NOISE and STRESS

Human infants are all ears. Yes! they are very conscious of sound and focus on every word that they hear, hence 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 16- 20 months old, infants react strongly to distress sounds from other infants. Children in noisier neighborhoods experience higher overnight levels of the stress hormone “cortisol”, marginally higher resting systolic blood pressure, and greater heart rate reactivity to a stress test. These are all signs of modestly elevated physiological stress.

Compared to kids from quieter neighborhoods, children living near airports or busy highways tend to have lower reading scores and develop language skills more slowly. Psychiatric hospitalizations are higher in noisy communities. Bad moods, lack of concentration, fatigue, and poor work performance can result from continual exposure to unpleasant noise. It elevates psycho-physiological factors and triggers more symptoms of anxiety and nervousness. Therefore, chronic exposure to nearby sounds from roads and train lines are a concern.

Chronic low-level noise also negatively influences the brain and behavior. Whether from the road or in the office, low-intensity noise has a subtle yet insidious effect on our health and well-being. Noise at home or school can affect children's ability to learn. Over 10 million people have hearing loss because of "toxic noise" in the workplace. Although preventable, toxic noise is the most common occupational disease and the second most self-reported occupational injury.

A disorder in the electrical system of the heart, known as the Long QT Syndrome (LQTS), is a life threatening disorder that can be triggered by a loud noise. In people with LQTS, the electrical recovery of their heart takes longer than normal after each heart beat. Acoustic stress such as awakening because of a loud noise can trigger an episode. Symptoms usually occur during physical exertion or emotional excitement like anger, fear, or startle. Common examples of startle events include sudden noise, like sirens, the telephone, and the alarm clock.

Stress can even aggravate a number of psychiatric disorders, many of which are associated with the prefrontal cortex (PFC), the area of the brain unique to humans. Chronic over-secretion of stress hormones adversely affects brain function, especially memory. Too much cortisol can prevent the brain from laying down a new memory, or from accessing already existing memories. Sustained stress can damage the hippocampus, the part of the limbic brain which is central to learning and memory.

Cortisol also interferes with the function of neurotransmitters, the chemicals that brain cells use to communicate with each other. Excessive cortisol can make it difficult to think or retrieve long-term memories. That is why people get perplexed and confused in a severe crisis. Their mind goes blank because the neurotransmitters are numbed. For example, a person can’t remember where the fire exit is in case of a bomb explosion and the chaotic environment developed in a building.

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 paralyze animals. Even experienced human trainers are stunned. 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?