Everyday Noises Are Making Our Brains Noisier

November 1, 2021

Take a walk on a busy avenue and you hear either traffic whizzing by or creeping in a honk-laden crawl. Add the hissing of pneumatic bus brakes, distant sirens, the boom-boom of overloud car stereos, the occasional car alarm, music coming from shops you pass, the beeping of a reversing delivery truck. All are part of the fabric of city life.

These sounds do not meet or exceed the generally accepted threshold of “unsafe.” They are not novel and alerting. They are ongoing and have generally consistent acoustic properties over time. These are the sorts of sounds most would consider “background noise.” For this reason, we tend to ignore them. We tune them out. But are we really tuning them out, or are we simply living our lives in a constant state of alarm?

We have all experienced not noticing a sound until it goes away. Often it is an air conditioner or an idling truck. The air conditioner cycles off or the ignition is cut, and suddenly we “hear” the silence. And we sigh in relief. We momentarily revel in the peace until it starts up again or is replaced by the next aural annoyance. If our ears are not being damaged and we can mostly tune it out, should these noises concern us? We should indeed notice it and be concerned for the sake of our brains.

A noisy environment has many underrecognized negative impacts that have little to do with hearing per se. Chronic noise exposure, such as might be experienced by individuals who live near an airport, can lead to an overall decrease in perceived quality of life, increased stress levels along with an increase in the stress hormone cortisol, problems with memory and learning, difficulty performing challenging tasks, and even stiffening of blood vessels and other cardiovascular diseases.

According to the World Health Organization, noise exposure and its secondary outcomes such as hypertension and reduced cognitive performance are estimated to account for an astounding number of years lost due to ill health, disability, or early death.

Noise disturbs learning and concentration. Students attending public schools in New York City had markedly different reading outcomes depending on whether their classroom was on the side of the school that fronted a busy elevated train track or on the other side of the school, which was shielded from the train noise. Students on the noisy side lagged 3 to 11 months behind their peers in reading.

In the wake of these findings, the New York Transit Authority installed rubber padding on the railroad tracks near the school and the Board of Education installed noise-abatement material in the noisiest classrooms, together reducing noise levels by about 6 to 8 decibels. The reading-level difference soon vanished.

The effect of noise is not limited to auditory or language tasks like reading. In one experiment, subjects were asked to track a visual target, a moving ball, on a computer screen with a mouse. Meanwhile, other balls were simultaneously roving around on the screen. Participants who had experienced long-term noise exposure as part of their occupation had a more difficult time with the task, especially when the task itself was accompanied by random noises; they were slower and unable to keep as close to the target ball.

In Why We Sleep, University of California, Berkeley sleep scientist Matthew Walker calls the lack of proper sleep “the greatest public health challenge we face in the 21st century.” Sleep is becoming more recognized as crucial for our health, as it affects our cardiovascular system, our immune system, and our ability to think. Noise is one of the biggest culprits keeping us from a good night’s rest.

Noise—even at fairly low sound levels—has a harmful impact on quantity and quality of sleep. Noise keeps us awake longer and awakens us earlier. While sleeping, noise in the environment affects the quality of sleep, prompting body movements, awakenings, and increased heart rate. Traffic noise can shorten periods of REM (dream) and slow-wave (deep) sleep, and diminish one’s perception of the restfulness of a night’s sleep.

In our waking lives, the insult of “safe” noise to the sound mind can be especially pernicious for children. Children are masters of language learning. Parents are gobsmacked at the short amount of time that elapses between observing their child say their first word to their speaking in full sentences. Sound to meaning connections are formed with great rapidity. Children cannot help learning the languages they are exposed to—even more than one. But what if the sounds children are exposed to at this critical age are meaningless?

This question is difficult to address in humans because it is impossible to control noise levels adequately in a real-world setting. However, we can answer questions like this in animal experiments. By controlling the duration, intensity, and quality of sound exposure, it is possible to get a direct look at how the electrical signals—the currency of the nervous system—in the brain are affected. Just what happens to our sound minds when we are exposed to “safe” noise? And are these effects transient or permanent?

Noise exposure accounts for years lost due to ill health, disability, or early death.

Typically, by adulthood, the auditory cortex of a rodent is organized tonotopically. 

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