For many people, hearing a bloodcurdling scream even from afar is enough to make their minds go into overdrive out of fear, and according to a new study, this is because this frightful shriek is designed to penetrate directly to the fear circuit of the brain.

A team of researchers from the University of Geneva in Switzerland have discovered that the acoustics of a scream is capable activating a response in the part of the brain known as the amygdala. This specific fear reaction becomes stronger depending on the roughness of the shriek.

Dr. Luc Arnal, a neuroscience researcher at the university and the lead author of the study, explained that they first came up with the idea of studying the effects of screaming after one of their colleagues told them that the screams of his newborn baby were "hijacking his brain."

Arnal said this made him wonder about the efficiency of screams in triggering alarm signals in the brain.

For their experiment, Arnal asked his fellow researchers to record themselves while they speak normal sentences. They were then to make another recording of them screaming as loud as they can.

"I took my colleagues because I didn't want to have professional screamers," Arnal said.

"I just wanted people to produce whatever they could produce to have an idea of the variety of sounds that you can find."

By analyzing the acoustics of the recorded screams, the researchers found that sounds fall under a section of the acoustic spectrum that relates to an aspect known as roughness. These high frequency fluctuations range between 30 and 150 hertz.

Arnal compared this finding to the stroboscope that is often used for vision, in which screams act like flashes that give off auditory information in an instant.

The Geneva researchers then asked participants to rate the frightening effect of various screams, and they found that the higher the roughness of the scream was, the more the participants became frightened by it.

Arnal and his team also measured the amount of activity in the participants' brains while listening to the screams through magnetic resonance imaging (MRI).

The results of the brain scan showed that the amygdala was particularly sensitive to the screams, and the more rough the shrieks were, the more responses the researchers observed in the amygdala.

The researchers also discovered that several kinds of artificial alarm signals demonstrated high levels of roughness, but further studies are needed to fully explore the effects of roughness. They believe that the efficiency of alarms in triggering a response from the brain occurs more by accident and not by design.

"There's almost nothing in the literature that says that you should use these frequencies to make an alarm signal alarming," Arnal pointed out.

The University of Geneva study is published in the journal Current Biology.

Photo: Maks Karochkin | Flickr

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