Human screams target brain’s fear centre

From ABC News in Science, 17 July 2015:

Does the sound of a human scream make your hair stand on end? Now scientists say they can explain why.

They’ve found the sound of human screaming is acoustically designed to plug directly into your brain’s fear and alarm circuit.

A study, published today in Current Biology , shows the acoustic characteristic of ‘roughness’ in screams triggers a response in the amygdala, and the ‘rougher’ a scream, the greater the fear response.

Lead author Dr Luc Arnal began investigating screams after a colleague confessed that his newborn baby’s screams were “hijacking his brain”, which got Arnal wondering what made screams so efficient as an alarm signal.

He asked his colleagues to record themselves speaking a normal sentence and then screaming as loud as possible.

“I took my colleagues because I didn’t want to have professional screamers, I just wanted people to produce whatever they could produce to have an idea of the variety of sounds that you can find,” says Arnal, a post-doctoral fellow in neuroscience at the University of Geneva.

Acoustic analysis of the screams showed they occupy a part of the acoustic spectrum that corresponds to a characteristic known as ‘roughness’, with high frequency fluctuations in the 30 to 150 Hz range.

“An analogy is the stroboscope in vision — these flashing lights that flash super-fast — we could call screams like strobophones, the idea is that it flashes the auditory information very fast,” Arnal says.

The researchers then asked volunteers to rate how frightening the different screams were, and found that the more ‘roughness’ there was in a scream, the more the volunteers were scared by it.

They also looked at how the screams affected brain activity, so volunteers were scanned using a functional magnetic resonance imaging (fMRI) machine while listening to the screams.

“The interesting thing is that we found that the amygdala was selectively sensitive to roughness, so the more roughness there was in the signal, the more the amygdala responded.” Read more.

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