Blog #3: Research Round 1

Inquiry Question: How does the brain relate to hearing and why do certain sounds make our skin “crawl”?

Round 1 Research: What is the brain’s role in hearing?

• The ear detects and delivers the sound information; the brain interprets these sounds and give them meaning (Discover Hearing, n.d.).
• The ears’ role (Discover hearing, n.d.):
  • The ears contain microscopic hair cells that respond to different sound based on pitch or frequency.
  • When soundwaves travel into our inner ear, electric nerve impulses are delivered through the auditory nerve to the brain to be filtered and translated.
  • Damaging the hair cells in the cochlea can lead to hearing loss.
    • Depending on which hair cells are damaged and the seriousness of the damage, the degree of hearing loss and impacted frequencies vary.
    • Aging and long-term exposure to loud noise can damage hair cells and result in hearing loss.
• The brain’s role (Discover Hearing, n.d.):
  • The auditory cortex in the brain recognizes the electric impulses sent by the ears and transform them into meaningful sounds.
  • The auditory cortex also processes the volume of sounds and determine where they are coming from.
  • The brain filters different sounds around us and allows us to focus on the sound we want to listen to.
    • In a room full of people, we can hear the television.
  • The brain also allows us to increase the volume of our own voice when we are in a loud room and reduce the loudness when we are speaking in a library.
  • The thalamus in the brain determines if sounds signal the presence of a threat.
    • Ex. Fire alarm, screaming, loud bang
    • These sounds may trigger an emotional and instinctive response.
  • Facial expressions and hand gestures are processed by the prefrontal cortex in the brain to add context and provide a deeper understanding of sounds.
• With hearing loss, the brain is receiving incomplete or weak signals from our inner ear. This means the brain will try to fill in the missing information and create meaning, leading to fatigue and exhaustion as it is working harder all the time (Discover Hearing, n.d.).
  • The brain can adjust to hearing aids.
  • Long-term hearing loss can contribute negatively to our mental health.
    • Ex. depression, dementia, and feelings of isolation.
• Path of sound waves (Gallun & Saunders, 2018):
  • Sound waves enter the ears then travel down the ear cannel to the inner ear.
  • Sound waves are turned into electrical signals by inner ears.
  • The auditory nerves send the signals to the brain.
• Different areas in the brain are responsible for different jobs (Gallun & Saunders, 2018).
  • Some compare signals to determine where sounds are coming from.
  • Some decode or process language and music.
• The brain turns the sound signals into words, sentences, and ideas (Gallun & Saunders, 2018).
  • This can happen in a few tenths of a second.
• The brainstem of the brain determines where a sound is coming from. It considers (Gallun & Saunders, 2018):
  • Which ear received the louder sound
  • Which ear the sound arrived first.
  • The brain makes a mental picture of the surrounding based off the above two reasons.
• Each of the central auditory areas process different aspects of environmental sounds (Hamel, Peterson, & Reddy, 2022).
  • Attenuation (intensity of sound): processed within the auditory system by neurons, which fire action potentials at different rates depending on the intensity of sounds
  • Location of sound: processed within the superior olivary complex by comparing differences in attenuation and timing of inputs from both ears.
    • Sound is middling (front or back of head) – reach ears at same time
    • Right or left of midline – delay occurs between inputs for both ears
  • Determine the more important sound: processed by combination-sensitive neurons that either enhance or inhibit responses to two or more sounds with a specific temporal delay.
• The outer ear is responsible for collecting sounds (Audiology First, n.d.).
• Sound waves are turned into mechanical vibrations once they enter the ear canal. Travelling through a combination of bones and fluid, they then reach the inner part of the ear (Audiology First, n.d.).
• The mechanical vibrations are turned into electrical signals by the inner ear. They are then passed to the brain through auditory nerve (Audiology First, n.d.).
• In the years we have been alive, our brain has been trained to focus on and recognize the sounds that are important for communication, safety, and comprehension (Audiology First, n.d.).
• When the brain receives signals, it (Audiology First, n.d.):
  • Comprehends speech
  • Filters unwanted sounds
  • Focuses on desirable sounds
  • Interprets new or unfamiliar sounds
• With hearing loss, the brain receives weak or incomplete electrical signals. But due to the ears of experience, the brain can fill in the gaps (Audiology First, n.d.).
• Some effects of hearing loss (Audiology First, n.d.):
  • Exhaustion – brain is always filling the gaps.
  • Social isolation – tiring to try to follow conversations
  • Anxiety and depression – brainpower are exhausted to process weak sound signals
  • Dementia – may be a result of brain exhaustion or social isolation
• Sound from ear to brain (BrainFacts/SfN, 2012):
  • The external ear – the pinna and the external auditory canal – collects sound waves.
  • These sound waves are funneled to the tympanic membrane (eardrum) to make it vibrate.
  • The malleus (hammer) sends the vibration to the incus (anvil)
  • The stapes (stirrup) receives the vibration from the incus.
  • Mechanical vibrations are converted to electrical signals by hair cells.
  • Auditory nerves carry the signals to the brain step.
  • Information is sent to the auditory cortex by nerve fibers. Sounds are to be perceived here.
• For most people, the left side of the auditory cortex perceives and produces speech (BrainFacts/SfN, 2012).
  • Damage to the left side (ex. Stroke), can result in being able to hear but unable to understand language.
• Conditions that can impact our hearing (Cleveland Clinic, 2020):
  • Aging – more exposure to sounds, environmental toxins, medicines, health issues.
  • Damage/trauma – pushing cotton swabs can result in a punctured eardrum
  • Disease – ex. Diabetes can result in hearing issues by decreasing blood supply to the ear
  • Medication – drugs used to treat cancer, infections, and heart disease can damage hearing.
  • Sound exposure – exposure to sounds that are too loud for too long can damage structure in inner ear.
  • Ear wax – too much wax can block sound from getting to eardrum.
• Auditory deprivation: brain deprived of sound such as from untreated hearing loss (Burry, 2020).
  • Brain lacks ability to understand and process information because of the lack of stimulation.
• If hearing lost is left untreated, the section of the brain that normally is responsible for hearing will do other tasks (Burry, 2020).
  • Not using the part of the brain leads to atrophy/shrinkage.
• The auditory part of the brain needs stimulation to stay sharp (Burry, 2020).

