Sleeping with your eyes wide open
ETHZ researchers kept an open eye on what was happening during sleep – apparently a lot more than we assumed
From the report:
Our eyes are typically closed when we sleep. However, there is a flurry of activity taking place beneath our closed eyelids: a team of researchers, led by principal investigators Caroline Lustenberger, Sarah Meissner and Nicole Wenderoth from the Neural Control of Movement Lab at ETH Zurich, have observed that the size of the pupil fluctuates constantly during sleep. Sometimes it increases in size, sometimes it decreases; sometimes these changes occur within seconds, other times over the course of several minutes.
“These dynamics reflect the state of arousal, or the level of brain activation in regions that are responsible for sleep-wake regulation,” says Lustenberger. “These observations contradict the previous assumption that, essentially, the level of arousal during sleep is low.”
Instead, these fluctuations in pupil size show that even during sleep, the brain is constantly switching between a higher and lower level of activation. These new findings also confirm for humans what other research groups have recently discovered in studies on rodents, who also exhibit slow fluctuations in the activation level (known in the field as arousal). The study by the ETH researchers was recently published in the journal Nature Communications.
New method for an old mystery
The regions of the brain which control the activation level are situated deep within the brainstem, making it previously difficult to directly measure these processes in humans during sleep. Existing methods are technically demanding and have not yet been established in this context. The ETH researchers’ study therefore relies on pupil measurements. Pupils are known to indicate the activation level when a person is awake. They can therefore be used as markers for the activity in regions situated deeper within the brain.
The ETH researchers developed a new method for examining the changes in people’s pupils while asleep: using a special adhesive technique and a transparent plaster, they were able to keep the eyes of the test subjects open for several hours.
“Our main concern was that the test subjects would be unable to sleep with their eyes open. But in a dark room, most people forget that their eyes are still open and they are able to sleep,” explains the study’s lead author, Manuel Carro Domínguez, who developed the technique.
Analysis of the data showed that pupil dynamics is related not just to the different stages of sleep, but also to specific patterns of brain activity, such as sleep spindles and pronounced deep sleep waves – brain waves that are important for memory consolidation and sleep stability. The researchers also discovered that the brain reacts to sounds with varying degrees of intensity, depending on the level of activation, which is reflected in the size of the pupil.
If you enjoyed this article, you will like the following ones: don't miss them by subscribing to :
