In this study, the researchers asked 13 volunteers to listen to sounds ranging from a knife on a bottle to a babbling brook, and rate them from most unpleasant to most pleasant.

By observing the responses to each noise, coupled with the brain imaging, researchers were able to better understand how the brain responds to particular sounds.

Two Parts Of The Brain Work Together

The fMRI’s showed that when we hear unpleasant sounds, the area of our brain that processes emotions (the amygdala) adjusts the response in the part of our brain that processes sound (the auditory cortex). The amygdala’s effect on the auditory cortex leads to a negative reaction to the sounds we instinctively don’t like.

Study author Dr. Sukhbinder Kumar says, “It appears to be something very primitive kicking in. It’s a possible distress signal from the amygdala to the auditory cortex.”

Heightened Perception Of Unpleasant Sounds

The amygdala’s effect on the auditory cortex was found only for sounds that the participants found most unpleasant. When an unpleasant sound was perceived by the amygdala, it led to a heightened perception of the sound by the auditory cortex, which is is perceived as unpleasant. This didn’t happen with soothing sounds like the babbling brook.

Our Ears Are Sensitive To Certain Sounds

When they analyzed the sounds used in the study, the researchers found that sounds in the 2000 to 5000 Hz range were perceived as the most unpleasant. Dr. Kumar noted,“This is the frequency range where our ears are most sensitive. Although there’s still much debate as to why our ears are most sensitive in this range, it does include sounds of screams which we find intrinsically unpleasant.”

An Important First Step

This research is an important step forward in understanding and helping to treat conditions that make people sensitive to certain sounds, such as tinnitus, migraine headaches or autism.