Right to Quiet Society Noiseletter
Spring 2008 - page 2

Noise causes detrimental stress

The Franklin Institute Online has numerous interesting articles posted, many of which explain how adversely noise can affect our health. Following are just a few samples.
We have a link to the F.I. website at <www.quiet.org/links> or visit <http://www.fi.edu/learn/brain/images>
“Attack of the Adrenals”—
a Metabolic Story

The ambulance siren screams its warning to get out of the way. You can’t move your car because you’re stuck in a bumper‑to‑bumper traffic jam that reaches as far as the eye can see. There must be an accident up ahead. Mean-while, the road-construction crew a few feet from your car is jack‑hammering the pavement. You are about to enter the stress zone.

Inside your body the alert goes out. "Attention all parasympathetic forces. Urgent. Adrenal gland missile silos mount-ed atop kidneys have just released chemical cortisol weapons of brain destruction. Mobilize all internal defences. Launch immediate counter‑calm hormones before hippocampus is hammered by cortisol."

Hormones rush to your adrenal glands to suppress the streaming cortisol on its way to your brain. Other hormones rush to your brain to round up all the remnants of cortisol missiles that made it to your hippocampus. These hormones escort the cortisol remnants back to Kidneyland for a one‑way ride on the Bladderhorn. You have now reached metabolic equilibrium, also known as homeostasis.
Our Startle Response to Noise
Human infants are all ears. They are very conscious of sound and focus on every word they hear, so they can learn to speak. Loud noises trigger a "startle response"— large movements of the baby's limbs and torso – even while in the womb. Until 18 months old, infants react strongly to distress sounds from other infants.

Crucial to survival, this instinctual reaction to noise enables us to go from a deep sleep to a quick sprint in a matter of seconds. . . or to do battle with surprising strength. Today, however, our stress response is getting knee‑jerked around by all the bells and whistles of modern civilization. From the clatter and jar of diesels and dump trucks, to chest‑thumping teenage car tunes, noise is almost impossible to block. Its very uncontrollability further adds to the stressful impact.
Noise Stress and Brain Function‑Study
Stress can exacerbate a number of psychiatric disorders, many of which are associated with the prefrontal cortex (PFC), the area of the brain unique to humans. A Yale University study looked at the effects of noise stress on brain function in monkeys. Results indicate that stress impairs PFC cognitive function through its influence on dopamine, a key neurotransmitter that's involved in many brain disorders, including ADHD and Parkinson's disease.


The researchers think that "stress may take the PFC 'off-line' to allow more habitual responses . . . to regulate behaviour. This mechanism may have survival value, but may often be maladaptive in human society, contributing to the vulnerability of the PFC in many neuropsychiactric disorders."
Responding to Noise We Cannot Hear—Study
Even sounds you can't hear can have a powerful affect on your nervous system. One example is the "infrasound" in the roar of a tiger.

A tiger's intimidating roar has the power to paralyse animals. Even experienced human trainers are stunned. "We suspect that this is caused by the low frequencies and loudness of the sound," says Elizabeth von Muggenthaler, a bioacoustician from the Fauna Communications Research Institute in North Carolina. "Humans can hear frequencies from 20 hertz to 20,000 hertz, but whales, elephants, rhinos, and tigers can produce sounds below 20 hertz."

The shocking power of a tiger's roar is one example of how humans react to a sound they cannot detect with their ears. But what about all the noise generated by our modern world – including the multitude of ultrasounds whose frequencies are above 20,000 hertz and beyond our hearing range?
Tiger Sound‑Study
In the first study of its kind, von Muggenthaler and her colleagues recorded every growl, hiss, chaff, and roar of 24 tigers at the Carnivore Preservation Trust in Pittsboro, North Carolina, and the Riverbanks Zoological Park in Columbia, South Carolina. The bioacousticians found that tigers can create sounds at about 18 hertz, and when tigers roar they can create frequencies significantly below this.

This unheard, low‑pitched infrasound can travel long distances—permeating buildings, cutting through dense forests, and even passing through mountains.
Traffic Noise Increases Stress Hormones in Children  
Even everyday traffic noise can harm the health and well-being of children. In the first study to look at the non‑auditory health effects of typical ambient community noise, it was shown that chronic low‑level noise from local traffic raised levels of stress hormones in children, as well as their blood pressure and heart rates.

"We found that even low‑level noise can be a stressor. It elevates psycho-physiological factors and triggers more symptoms of anxiety and nervousness," says environmental psychologist Gary Evans of Cornell University, an inter-national expert on environmental stress, such as noise, crowding, and air pollution.

Continued on page 3...

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