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The brain can make decisions while you sleep

A doctoral student, Thomas Endrilon and a senior research associate, Sid Kudier, in their article for The Conversation magazine, described the research they conducted and proved that the brain also makes decisions during sleep.

The idea of ​​separating our mind from the outside world during sleep is very old and still deeply ingrained in our understanding of sleep today, despite everyday experiences and recent scientific discoveries that tend to prove that our brains are not completely excluded from their environment.

On the contrary, our brains may leave little room for the outside world. For example, we wake up easier when we hear our own name or a specifically loud sound such as an alarm or fire alarm compared to equally loud but less important sounds.

In a study published in the journal Current Biology, we went a step further to show that complex stimuli are not only processed while we sleep, but that this information can be used to make decisions just as much as when we are awake.


Our approach was simple: we based it on knowledge of how quickly the brain processes complex tasks. Driving a car, for example, requires gathering a lot of information at the same time, making quick decisions and guiding them through complex motor actions. You can drive all the way home without remembering anything, which is what we do when we say we are on autopilot.

When we sleep, the brain regions crucial for paying attention or carrying out instructions are of course shut down, which makes starting a task impossible. However, we wanted to see if any processes continued in the brain after sleep was completed if task participants were previously given an automated task.

To do this, we performed experiments in which we asked participants to categorize spoken words that were divided into two categories: words referring to animals or objects, for example: cat, hat in the first experiment; then they make words like: hammer versus pseudo words (those that are pronounced but can’t be found anywhere in the dictionary) like fabu.

Participants were asked to place the word they heard in a certain category by pressing the left or right button. When the task became more automated, we asked them to continue, but they were allowed to fall asleep. As they lay in a dark room, most of them fell asleep while the words were released.

At the same time, we monitored their alertness thanks to EEG electrodes placed on their heads. As soon as they fell asleep and without interrupting the flow of words they were listening to, we gave the participants new items from the same categories. The aim was to force them to extract the meaning of the word (in the first experiment) or to check whether the word was part of a token (in the second experiment) in order to be able to answer.

Of course, when they fell asleep, the participants stopped pressing the button. To check if their brains continued to respond to words, we observed activity in the motor areas of the brain. When you plan to press the left button it engages your right hemisphere and vice versa. By observing the truth of brain activity in the motor areas, it is possible to see if someone is preparing an answer and to which side. By applying this method to our sleepers, we proved that even during sleep, their brains continued to routinely prepare for left or right answers according to the meaning of the words they listened to.

What is even more interesting, at the end of the experiment and after they woke up, the participants did not remember the words they heard during sleep, although they remembered very well the words they heard while they were awake. Not only did they process complex information while they were completely asleep, but they did so unconsciously. Our job is to develop the brain’s ability to process information not only during sleep, but also during the unconscious state.

This research is just the beginning. Important questions have yet to be answered. If we can prepare for sleep activities, why not do them? What kind of processing can or cannot be achieved when the brain is asleep? Can one or groups of sentences be processed? What happens when we dream? Would these sounds be combined into a dream scenario?

Most important of all, our work revives the ancient fantasy of learning during sleep. It is well known that sleep is important for consolidating previously learned information or that some basic form of learning such as exercise can occur while we sleep. Yet, can more complex forms of learning happen and what would be the cost of brain sacrifice to make this happen?

Sleep is important for the brain and complete sleep deprivation leads to death after about two to four weeks. It should be borne in mind that sleep is an essential phenomenon and universal for all animals. This proves that it is not true that during sleep the stimulus is answered completely or not at all, but not that forcing our brains to learn and do things at night would be useful in the long run.

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