Who still remembers cringing from the high-pitched screeches of your grade school teacher pressing down on chalk a tad too hard? For those of you with younger siblings, what about the time when you were rudely awakened up in the middle of the night from the baby’s bloodcurdling screams?
Sukhbinder Kumar, a neuroscientist from Newcastle University, recently revealed the neurological explanation that accounts for the negative emotions we experience after hearing unpleasant sounds.
A total of 13 volunteers were recruited for the study. They were asked to rate the pleasantness of 74 sounds in relation to each other. The sounds ranged from knives on bottles and female screams to water flowing and babies laughing.
Next, the brains of the participants were scanned using functional magnetic resonance imaging (fMRI) while they listened to each sound. Relative activity in the brain was then compared to the subjective ratings of pleasantness.
Results showed a correlation between the amygdala and the auditory cortex. Moreover, there was a positive relationship between the activation of these areas and the degree of unpleasantness of the sounds.
The auditory cortex, located in the temporal lobes to the lateral sides of the brain, is the primary area that processes sounds. Activity in this area underlies our awareness and perception of auditory stimuli.
The amygdala is a structure of the limbic system that plays a role in processing memories and emotional reactions. Specifically, the amygdala is activated when we are experiencing fear and other negative emotions.
In this study, the amygdala was shown to modulate the sensory stimuli received by the auditory cortex, thereby resulting in the unpleasant experiences we are used to feeling in response to unpleasant sounds, such as fingernails on a chalkboard.
Moreover, results show that sounds between 2,000 and 5,000 Hertz were generally found to be unpleasant as humans are most sensitive to this frequency range. However, the functional and evolutionary significant of this sensitivity remains unclear.
This study serves as a foundation for future research in auditory processing and associated disorders, such as misophonia and autism. Those with misophonia show decreased tolerance to certain sounds, such as breathing or some consonants. People with autism spectrum disorders are also shown to have heightened sensitivity to auditory stimuli.
The preferential activation of the amygdala and the cortex in response to specific sounds holds important implications for other neurological disorders that affect hearing as well. For instance, those with migraines commonly show increased perception of sounds.
Based on these findings, scientists can continue to develop a better understanding and potential treatments for disorders that affect auditory processing.
