Learning by listening to things while you sleep might be a desperate last resort for budding linguists and university students cramming for their finals, but how much can the human brain actually take on board while in a state of unconsciousness?
It is fairly well-established that the brain processes information while we sleep (such as dealing with memories and ‘information of the day’) and can even respond to certain external stimuli (for instance the hypnic jerk is believed by some to be an ancient response evolved by humans to prevent us from falling from trees as we slept).
Now a team of scientists from France and the UK have tried to see whether or not our sleeping brains can process words to the point where they can understand simple meanings of those words.
So, what’s the point?
The human brain is capable of incredible things – the source of music, logic, poorly-written science blogs and language.
In order for language to work our brains need to be able to interpret the meanings of words. While this might seem like an obvious and simple task, you have to remember that individual words come loaded with various connotations and nuances (the word ‘set’ for instance is described on dictionary.com as having 100 separate meanings involving subjects as diverse as surgery, tennis and chickens).
Another level of complexity in meaning is the categorisation of a word:a simple noun such as ‘ball’ could be considered as a ‘toy’, ‘sporting equipment’ or a synonym of ‘sphere’ and can itself be sub-categorised into different types of ball.
In this study, the researchers wanted to see whether the sleeping brain can distinguish between words which are the names of animals and those which aren’t: a simple interpretation of the meaning of those words.
This kind of study could help to shed light on how our brains work and how we process information, as well as helping us to gain a better understanding of sleep – a state in which we spend around one-third of our lives (although it’s probably closer to half for teenagers and blog-writers).
What did they do?
Volunteers were placed in a dark room, each sitting back in reclining chair with their eyes closed and encouraged to drift off to sleep. Each wore an EEG (electroencephalography) cap to monitor brain activity.
While they were drifting off, the participants were played the names of objects, some of which were animals, and instructed to press a button by their left hand if they heard the name of an animal or to press on by their right hand if it was a non-animal.
Movements of the right-hand side of the body are controlled by the left hemisphere of the brain, and vice-versa, meaning that while conscious, the participants’ brains would associate animal-words with activity in the right hemisphere of their brains with non-animals with the left hemisphere.
Words were played at 6 to 9 second intervals and the participants continued to press the buttons as they descended into sweet slumber, and the words continued to be played while they slept. The EEG caps could monitor brain activity to figure out precisely when they fell asleep, but also to see if the right or left hemispheres continued to light up in response to animal or non-animal words, respectively, even though the participants were no longer pressing the buttons.
Did they prove anything?
Weirdly enough, the volunteers’ brains continued to show stimulation in their right hemispheres in response to animal words and the left hemispheres for non-animals. The scientists reckoned that this shows that their brains could still process the words and interpret the meaning of ‘animal’ and ‘non-animal’ even though the participants were asleep.
In a second experiment, volunteers were presented with a list of words, some of which they had been played while awake and unconscious, and some of which had not been played at all. They had to indicate whether or not they thought each word had been played to them.
Generally speaking, ‘participants could distinguish new words presented during wake period… but crucially not from words presented during sleep’. In other words, while the brain is able to linguistically process words during sleep to some extent, the volunteers did not remember them.
So, what does it mean?
This appears to be pretty strong evidence to suggest that the brain can process the meanings of word that we hear during sleep, at least at a fairly simplistic level of understanding, and begs the question: ‘what else can the brain do during sleep?’
It would be incredibly interesting to find out precisely how sophisticated the brain’s functions are, not only during light sleep, but at deeper stages and the highly-active REM stage too.
While the student dream of being able to learn important exam facts while sleeping off an evening of tequila and aftershocks might not have been realised, this study does provide an exciting insight into what our unconscious mind is capable of.
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Kouider, S., Andrillon, T., Barbosa, L., Goupil, L., & Bekinschtein, T. (2014). Inducing Task-Relevant Responses to Speech in the Sleeping Brain Current Biology, 24 (18), 2208-2214 DOI: 10.1016/j.cub.2014.08.016