(Thomas Andrillon) The idea that during sleep our minds shut down from the outside world is ancient and one that is still deeply anchored in our view of sleep today, despite some everyday life experiences and recent scientific discoveries that would tend to prove that our brains don’t completely switch off from our environment.
On the contrary, our brains can keep the gate slightly open. For example, we wake up more easily when we hear our own name or a particularly salient sound such as an alarm clock or a fire alarm compared to equally loud but less relevant sounds.
In research published in Current Biology, we went one step further to show that complex stimuli can not only be processed while we sleep but that this information can be used to make decisions, similarly as when we’re awake.
Our approach was simple: We built on knowledge about how the brain quickly automates complex chores. Driving a car, for example, requires integrating a lot of information at the same time, making rapid decisions and putting them into action through complex motor sequences. And you can drive all the way home without remembering anything, as we do when we say we’re on “automatic pilot.”
When we’re asleep, the brain regions critical for paying attention to or implementing instructions are deactivated, of course, which makes it impossible to start performing a task. But we wanted to see whether any processes continued in the brain after sleep onset if participants in an experiment were given an automatized task just before.
To do this, we carried out experiments in which we got participants to categorize spoken words that were separated into two categories: words that referred to animals or objects — for example “cat” or “hat,” in a first experiment; then real words like “hammer” vs. pseudo-words (words that can be pronounced but are found nowhere in the dictionary) like “fabu” in a second one.
Participants were asked to indicate the category of the word that they heard by pressing a left or right button. Once the task became more automatic, we asked them to continue to respond to the words, but they were also allowed to fall asleep. Since they were lying down in a dark room, most of them fell asleep while words were being played.
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