A recent study published in PLOS Biology has shed light on the effects of chronic stress on sensory processing, revealing how repeated stress impacts sound processing and diminishes the perception of loudness in mice.
Stress and its Impact on Cognitive Functions
Chronic or repetitive stress has long been known to contribute to a range of psychiatric and sensory disorders. Unlike acute stress, which triggers immediate and short-lived responses, repetitive stress has enduring effects even after the original stimulus is removed. This persistent stress leads to changes in the brain’s adaptive responses, affecting both the central and peripheral nervous systems.
Research has previously highlighted the detrimental effects of chronic stress on cognitive functions such as memory, learning, and decision-making. However, less is known about how it influences fundamental cortical activities, particularly sensory processing. Sensory experiences, such as the perception of sound or smell, are often influenced by an individual’s internal state, with stress potentially amplifying the intensity of external stimuli.
In this study, researchers set out to explore how repetitive stress affects sound processing and the perception of neutral sounds by assessing changes in auditory cortex activity and auditory-guided behaviors in mice.
Methodology and Findings
For seven consecutive days, the study subjects—mice—were subjected to 30 minutes of daily restraint stress. The team measured physiological and behavioral stress markers throughout the experiment.
The results showed a significant increase in corticosterone levels, which remained elevated for over an hour following each stress session. As the experiment continued, corticosterone levels before the stress sessions began to rise, a sign of chronic stress. Notably, the mice did not exhibit any signs of habituation to the stressor.
In terms of behavior, the restrained mice displayed reduced activity levels during an open field test, which persisted even after a week of daily stress exposure. Importantly, this mild restraint stress did not significantly alter the expression of glucocorticoid receptors (GR) in the primary auditory cortex.
To assess how repetitive stress impacted sensory processing, the researchers employed two-photon calcium imaging to observe the activity of parvalbumin-expressing (PV) and pyramidal neurons (PPYs) in the auditory cortex of awake mice. The results revealed that, during the stress period, both PPYs and PV neurons significantly reduced their response to sound, especially at moderate intensities.
Interestingly, there was no change in the percentage of PV cells responsive to sound, unlike in the control group of mice that were not exposed to daily restraint stress.
Further analysis revealed that, during repetitive stress, PPY neurons showed increased activity before and after exposure to white noise. This heightened activity varied with the intensity of the sound. Similarly, the expression of somatostatin-expressing (SST) inhibitory cells increased during both pre- and post-sound periods, a pattern comparable to that seen in PPYs and PV cells. Notably, the activity of SST cells showed a larger difference between pre- and post-sound periods under repetitive stress.
Implications for Sound Perception
The study found that chronic stress reduced the activity of PPY and PV cells in response to sound while increasing the activity of SST cells. This shift in neuronal activity is suggestive of a cumulative effect on auditory processing, dependent on sound intensity. Furthermore, the study observed an increase in noise correlations among PPY, PV, and SST cells as the stress exposure became more prolonged.
This combination of reduced activity during sound presentation and heightened noise correlations may play a role in altering the mice’s perception of sound. In behavioral tasks, mice exposed to chronic stress began to misclassify loud sounds as softer, indicating a shift in their perception of loudness.
Conclusion
The study offers new insights into how chronic stress can disrupt auditory processing and reduce loudness perception. As stress exposure becomes prolonged, these changes in sound processing become more pronounced. The findings suggest that the brain may adapt by conserving cognitive resources, decreasing its response to auditory stimuli in favor of other senses, such as visual or tactile inputs. This selective focus might be an adaptive strategy, allowing the brain to prioritize critical stimuli in times of prolonged stress.
Related topic:
Study Links Partner Support to Better Health and Relationship Quality
Broccoli Compound Linked to Improved Blood Sugar in Prediabetes
Air Pollution in Late Pregnancy Linked to Higher NICU Risk
