From Alarms to Birdsongs: How Your Brain Reacts to the Sounds of Daily Life
- skduo9
- Jul 3
- 5 min read
By: Sucharita Desu
Sound is a part of everyday life. From your morning alarms to the music you listen to, every sound travels as a wave that vibrates air particles. Sound waves can be described by two main characteristics: frequency (measured in Hertz, Hz) and amplitude (measured in decibels, dB). In other words, this is what we call pitch and volume/loudness respectively. When sound waves reach your ear, they are captured by the pinna and funneled through the ear canal, eventually vibrating your tympanic membrane, the eardrum! From there, the sound waves travel as mechanical vibrations through the three tiniest bones in your body known as the ossicles. Together, the malleus, incus, and stapes are responsible for amplifying sounds by 20 to 30 times before pushing the sound into the fluid-filled cochlea for frequency analysis. Inside the cochlea, the cells follow a tonotopic organization where the base of the spiral structure responds to high frequencies and the apex/tip responds to low frequencies. Specifically, the cochlea is filled with inner hair cells that convert the mechanical vibrations of the sound waves into an electrical signal for neural processing. At the same time, the outer hair cells help amplify the sound so you can hear it clearly.
To travel up to the central nervous system, the inner hair cells synapse onto the spiral ganglion neurons and transmit a signal. These neurons form the cochlear nerve, sometimes referred to as the auditory nerve, and synapse in the brainstem to start processing the sound. First, at the cochlear nucleus, the sound duration, intensity, and frequency are decoded. Then, at the superior olivary complex, auditory information from both ears is integrated and localized. Integration of auditory information is also performed at the inferior colliculus before the signal is sent to the medial geniculate nucleus of the thalamus to be relayed to higher processing areas of the brain. One of those areas is the primary auditory cortex in the superior temporal gyrus. Here, the sound is processed based on its characteristics and sent to higher auditory areas such as Wernicke’s area (responsible for speech), right superior temporal lobe (involved in music), amygdala (for emotional processing), prefrontal cortex (attention), and hippocampus (memory).
NOTE: As auditory information passes from your inner ear structures, like the cochlea, through the afferent nerves, and in the higher processing areas of the brain, the tonotopic map of sound is preserved.
So, now what? What does our brain really do or think when we hear a sound? While it is hard to cover every single sound of the universe in this article, we can talk about sounds we hear in our daily life. One example is a blaring alarm that wakes you up in the morning. This annoying sound is engineered with the purpose of cutting through your sleep and triggering your brain’s arousal systems instantly. This type of sound is considered a salient, urgent signal; it is something like a mild threat and activates the sympathetic nervous system (your fight-or-flight response). If you were measuring your brain activity through an electroencephalogram (EEG) during your alarm, the signal would be characterized by a large, sharp negative deflection, followed by a positive bump. This is your brain’s way of saying “Wake up, something just happened.” The shift in your attention can be seen through positive peaks in the EEG signal, indicating your brain is trying to “turn” towards the sound. Lastly, you would see a suppression of alpha brain waves (8 to 12 Hz) as your brain wakes up coupled with an increase in beta (13 to 30 Hz) and gamma (>30 Hz) brain waves. This indicates that your brain is alert, processing and integrating sensory information. Physiologically, the auditory cortex processes the frequency and pattern of the sound, while your amygdala classifies it as emotionally significant and perhaps unpleasant. As a result of the sound, nuclei in the brain stem (i.e. locus coeruleus) release norepinephrine to increase alertness and attention, while the hypothalamus and adrenal glands increase cortisol to increase heart rate and blood pressure. Together, your body and brain are shifted from sleep-mode to awake and turning off your alarm. Other sounds that share similar characteristics and responses include phone notifications, sirens, car horns, crying babies, a loud bang or even an unexpected knock on the door.
The opposite to this response would be parasympathetic nervous system activation. This can be caused by listening to water sounds or birdsong, which are much lower in frequency, rhythmic, and predictable. These types of noise are known for lowering stress, as they switch your body into a rest-and-digest mode. On an EEG, this looks like increased alpha brain waves, stable and low beta waves, reduced positive peaks, and lower amplitudes for the negative deflection and positive bump. Within your body, listening to the rain, or the flow of water through a stream has been found to reduce cortisol, heart rate, and blood pressure. It also modulates amygdala activity, giving control to your prefrontal cortex to help improve emotional regulation and enhance calmness. Similarly, birdsong is restorative to your mind, helping improve mood and reduce physiological arousal, especially after high stress situations. They also help with attention recovery and cognitive performance, bringing a sense of safety and clearing your mind. This can also be seen with other sounds of nature, such as wind blowing through trees, ocean waves, and other animal noises. Thus, they are heavily used in therapy and mental health interventions (i.e. meditation).
There are also noises that can be right in between calming and alerting, such as white noise. This makes it so that your brain’s reaction depends on external cues, such as context, predictability, as well as individual differences. White noise consists of a broad range of frequencies, is constant, and is unpatterned. To the brain, it is basically considered a low-information input. Since there are no changes in the sound, the auditory cortex will stop actively listening to it and therefore reduce arousal, mind-wandering, and emotion. White noise can also help mask unpredictable noises in your environment, such as the sounds of traffic. This can help induce a feeling of calm, reducing your heart rate, while also increasing your focus. However, it is important to note that some people are more sensitive to certain sensory stimuli; to them, white noise is irritating rather than neutral. Other variants of white noise include pink noise and brown noise.
In the end, our everyday soundscape can shape us more than we realize. Our brains are constantly listening for cues of danger or safety, and every sound acts as a message. By understanding our neurological responses, we gain the ability to choose what we surround ourselves with and create a personal and suitable environment for our mind and body. To learn more about auditory processing in the brain and the types of sounds, check out these recommended videos:
Image credits: Unsplash
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