We process our world differently when we’re stressed out, and so, too, do mice. According to a new paper in PLOS Biology, mice perceive sounds in a different way when they’ve been subjected to repeated stressors, responding to some louder sounds as if they were softer.
“We found that repetitive stress alters sound processing,” the study authors stated in their paper. “These alterations in auditory processing culminated in perceptual shifts, particularly a reduction in loudness perception.”
Read More: How Do Other Animals See the World?
Brain Processing Under Chronic Stress
Though an abundance of research has recognized that chronic stress impacts our complex cognition, impairing processes like learning and memory, far fewer studies have looked into the impacts of chronic stress on our senses.
“There remains a notable gap,” the study authors stated, “in our understanding of its influence on fundamental cortical functions, such as sensory processing.”
In fact, of the few studies that have tested how chronic stress shapes the perception of stimuli, most have tested how chronic stress shapes the perception of negative stimuli — things as terrible as pain and unpleasant smells.
“There is little research on how our brains process neutral sounds under chronic stress,” said study author Jennifer Resnik, an assistant professor at Ben-Gurion University of the Negev in Israel, in a press release.
To tease out the impacts of stress on neutral sensory processing, the study authors turned to mice. Confining the mice to a small space for thirty minutes a day over the course of a week and then assessing their responses to sound with a behavioral task, the team revealed that the mice’s perception of loudness was reduced, as seen by their tendency to treat some louder sounds as softer sounds.
“Our research suggests that repeated stress doesn’t just impact complex tasks like learning and memory,” Resnik said in the release. “It may also alter how we respond to everyday neutral stimuli.”
Read More: What Animals Can Sense That Humans Can’t
Quiet for a Mouse
It isn’t a simple task to figure out how loud a sound seems to a mouse. To arrive at their results, the study authors trained mice to identify three types of sounds — low-intensity (at 40 to 45 dB), mid-intensity (at 50 to 70 dB), and high-intensity (at 75 to 80 dB) — as “soft” or “loud” by licking one of two water spouts, a “loud spout” and a “soft spout,” in the lab.
If the mice correctly identified a low-intensity sound as soft by licking the soft spout or a high-intensity sound as loud by licking the loud spout, they were rewarded with a taste of sweetened water. They were also rewarded with a taste whether they identified a mid-intensity sound as soft or loud.
Testing the mice before their week of stress and after, the study authors found that the animals’ tendency to identify low-intensity sounds as soft and high-intensity sounds as loud remained the same, though their labelling of mid-intensity sounds changed. Impaired by stress, they were more likely to report mid-intensity sounds as soft than loud, indicating their reduced perception of loudness.
While the stress didn’t alter what the mice were able to hear, as seen in the activity in their auditory brainstems, it did alter their perception of what they heard. Indeed, brain images of the mice showed that their altered perception correlates to increased activity in some sensory cells and decreased activity in others — a unique combination that could connect to the overall softening of their sound perception.
Additional research could catch similar sound perception changes in other chronically stressed animals. Until then, another press release states that the results reveal that a stressed-out mouse is a less sensitive one, at least in terms of neutral sounds.
“Our findings provide insight into a possible mechanism by which repetitive stress alters sensory processing and behavior,” the study authors concluded in their paper, “challenging the idea that stress primarily modulates emotionally charged stimuli.”
Read More: What Are the Loudest Animals in the World?
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
Sam Walters is a journalist covering archaeology, paleontology, ecology, and evolution for Discover, along with an assortment of other topics. Before joining the Discover team as an assistant editor in 2022, Sam studied journalism at Northwestern University in Evanston, Illinois.
