Brain research Why we learn much more than we think while we sleep
Who hasn’t fallen asleep in front of the TV in the evening and woken up again a few hours later to find out how frightening the program can be during the night?? "Never mind!", you will say. "During sleep, you don’t hear what’s on TV."
This is also true – when it comes to conscious experience. But while we sleep, the brain is by no means lying idle. It rather uses sleep to sort out the day’s information. Thus, in problem-solving tasks, the people who not only think about a task, but are also allowed to sleep on it, perform better.
Problems are best solved at night in bed
Surprisingly, the brain can do even more, because even in sleep it is still actively listening – and this can even be measured. To do this, test subjects were first trained to react differently to words they heard: For example, when they heard the name of an animal (as in the word "horse"), they pressed a button with their left hand. When they saw an object (e.g. a book), they pressed right.
Hearing a word, classifying it, and then pressing it is something we quickly automate. So fast that they make you fall asleep. And this was quite desirable, because the test persons were in a darkened room for the experiment. While subjects slept, their brain activity could be tracked by EEG.
Interestingly, the brain continued to classify words in dreamless sleep phases: If the sleeping subjects were given animal names on their ears, the brain showed activity as if it wanted to move the left hand, simulating learning in the waking state.
Unfortunately, after waking up, the subjects did not remember the words they had heard and categorized during sleep. So learning by listening while you sleep doesn’t come easily. But even without consciousness, the brain can still actively respond to new information – and therefore it processes especially well the information we heard or looked at immediately before going to bed.
Sleep research These five simple tricks help you fall asleep
Even in sleep we listen
A tip, therefore, to all learners: If you don’t want to forget something, look at it again briefly right before you go to sleep – and then immediately turn off the light. Such a spiritual bedtime prayer has an effect during sleep, because the brain thinks, even if we think that we do not think anything.
This may be one reason why we can react precisely to stimuli during the night. When we "learn" the sound of the alarm clock it wakes us up more easily than a comparably loud but inconsequential noise. Parents of newborn babies even react particularly sensitively and wake up at the slightest sounds of the baby.
So remember: Even in our sleep we listen. And even if you don’t remember the TV program – who knows what traces it leaves in your brain?