When most people hear a bloodcurdling scream even from a distance, this is enough to to make them feel immediate fear where a frightening shriek apparently triggers the fear circuitry of the human brain, according to a new study.
Researchers from the University of Geneva in Switzerland have determined that a scream's acoustics can actually activate an emergency response from the brain in the part known as the amygdala. This fear induced reaction also grows and becomes more powerful depending on how the scream is loud or rough enough to the ears.
According to lead author of the study, Luc Arnal, who is a neuroscience researcher from the University of Geneva, the team first conceived of this idea to study further the effects of a human scream when one of their members expressed to them that newborn infant screams are "hijacking his brain".
Arnal was then curious of how a scream can efficiently trigger something so alarming in the brain, sending these emergency signals.
During the experiments, Arnal and his team members recorded themselves while speaking in regular sentences. Another recording was made that involves them screaming as loud as they possibly can. Arnal adds that, he has chosen his colleagues since he does not want any professional screamers so that people can just produce loud shrieks in order to find different variety of sounds within those screams.
When researchers have analyzed the acoustics of the recorded screams, they discovered that the sounds were classified under an acoustic spectrum that is related to a quality called roughness. The high frequencies of the screams fluctuated from 30 to 150 hertz.
Participants of the study were then asked to rate the fright factor of the various screams where the researchers revealed that the higher the roughness of the scream, the more frightening it was.
Researchers also obtained measurements from their brain activity while participants listen to these screams via MRI (Magnetic Resonance Imaging). Results revealed that brain scans presented the amygdala being especially sensitive to screams and when screams are rougher, it was observed that there were more responses from the amygdala.
This new study is published in the journal Current Biology.