Sleeping Brain Capable of Understanding Words

For the first time, a team at the Laboratoire de Sciences Cognitives et Psycholinguistique in Paris appear to have demonstrated that the brain can categorise words, despite being asleep.

The idea of being able to utilise the time we spend asleep, such as through being able to learn a new language, has tantalised researchers since the dawn of psychology. Unfortunately, since a seminal study by Simon and Emmons (1956), the field has largely dismissed the idea that the brain can meaningfully process external stimuli whilst in a state of sleep.

However, a recent study by Koudier and colleagues (2014) provides an interesting rebuttal to this long held belief. Participants’ in this study were given a simple auditory word categorisation task whereby they were required to either press a button with their left or their right hand depending on whether they were played a word that was either related to an object or to an animal. The twist was that subtle cues, such as dim lighting, were provided in order to prompt the participants’ to fall asleep during the experiment. Additionally, participants’ were fitted with an EEG cap to record their brain activity throughout the experiment and therefore, it was possible to monitor how their brain’s responded to the ongoing word categorisation task, should participants’ succumb to a sleep state.

Obviously it is not possible for the participants’ to physically press the appropriate button while asleep. So, in order to circumnavigate this problem the researchers used the EEG recording to determine which activity patterns were occurring while the task is consciously performed and compare that with the activity patterns which occur when participants drift off to sleep. Remarkably, the activity patterns recorded during a sleep state were very similar to those recorded when the participants were consciously performing the word categorisation task. This suggests that, despite being in a sleep state, the brain appeared to be capable of categorising auditory words as either an animal or an object.

This is the first study using a relatively robust design to demonstrate that the brain may be able to perform high-level cognitive tasks while in a sleep state. That is not to say the design was perfect, for example, it was not possible to be certain that participants’ were truly asleep during the experiment. Furthermore, the depth of this cognitive processing is questionable. Without having a conscious experience (as far as we know) does the sleeping brain have a true understanding of the words that it is supposedly categorising? Or is it simply responding ‘automatically’, in a similar way to a dog sitting upon command without a true understanding for human language or the concept of sitting itself (again, as far as we know)? Nonetheless, this study provides a fascinating insight into the cognitive capacities of our brain during a state of sleep and will perhaps rejuvenate studies of this nature to elaborate its findings.



Kouider S, Andrillon T, Barbosa LS, Goupil L, & Bekinschtein TA (2014). Inducing task-relevant responses to speech in the sleeping brain. Current Biology, 24 (18), 2208-14 PMID

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