The brain is particularly attracted, even disturbed, by sounds with repetitive fluctuations found in frequencies between 40 and 80 Hertz. This is the type of sound that signals danger and usually attracts our attention. A research group of the University of Geneva (UNIGE) and the University Hospital of Geneva (HUG) wanted to investigate the issue and made some interesting discoveries about our brain in relation to the auditory system.
Researchers have shown that different and specific areas of the brain are particularly stimulated when sounds with these frequencies are perceived and that not only the conventional sound processing circuit is activated but also some cortical and sub-cortical areas relegated to the processing of salience and aversion. This would explain why the brain enters a sort of state of alert when it hears these sounds that it interprets as “alarms.”
The researchers carried out experiments on 16 participants listening to sounds from zero to 250 Hertz to understand which were the frequencies that were most annoying or unbearable. The researchers then asked the participants at what point they perceived the sounds as distinct from each other or as a continuous and single sound, as explained by Luc Arnal, a researcher at the Department of Neuroscience at UNIGE and one of the authors of the study.
The researchers found that above 130 Hertz frequencies are perceived with a continuous sound. They also found that the sounds considered unbearable by the participants in the experiment were those between 40 and 80 Hertz, the same frequency used by human alarms and screams, especially those of children.
This is likely to have developed at an evolutionary level as these alarms use these repetitive frequencies to maximize the chances of being detected. When sounds tend to stress the amygdala, the hippocampus and the insula, areas related to aversion and pain.
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