Adventures in Sleep-Listening

Adventures in Sleep-Listening

By Adanya Lustig, Linguistics 2018

New insights into consciousness pioneered by Dr. Sid Kouider and colleagues at École Normale Supérieure, a research institution in Paris, have shown just how much we can do while asleep.

In the first experiment, participants sat in a chair and listened as words were read to them. As the subjects heard the words, they pushed a button in their right or left hand depending on whether the word was an animal or an object. Simple enough, right? But how well would they be able to complete the task after falling asleep? While the subjects fell asleep the researchers continued reading the words, and they measured the Lateralized Readiness Potential of the subjects. The Lateralized Readiness Potential (LRP) is an electrophysiological tool to measure someone’s response to a stimulus and subsequent reaction.

While awake, when you respond to something with your left hand, the LRP is noticeable at the scalp over the motor/premotor cortex of the right side of your brain (and vice versa) in two peaks. One peak is a significant early deflection that occurs while the brain is preparing a response plan and the other peak is an opposite and later deflection that appears to occur after a manual response. Once asleep, the subjects were not pushing any buttons, but that first peak in LRP was still present, suggesting that the brain was still preparing to respond with the correct hand.

The big question here, however, is how do the researchers know when anyone is asleep? What stage of sleep is asleep enough? The researchers found that the participants showed this change in LRP during both non-rapid eye movement 1 (NREM1) sleep and non-rapid eye movement 2 (NREM2) sleep. In order to assure that the participants were in fact asleep, they looked at a number of measures like unresponsiveness and electrophysiological occurrences. Additionally, they had neurophysiologists blind to the study tracking the patients for these signs of awareness. They still feared, however, that the results taken during NREM1 sleep, the earlier stage, were not good enough. So, they designed a second experiment.

This experiment had a similar premise — word processing while asleep, but they changed a few key variables. First, the choice subjects had to make was no longer animal or object,but word or non-word. These non-words or pseudowords are meaningless but they sound like real words. For example, something like “runk” could be a pseudoword, but “igbladoobob” probably wouldn’t make the list because it sounds a little silly.

The other changes were all an attempt to verify that the subjects were asleep: the researchers only counted the results of subjects in NREM2 and they changed the methods. Instead of the subjects falling asleep in the middle of the study, they had them start the experiment while awake, paused, let them fall asleep, and gave them the second set of stimuli only after the appearance of a K complex or sleep spindle was noted, which signifies NREM2 sleep. In order to verify again that the participants were truly asleep, they gave them a posttest with the set of words from when they were awake, the words presented while asleep, and random new words. The participants could only remember the words that were presented while awake.

Even with all these changes, subjects from both studies showed the same electrophysiological signs, implying that humans can perform semantic differentiation and classification of lexical properties and prepare to respond while asleep. This means that with a little practice (the part of the study completed while awake) the participants could go around the prefrontal region and make these classifications automatically, and even reach higher processing levels up to preparing to move the hand. The implications of this are huge, in terms of concepts like learning or working while asleep.

The researchers asked several further questions, such as where in the neural stream between preparing a motor response and executing that motor response the stop-up occurred. It also remains to be seen if the same kind of processing could occur in later stages of sleep where the cortex is not so active. This study raises many further questions on the topic of consciousness, and how much we can do while unconscious.