Screaming triggers alarm bells in the brain

Screaming has not only inspired various Hollywood blockbusters but it also has a remarkable power of piercing through other sounds to provoke an urgent sense of danger, says a study.

"If you ask a person on the street what's special about screams, they'll say that they're loud or have a higher pitch," said study senior author David Poeppel from New York University.

"But there's lots of stuff that's loud and there's lots of stuff that's high-pitched, so you'd want a scream to be genuinely useful in a communicative context," Poeppel said.

To find out that special something about screams, Poeppel and his colleagues listened to a lot of screaming. The team looked for a quality in screams and screamed phrases that sets them apart from other loud or high-pitched noises.

They used a new method of sound analysis called the modulation power spectrum (MPS).

According to the MPS, screams exhibited a quality called roughness, which means their volume rises dramatically and quickly, lead author Luc Arnal, neuroscientist at the University of Geneva, was quoted as saying in a Live Science report.

Normal speech has a roughness that ranges between four and five hertz (Hz). But screams can modulate much faster, ranging from 30 to 150 Hz.

"We found that screams occupy a reserved chunk of the auditory spectrum, but we wanted to go through a whole bunch of sounds to verify that this area is unique to screams," Poeppel said in the journal Cell Press.

The researchers also monitored brain activity in study subjects as they listened to screams and other sounds. Screams triggered increased activity in the amygdala, the region of the brain that processes fear response.

When scientists manipulated non-threatening sounds to increase their roughness, the listeners' apprehensive responses increased and this results in with more activity in the amygdala.