“The squeal of chalk on a blackboard” feels painful to almost everyone. Scientists speculate that nails screeching on a blackboard sounds like primate distress calls.
But for many people with sensory processing difficulties, the hiss of running water or the roar of a vacuum cleaner can sound just as unpleasant as nails on a blackboad. So maybe it makes sense to look at just how typical brains decide nails on the chalkboard is such a painful sound. Maybe the same equipment is involved in autistic sensory pain to noises.
To learn about the processing of painful (“aversive”) sounds, we turn to:
A Dynamic System for the Analysis of Acoustic Features and Valence of Aversive Sounds in the Human Brain
Sukhbinder Kumar, Katharina von Kriegstein, Karl J. Friston,and Timothy D. Griffiths
Researchers had previously found that a spectral analysis of a sound could predict its relative unpleasantness. Now they embarked on an even greater adventure — to see if this spectral analysis could be used to predict functional MRI data of people listening to painful sounds.
First fMRI was acquired from 13 subjects as they listened to 74 different sounds. Subjects rated each sound on its unpleasantness.
Analysis revealed activity in both amygdala were correlated to the acoustic features, but only the right basolateral amygdala was found to be correlated to the unpleasantness of the sound. The authors discuss how the basolateral nucleus acts as the amygdala’s “sensory interface”, receiving signals from the both the auditory thalamus and the association areas of the auditory cortex“.
Acoustic features correlated with activity in the auditory cortex (specifically the anterior Superior Temporal Gyrus and the “upper bank” of the Superior Temporal Sulcus). The unpleasantness of the sound was correlated only with the right Superior Temporal Gyrus.
Researchers conclude that the audio signal is first processed in the auditory cortex (superior temporal gyrus), after which it is passed to the amygdala which evaluates the signal’s unpleasantness. That value judgment is the passed back to the auditory cortex.
Why do the vacuum cleaners or showers elicit fear or pain in people with sensory issues? If it’s for similar reasons to chalkboard scraping, then perhaps we should look to the right basolateral amygdala.