If you suffer from chronic stress, your brain will change the way it processes sounds – at least if you’re a mouse. Is this why too many Israelis shout under pressure?
According to new research conducted on adult mice aged 16 weeks at Ben-Gurion University of the Negev (BGU) in Beersheba, sounds need to be louder during chronic stress to trigger similar responses.
Many of us Israelis – especially in the last year or two during these difficult times – suffer from repetitive stress, which, in any case, is a common feature of modern life worldwide.
Unfortunately, it is a major risk factor for psychiatric and sensory disorders. Despite the prevalence of perceptual abnormalities in these disorders, little is known about how repetitive stress affects sensory processing and perception.
Chronic stress is known to affect learning and decision-making, but could it also affect how we hear? Biology researcher Dr. Jennifer Resnik of the university’s life sciences department and her team set out to find whether stress influences basic brain functions such as processing sounds.
How do our brains deal with stress?
“We know that chronic stress can modulate attention and learning, but there has been little research on how our brains process neutral sounds under chronic stress,” she explained. Her findings have just been published in PLOS Biology under the title “Repeated stress gradually impairs auditory processing and perception.”
Resnik was born in Argentina, which may explain why she speaks very fast but not very loudly. She made aliyah in 1995, received her bachelor’s degree at Tel Aviv University, and her master’s degree and PhD at the Weizmann Institute of Science in Rehovot.
She then completed a post-doctorate as a biologist at Harvard Medical School for five-and-a-half years before coming home to Beersheba.
“We think our findings are relevant to people because the human auditory system closely resembles that of mice. Prior research has focused on the effects of unpleasant sounds, but no studies have explored how chronic stress influences the perception of everyday sounds – an area we are very interested in,” she continued.
The researchers found that chronic stress didn’t affect the ear itself. Instead, they discovered a clear effect of chronic stress on sound responses in the auditory cortex that develop over time. Sounds at moderate decibel levels triggered significantly weaker reactions as the stress persisted, while the mice maintained strong responses to higher decibel sounds.
Resnik explained that this effect occurs because stress elevates the brain’s “background noise.” In stressed mice, she noted, “We observed an increase in baseline (spontaneous) activity in excitatory cells of the auditory cortex.”
In a brain without this heightened baseline activity, signals from the ears stand out more clearly. However, in a stressed brain, the difference between the signal and the surrounding neural activity is reduced.
As a result, Resnik said, “the brain becomes less sensitive to mid-level sounds. Think of it like this – when you’re chronically stressed, your children might have to speak louder to get your attention. Interestingly, responses to high sound levels appear to be preserved. No matter what, the brain still reacts when a sound is loud enough. So, if your kids shout, you’ll hear them just as clearly, regardless of stress.”
The researchers also discovered that this effect may be driven by one type of inhibitory cell becoming vastly more active under conditions of repeated stress and suppressing other cells. They found that somatostatin (SST) cells – well-known neuropeptides expressed throughout the brain – began to fire much more strongly when a sound was played.
The activities of pyramidal cells – a type of multipolar neuron found in areas of the brain including the cerebral cortex, the hippocampus, and the amygdala – and parvalbumin (PV) interneurons that allow them to precisely control local circuitry, brain networks, and memory processing – dropped.
That may explain the dampening of sounds, Resnik said.
“Our research suggests that repeated stress doesn’t just impact our reactions to emotionally charged stimuli; it may also alter how we respond to everyday neutral stimuli, using mice to uncover how stress might alter the way sounds are interpreted,” she concluded.
She and her team of students have planned follow-up experiments to try reversing the effects of chronic stress on the brain. “Specific types of inhibitory cells increase their activity during repetitive stress. We are trying to reduce their activity to reverse the effects of stress."