New research reveals that prolonged stress alters brain function, reducing sensitivity to sound over time. This study uncovers how the brain adapts to chronic stress, prioritizing other senses while dampening auditory perception. Could stress be reshaping how we hear the world?
Study: Repeated stress gradually impairs auditory processing and perception. Image Credit: PeopleImages.com - Yuri A / Shutterstock.com
In a recent study published in the journal PLOS Biology, researchers determined the mechanisms by which repetitive stress alters sound processing and reduces mice's perception of loudness.
How does stress impact cognition?
Repetitive stress is a significant contributor to psychiatric and sensory disorders. This type of stress triggers adaptive responses in both the central and peripheral nervous systems, ultimately resulting in behavioral changes to manage the altered internal state. Unlike acute stress, which triggers rapid and transient defensive responses, chronic or repetitive stress persists even after the initial sensory stimulus has been removed.
Several studies have highlighted the impact of repetitive stress on cognitive processes like learning, memory, and decision-making. However, it remains unclear how chronic stress influences basic cortical functions, such as sensory processing.
Sensory experiences are intricately associated with the body’s internal state, which can significantly influence an individual’s perception of a given stimulus. For example, the intensity of surrounding sounds or odors may appear stronger to an individual experiencing stress.
In the current study, researchers assess repetitive stress-mediated changes in auditory cortex activities and auditory-guided behaviors in mice to explore whether repetitive stress modulates sound processing and the perception of neutral sounds.
Study findings
Experimental mice were exposed to 30 minutes of restraint stress daily for seven days, following which physiological and behavioral stress markers were assessed.
Restraint stress led to a significant rise in corticosterone levels, which remained high for over one hour. As the researchers continued to expose the mice to restraint stress, corticosterone levels before restraining the mice increased, a symptom characteristic of chronic stress. No signs of habituation were observed in this experiment.
Persistent restraint stress also led to reduced activity levels during an open field test that remained consistent after seven days of undergoing restrain stress. Notably, this form of mild restraint stress did not significantly impact glucocorticoid receptor (GR) expression in the primary auditory cortex of the brain.
To determine the impact of repetitive stress on sensory processing and perception, the researchers performed chronic two-photon calcium imaging to monitor the activity of parvalbumin-expressing (PV) and putative pyramidal neurons (PPys) in awake mice. During repetitive stress, PPYs and PV neurons significantly reduced their intensity, particularly when mice were exposed to sound at a moderate intensity.
No significant change in the percentage of sound-responsive PV cells was observed. Notably, control mice not exposed to daily restraint stress exhibited no changes in noise-evoked activity.
During receptive stress, PPY neurons exhibited an increase in activity both before and after being exposed to white noise. The rise in PPY neuron activity during the post-sound period varied depending on the intensity of the noise.
Repetitive stress induces a reduction in sound-evoked cortical activity in an intensity-dependent manner.”
Previous studies have reported that chronic stress increases somatostatin expression in the dorsal hippocampus of male rats and alters the structure of somatostatin-expressing cells. In the current study, the researchers observed that similar to PPys and PV cell activity, the expression of somatostatin-expressing inhibitory (SST) cells increased during both pre- and post-sound periods. However, a greater difference between SST cell activity was observed during pre- and post-sound periods while under repetitive stress.
Chronic stress was found to reduce PPy and PV noise-evoked activity, whereas increased activity of SST cells was observed. Thus, chronic stress appears to have a cumulative effect on sound processing dependent upon the sound's intensity.
Moreover, PPy, PV, and SST cells showed an increase in noise correlations, which became particularly evident as the stressor became chronic. The combination of reduced proportional activity during sound presentation and increased noise correlations can significantly impact sound perception.
Repetitive stress-induced changes in cortical activity may impair loudness perception in mice.”
Mice exposed to repetitive stress were also subjected to a behavioral task. During this task, they received a conditional award for correctly selecting whether a sound was low or high intensity. Under repetitive stress, sounds that were previously categorized as loud were more frequently reported as soft, thus indicating a shift in the mice's perception of loudness.
Conclusions
The current study provides evidence for a possible mechanism by which repetitive stress alters auditory processing, ultimately reducing loudness perception. Importantly, this effect becomes increasingly apparent as exposure to the stressor becomes chronic.
These observations suggest an adaptive strategy: a reduced response to auditory stimuli allows the brain to conserve cognitive resources. Although repetitive stress may lead to greater arousal and vigilance, the study findings suggest that stress may lead to a selective focus on visual or tactile stimuli rather than auditory sources.
Journal reference:
- Bisharat, G., Kaganovski, E., Sapir, H., et al. (2025). Repeated stress gradually impairs auditory processing and perception. PLOS Biology. doi:10.1371/journal.pbio.3003012.