If you have normal hearing and an amygdala, you can probably tell which of these two songs is “happy,” and which is “scary.”
However, for extreme cases of epilepsy, one treatment is to surgically remove the amygdala, the area of the brain which processes, among other things, the sensation of fear. People who have had this surgery fail to recognize fearful facial expressions. A 1978 study in which experimenters stimulated patients’ amygdalas directly with electrodes caused them to behave as if they were afraid.
But other efforts to induce fear reactions in patients whose amygdalas have been damaged or removed have had mixed results. One study found that people with damage to the amygdala could not recognize fear in faces, but could recognize fear in voices. Some studies measuring healthy individuals found that screams and yells do activate the amygdala, but others have found no impact of fearful speech prosody (the musical aspects of speech) on the amygdala.
A team led by Nathalie Gosselin devised an experiment to clarify the role of the amygdala in music perception. They had a composer create 56 musical excerpts, each designed to express one of four emotions: happiness, fear, sadness, and peacefulness. These excerpts were played for sixteen patients whose epilepsy had been cured by one of two types of surgery: left or right temporal resection, which removed the entire amygdala along with parts of the corresponding temporal lobe. Each clip was rated on a scale of 1 to 10 for how well it expressed each of the four emotions. A group of normal individuals rated the same clips. This graph charts the results for two types of music clips: fearful or happy.
For happy music, the responses of normal and amygdala-free people were the same. But for scary music, while normal individuals rated it higher for “scary” than any other emotion 86 percent of the time, patients who had undergone the left temporal resection only rated it highest for “scary” 38 percent of the time. Results for the other surgery were similar. Surgery patients also had significant difficulty recognizing peaceful music.
But perhaps the surgery impairs music recognition in general. To test this, the experimenters included several clips with errors — obvious flubs that sounded like the pianist had stopped and restarted playing. The patients were as good as normal individuals at detecting the errors.
Gosselin’s team argues that this research shows that the amygdala plays a crucial role in recognizing scary music. One possible explanation is that the music mimics sounds that people use to alert each other to danger.
So, were you able to identify which song was scary and which was happy? Let us know in the comments.
Gosselin, N., Peretz, I., Noulhiane, M., Hasboun, D., Beckett, C., Baulac., M., & Samson, S. (2005). Impaired recognition of scary music following unilateral temporal lobe excision. Brain, 128, 628-640.