References

Audiology First. (n.d.). How the brain hears. Audiology First. Retrieved October 21, 2022, from https://www.audiologyfirst.ca/how-the-brain-hears

BrainFacts/SfN. (2012, April 1). Hearing. BrainFacts.org. Retrieved October 21, 2022, from https://www.brainfacts.org/thinking-sensing-and-behaving/hearing/2012/hearing

Burry, M. (2020, December 22). Why untreated hearing loss is bad for your brain. Healthy Hearing. Retrieved October 21, 2022, from https://www.healthyhearing.com/report/46306-Hearing-loss-auditory-deprivation

Cleveland Clinic. (2020). Hearing system. Cleveland Clinic. Retrieved October 21, 2022, from https://my.clevelandclinic.org/health/articles/17054-hearing

Discover Hearing. (n.d.). What is the brain’s role in hearing? Discover Hearing Centre Edmonton. Retrieved September 30, 2022, from https://www.discoverhearing.ca/what-is-the-brains-role-in-hearing

Gallun, F., & Saunders, G. (2018, June). PDF. Portland; National Center for Rehabilitative Auditory Research.

Peterson, D. C., Reddy, V., & Hamel, R. N. (2022, January). Neuroanatomy, Auditory Pathway. National Library of Medicine. Retrieved October 21, 2022, from https://www.ncbi.nlm.nih.gov/books/NBK532311/

For the next research round, my topic will be: What is the “skin crawling” feeling? How is it generated? What is the process in our body that makes us feel this way? After research round #1, I understand the close relationship between the brain and our ears, and how we hear and process sounds. With this background understanding, I can now research more specifically on the “skin crawling” effect when we hear sounds. I want to find out what this feeling is, why we have this feeling, and if the processing in the brain is related to it. This feeling seems to be a universal feeling most people have. For example, the sound of nails scratching on a black board is “skin crawling.” Therefore, I also want to know why the discomfort is universal. Is it related to a certain type of sound? Or the way a section of our brain works? All the above will help me dig deeper into my inquiry question and provide a more specific answer, as well as leading to research round 3.