Why is it that a high-pitched scream causes us to drop everything and give 100% of our attention to the source of the noise?

It’s not just because screams are loud. Lots of other things in our daily lives are loud. But high decibel screams in particular are impossible to ignore. 

Here’s why: Human screams contain fast, barely perceptible fluctuations in loudness, usually at frequencies of between 40 and 80 Hz. This frequency makes them acoustically shocking to our ears. And now, thanks to new studies, we understand why human screams hijack our brains into paying attention. 

A research team at the University of Geneva has found that the 40 to 80 Hz frequency range triggers reaction in brain areas related to more than hearing – this frequency also triggers the brain’s aversion to pain. 

The new study, published in Nature Communications, invited16 participants to listen to streams of repetitive clicks played at various frequencies, between 50 to 250 Hz. At frequencies below about 130 Hz, participants could hear distinct clicks. Above this frequency, the clicks were usually perceived as being one continuous sound. 

The participants reacted particularly vehemently to very loud, unpleasant sounds, with fluctuations in the range of 40-to-80 Hz. This is the same range of frequencies heard in home alarm systems, sirens, and human screams, including a baby’s scream of intense distress.

Researchers attached a type of EEG directly to study participants’ brains so they could see what areas of the brain were aroused when these particular screams were heard. They found that when an intense 40-to-80 Hz scream was experienced, it was perceived as excruciating and affected highly specialized areas of the brain. 

In fact, the EEG showed synchronized patterns of activity in a number of brain areas, including the amygdala, hippocampus and insula. These areas are all related to the experience of pain, which explains why participants perceived these intense sounds as being unbearable. The amygdala, hippocampus and insula areas if the brain experiences these intense sounds as high danger, activating cortisol release – the “fight or flee” hormone — so that the sounds are impossible to ignore. 

Listening to our environment, we hear how we have learned to exploit the brain’s recognition of danger calls by engineering car alarms, home alarms, tornado sirens, and fire engines with the same danger frequency range to get their urgent messages across. 

At INDY Neurofeedback, we find our complex brains endlessly fascinating. If you have a question regarding the way your brain works, let’s talk. Our goal is for your brain to work optimally.