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 Researchers who explored how the brain handles a scream said on
Thursday the loud, high-pitched sound targets a deep brain structure
called the amygdala that plays a major role in danger processing and
fear learning.
"We knew pretty well what frequencies are used by speech signals and
the brain regions involved in speech processing: the auditory cortex
and higher order regions such as Broca's area, for instance," said
University of Geneva neuroscientist Luc Arnal, whose research
appears in the journal Current Biology.
"But what makes screams so special and unpleasant and how the brain
processes these sounds was not clear," Arnal said.
The researchers said an acoustic quality called "roughness," the
quick change in sound loudness, sets screams apart from other
sounds.
 "Normal speech patterns only have slight differences in loudness,
between 4 and 5 Hertz (sound wave cycles per second), but screams
can modulate very fast, varying between 30 and 150 Hertz," Arnal
said, explaining the "roughness" of screams.
As part of the study, the researchers played recordings of screams
from horror movies, YouTube videos and those made by volunteer
screamers in a laboratory, and asked people to judge how frightening
these were. Those with the highest "roughness" were found to be the
most terrifying.
To learn how these sounds were processed, the researchers monitored
brain activity using a neuroimaging method called functional
magnetic resonance while the study's subjects listened to screams.
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They found that the screams increased the activation of the fear
response in the amygdala, an almond-shaped structure situated deep
inside the brain's medial temporal lobe.
"In terms of potential applications, our findings could be used to
improve the way we design alarm sounds. The same way a bad smell is
added to natural gas to make it easily detectable, adding roughness
to alarm sounds may improve and accelerate their processing," Arnal
said.
Arnal said he is planning future research on infant screams to see
if those have extra roughness.
"I started being interested in screams when a friend of mine told me
that the sound of his newborn's screams was literally hijacking his
brain, and I wondered what makes screams so efficient as an alarm
signal," Arnal said.
(Editing by Eric Walsh)
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