Do the screams of a siren or the shrill cry of a peacock send you into flight or fight mode? Does the sudden honk of a vehicle make you jump? If so, you are not alone. The effects of harsh sounds can seem intolerable to some people. In fact, this is the reason most alarms are so annoying.
Alarm manufacturers intentionally use tones with fast-paced, repetitious sounds that have the effect of putting us on alert. Neuroscientists at the University of Geneva (UNIGE) as well as Geneva University Hospitals (HUG) in Switzerland have spent time researching the reactions that people have to a varied range of sounds.
With a goal of identifying the point that test subjects determined these frequencies to be objectionable, scientists explored the areas of the brain that reacted to different frequencies. By having them listen to sounds repeatedly from 0 to 250 Hz at intervals closer together each time, researchers at UNIGE asked participants to determine the point where the sounds went from several intermittent sounds to a solid, continuous one.
With the responses they got, the scientists found that at around 130 Hz participants heard only one continuous sound. This prompted the question of why the brain determines harsh sounds as obnoxious. Keeping that in mind, they requested that the test participants listen to different frequencies. They were instructed to categorize them from 1 to 5, with 1 being tolerable and 5 being obnoxious.
According to Luc Arnal, who is a researcher at the Department of Basic Neurosciences at UNIGE’s Faculty of Medicine, “The sounds considered intolerable were mainly between 40 and 80 Hz, i.e. in the range of frequencies used by alarms and human screams, including those of a baby. That’s why alarms use these rapid repetitive frequencies to maximize the chances that they are detected and gain our attention.”
Armed with this knowledge, neuroscientists worked to figure out why the brain reacts to these as sounds as intolerable. Pierre Mégevand, a neurologist and researcher in the Department of Basic Neurosciences in the UNIGE Faculty of Medicine and at HUG reported, “We used an intracranial EEG, which records brain activity inside the brain itself in response to sounds.”
For sounds that are detected as one long continual sound, the intracranial EEG showed that there was activity in the auditory cortex, which is located in the upper temporal lobe. Mégevand stated, “This is the conventional circuit for hearing.”
The sounds that participants determined were intolerable (such as the ones they reported between 40 Hz and 80 Hz) resulted in a constant reaction that also involved a number of cortical and subcortical areas that are not normally involved in the traditional auditory system.
To this, Arnal responded, “These sounds solicit the amygdala, hippocampus, and insula in particular, all areas related to salience, aversion, and pain. This explains why participants experienced them as being unbearable.” He was reportedly surprised about the fact that these regions had something to do with sound processing.
Researchers were unable to find previous data that supported their findings that sounds between 40 Hz and 80 Hz had ever been determined to drive these same neural networks, though for many years these same frequencies have been used in various alarm systems.
According to Arnal, “We now understand at last why the brain can’t ignore these sounds,” says Arnal. “Something in particular happens at these frequencies, and there are also many illnesses that show atypical brain responses to sounds at 40 Hz. These include Alzheimer’s, autism and schizophrenia.”
Neuroscientists anticipate that further research into the topic will show why these areas are motivated by this specific range of frequencies. They hope to learn if early detection is possible for illnesses such as Alzheimer’s, autism, and schizophrenia.
According to a study listed online at PMC US National Library of Medicine National Institutes of Health loud noises can bring about certain neuropsychiatric responses like the following:
- Emotional stress
- Psychiatric disorders
These can be responsible for changes to the hypothalamic pituitary axis (HPA) which is associated with how the body reacts to stress. Sudden, loud, harsh noises can create stress, which our body responds to almost instantaneously in the sympathetic nervous system. It begins the process of secreting epinephrine and norepinephrine, which are responsible for the changes you would normally experience when frightened or stressed such as an increase in heart rate and excess perspiration.
Within seconds the HPA axis is alerted and the hypothalamus reacts to signals such as raised norepinephrine levels. It then begins the secretion of corticotropin, a hormone released during the stress response. The pituitary gland responds by secreting adrenocorticotropic hormones which in turn triggers the release of cortisol.
Cortisol is known to increase the blood pressure as well as the cardiac output which provides more blood to your muscles in the event the stressor needs to result in physical exertion, such as running for your life.
When considering that the sound of sirens on emergency vehicles, tornado sirens, or even alarm clocks are designed to alert and potentially raise attention, it’s easier to understand why. When armed with this information, people can gain a better understanding of the reasons behind the discomfort and even fear that surrounds these loud and intolerable sounds.