[A series of harsh sounds.]

Not nice to listen to. But what makes such noises unbearable?

Part of the answer is that the brain appears to be hardwired to be alarmed at, for example, alarms and other shrill noises.

Researchers scanned the brains of 16 participants as they listened to a range of sounds, and asked them to rate the sounds from unpleasant to less unpleasant. Activity in both the auditory cortex and the amygdala varied directly with the subject’s ratings.

The auditory cortex is where a sound’s acoustic features are processed. But it is the amygdala—the small part of the brain in charge of emotional memory—that encodes those features and triggers the negative reaction to unpleasant sounds. And this reaction from the amygdala is delivered back to the cortex making us extremely sensitive (acoustically) to such sounds.  This interaction between the auditory cortex and amygdala happens so fast as to seem instant.

The researchers hope to test this model next with purely pleasurable sounds, as well as other types of negative sounds, including bad words, like [bleep] and [bleep] and [bleep.]

—Christie Nicholson

[The above text is a transcript of this podcast.]