Why does our 'blood run cold' when we hear strange noises?

How is it that a noise can make us jump or instantly create the feeling of having a lump in our stomach? By analysing how mice brains react to a startling sound, a duo of researchers has been able to highlight the neural mechanism behind this phenomenon. They published their results at the Cold Spring Harbor Laboratory.

In the brain of a mouse

Researcher Bo Li and colleague Xian Zhang focused on a part of the brain called the amygdala. It is at this level that visual, auditory or other stimuli are positively or negatively associated with the experience we have with them. This process of lifelong learning appears to be damaged in people with anxiety disorders or depression, and understanding it better could lead to targeted treatments.

The duo of researchers first trained mice to associate a particular sound with punishment, and another with a reward. ‘Looking at the patterns of neural activity in the amygdala, you can tell if the animal is expecting a reward or fears punishment,’ says Li. It should be noted that the punishment took the form of a breath of air that made the mouse jump, while the reward was a drop of fresh water.

Anticipation or experience, is there a difference?

Thanks to implants placed in the animals’ brains, the researchers were able to observe the evolution of the animals’ reactions before, during and after training. At the beginning of the experiment, the neurons activated without any particular motive when the mice heard a sound. However, a particular pattern began to emerge when one of the sounds was associated with the breath of air.

This pattern resembled the one researchers observed when the mouse actually experienced punishment. Similarly, hearing the sound associated with the reward, the neurons of the mouse were activated as if it received a drop of fresh water. When a sound makes us jump or freezes our blood, it is probably that our neurons respond to it as if they were already experiencing the danger we have learned to associate with it in our lifetime.