no matter if we are awake or asleep, Cell Press reported.
"We show that the sleeping brain can be far more 'active' in sleep than one would think," said Sid Kouider of Ecole Normale Supérieure in Paris. "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. This explains some everyday life experiences such as our sensitivity to our name in our sleep, or to the specific sound of our alarm clock, compared to equally loud but less relevant sounds."
The study tapped into earlier work that looked at subliminal processing by showing that speech processing and other complex tasks "can be done not only without being aware of what you perceive, but [also] without being aware at all," Kouider said.
The researcher believes such unconscious processing isn't restricted by how complicated the task is, but by whether or not it can be made automatic.
To make their findings researchers at the University of Cambridge recorded the EEG of human participants while they were awake. The study subjects were asked to identify spoken words and either animals or objects by pressing a button, using the right hand for animals and left for objects. This procedure allowed the team to compute lateralized response preparations by mapping each word category to a specific movement in the brain.
The participants were also tested while asleep; they drifted off as the word classification continued. Once asleep the study subjects were given an entirely new list of words, their brain activity suggested they continued to respond accurately if not more slowly.
The findings suggest any task that can be automated will most likely be continued during sleep, but tasks that can't be automated probably stop as sleep sets in.
The findings were published Sept. 11 in Current Biology.
