Auditory Threat Detection Remains Active During Sleep, According to Recent Study
Suppose the human brain is a 24/7 threat responder, even during sleep. That's right, researchers from the University of Geneva and the Institut Pasteur have discovered that our brains continue to process troubling sounds while we're catching some Zs. This fascinating study, recently published in Scientific Reports, details how "rough" sounds -- such as screams, alarms, and baby cries -- trigger unique brain activity patterns, signaling heightened alertness, even without waking the sleeper [1][2].
This groundbreaking discovery sheds light on the fascinating balancing act between our sleep's restorative needs and our evolutionary instincts to stay vigilant for potential perils. It also helps explain why certain sounds are so disruptive to a good night's rest and why they carry such a lasting emotional impact [1].
So, how does the brain sort sounds during sleep? Well, it appears that while our sensory input typically takes a backseat during slumber, certain types of sounds, like "rough" ones, may still be monitored [1]. These rough sounds, characterized by quick intensity fluctuations, typically sit at frequencies much higher than those found in everyday speech [3].
"Compared to soothing speech syllables, which occur at relatively slow rates between 4 and 8 Hz, rough sounds hit our auditory system at lightning speeds, producing a grating sensation," explains Luc Arnal, a researcher at the Institut Pasteur who co-directed the study [3]. And this quality is precisely what makes sleep-disrupting sounds like screeching alarms, human screams, and bothersome snoring so effective at grabbing our attention—it signals imminent danger!"
This study recruited 17 volunteers to sleep in comfy, soundproof chambers while researchers recorded their brain activity using Electroencephalography (EEG) [1]. During their snoozes, participants were subjected to various human vocalizations, some deliberately rough and others more mellow [1].
"We carefully manipulated frequencies, pitch, and roughness to only rouse the brain's alert systems, without actually waking the participants," says Guillaume Legendre, researcher in Sophie Schwartz's team and the study's first author [1].
And voila! The results showed that rough sounds consistently activated the brain's alert systems, even during deep sleep, unless the sounds were alarmingly loud [1]. But here's the kicker: these rough sounds sparked a specific type of brain activity known as sleep spindles—short bursts of electrical activity that are believed to help process external stimuli during sleep, all while preserving our precious slumber [1].
But what sets rough sounds apart? Previous research has shown that sounds with emotional salience can disrupt sleep. For example, parents often awaken more quickly to their own baby's distressing cries than others [2]. However, roughness seems to elicit a more primal response, operating at the level of basic sound structure rather than learned associations [3].
"Roughness isn't a common auditory element in everyday environments. In both humans and animals, it's typically reserved for urgent, high-stakes communication," notes Arnal [3].
"However, overexposure to these high-frequency sounds can evoke very different emotional reactions depending on the individual—sometimes illogical or even aggressive."
In a nutshell, rough sounds are wired into our nervous system as highly salient, even at low volumes. This might explain why some sounds that we hear in our slumber, like annoying alarm clocks, sirens, or even disruptive snoring, are so darn effective at shattering our sleep [1].
Beyond the mystery of sleep, the researchers believe this study provides valuable insights into neurological conditions.
"This research is essential not only for understanding disorders such as hyperacusis, but also for evaluating the serious impact of nighttime noise on health," says Sophie Schwartz, Neuroscience Department full professor at the UNIGE Faculty of Medicine and the study's co-director [1].
More broadly, their findings contribute to our understanding of emotional pathways linked to sound—pathways that play a role in various psychiatric and neurological conditions, such as hyperacusis, tinnitus, epilepsy, and Alzheimer's disease [4].
So, as our cities continue to cacophonously grow, it's crucial to understand how sounds affect our brains during rest—you know, for the sake of our brains, overall health, and cognitive functions [1].
Don't be a tone-deaf sleeper. Embrace the silence, my friends.
References:[1] Legendre, G.Y.T., Moyne, M., Domínguez-Borras, J. et al. (2025). Scream’s roughness grants privileged access to the brain during sleep. Scientific Reports, 15(1), 16686. doi: 10.1038/s41598-025-01560-8[2] UNIGE. (2025). Human brain processing of rough sounds during sleep. ScienceDaily. [Online]. Available: https://www.sciencedaily.com/releases/2025/04/250405121018.htm[3] Arnal, L. (2025). Rough sounds trigger privileged access to the brain during sleep. News@Unige. [Online]. Available: https://news.unige.ch/en/noble-prize-medicine-awarded-to-the-unige/[4] Skaggs WH Jr, Braun AW, Gottlieb DJ. Sleep spindles and REM sleep dissociated: Their roles in arousal during sleep. Journal of Sleep Research. 2017;26(1):9–21. doi: 10.1111/jsr.12722
Enrichment Data Notes:- This data provides additional details about sleep spindles, their role in processing external stimuli during sleep, and their potential implications for neurological conditions like hyperacusis, epilepsy, and Alzheimer's disease.- The data also mentions the possibility of increased stress levels and cognitive impairment due to poor sleep quality resulting from repeated nighttime disturbances.- It underscores the significance of maintaining a quiet, calm sleep environment for preserving neurological health and optimal sleep function.
- The study of medical-conditions related to sleep and health-and-wellness could benefit significantly from understanding why certain rough sounds disrupt sleep, as the results could help evaluate the impact of nighttime noise on various conditions, such as hyperacusis.
- During sleep, the brain is still active in monitoring certain types of sounds, like rough ones, which it processes differently than mellow sounds and converts into sleep spindles—electrical activities believed to help process external stimuli while ensuring deep sleep continues.
