Well guilty as charged! I’m indeed one of those ‘lucky’ ones that you all envy. I can sleep through almost any din and bustle and wake up fresh as a daisy the next morning. Nothing, other than sudden hunger pangs at odd hours, can disturb my otherwise seamless slumber. The only exception was the night before my Ph.D. defense when I was woken up by a panic attack, and in my three decades of existence, that was probably the only time it happened. My reputation precedes me, and I’m referred to as Kumbhakarna in my close circle.
My sister, sadly, is exactly the opposite! The rustling of bedsheets, the softest tap on the door or the gentlest of breeze are enough to wake her up. She struggles to remain asleep while I snore away to glory in that very room, blissfully unaware of the mundane world around me. But what is it that makes me so impervious to noise? Is my brain wired differently and so responds (or doesn’t) to sound in peculiar ways?
I may not be reacting to sounds around me while I sleep, but the brain is always listening. It continues to register and process sound on a basic level, even when we are sound asleep. It’s actually good, because even though we may not react to all sorts of noise, a firm alarm wakes us up with a jolt.
One of the methods to understand our brain during sleep is electroencephalogram (EEG). It records the ‘brain waves’ which are nothing but the synchronized bouts of electrical activities from masses of neurons talking to each other either to execute a task or not do anything at all. To register these activities, scientists place electrode patches on the scalp of a sleeping person and record, especially from the brain’s thalamocortical system. As we progress through the different stages of sleep, our brain produces different types of brain waves. Every rise, fall, and jitter of these waves tell us a different story about our thoughts, emotions, and behaviors.
How much noise can disturb our sleep depends on several factors like which stage of sleep we are in. That is the reason why it is more probable that noises will wake us up from light sleep, rather than from deep sleep.
Interestingly, a study led by Thanh Dang-Vu and Ellenbogen found that for “sound sleepers”, specific brain waves may make them more tolerant to noise.
They did a tad bit mean experiment on healthy volunteers in their sleep laboratory for three nights. On the first night, participants could sleep blissfully in their comfy beds. However, for the next two consecutive nights, the researchers placed a speaker behind the beds and played everyday noises, such as alarm clocks or toilets flushing, at varying volumes and noted how loud noise had to be before arousing each person. All these nights Thanh Dang-Vu and team kept recording the brain waves.
They showed that brain activity in the face of noise is controlled by specific brain waves during sleep. In particular, waves called sleep ‘spindles’ prevent the transmission of sounds to auditory brain regions. In contrast, when sounds were associated with brain waves called ‘K-complexes‘, activation of auditory areas was larger, and individuals were prone to waking up.
In another study, Thanh Dang-Vu resorted to using EEG in combination with functional magnetic resonance (fMRI) imaging on 19 healthy individuals. The idea was to not just monitor the brain waves, but also to visualize which brain areas light up in response to sound during sleep. Here, he and his colleagues found that sound, when the person is awake, activates two main brain regions thalamus and primary auditory cortex. These responses persist during deep NREM sleep, except throughout spindles, during which they became less consistent. When sounds elicited a K complex, the activity in the auditory cortex was enhanced.
So, it could be that those who are blessed with more sleep spindles and/or less K-complex, could sleep even in a loud environment. However, during sleep, our brain produces both K-complexes and sleep spindles, depending on the stage of sleep. Therefore, our perception of the environment is not continuously reduced, it rather varies throughout during sleep.
Several other factors may make our brain respond to sound in certain ways as well. Like the time of the day when we go to sleep and even how we associate with specific sound itself. That’s plausibly why a parent can sleep soundly through their partner’s snoring but wakes up immediately when their baby cries at night.
So, the next time you lie tossing and turning in bed thanks to your teenage neighbour’s blaring stereo, you know who to blame for your ordeal.
This article is edited by Rashmi Guha Ray. She is a journalist from India whose undying passion for politics carried her to the western shores to study MA in Conflict, Governance, and Development in the University of York, UK. She is currently working as a research assistant in a project on migration. A trained editor who is hopelessly in love with words, Rashmi loves taking up new challenges in editing and rewriting.
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