When the irrelevant becomes critical

The emotional stimuli, especially the threatening ones (a spider, a pointing gun or a scream) provide humans with crucial information for survival. For that reason, our brain responds faster and more efficiently to those stimuli than to any other present stimulus in the environment.

That happens because our sensory systems are limited and, therefore, we cannot process all incoming information. We have to quickly distinguish what is important from what is not in order to rapidly react. In this sense, an archaic part of our brain, the limbic system, is in charge of deciding which stimuli can be dangerous and must be firstly processed, or even better processed, than the other stimuli. Most of the times, in fact, that happens in a few milliseconds, making us unaware of this process. And here lies the relevance of emotional processing.

But the brain should not limit itself to better process a certain emotional stimulus. Sure everyone remembers the last sequences of a famous Hollywood thriller from the 90s, The Silence of the Lambs, where Agent Clarice Starling enters into the serial killer’s house and fumbles through the darkness. As she emerges from the bathroom with both hands on the gun, in her raw-nerved blackness, every sound occurring in that moment is unnaturally magnified (the humming of the refrigerator, the trickle of water or even her own terrified breathing).


Similarly, when an individual is in a threatening situation, he or she should be able to react to any stimulus appearing in that moment, even insignificant, as any information could be decisive.

In this study, published in Cerebral Cortex, we demonstrated that visualising emotional faces, either with a fearful or an angry expression, magnifies the processing of novel environmental sounds occurring in that moment. In fact, the brain areas related to auditory novelty processing become more activated under a negative emotional context, probably mediated by the amygdala, a nuclear complex with a critical role in the limbic system.

Fig 1. The Silence of the lambs. Jonathan Demme. Jodie Foster, Anthony Hopkins, Scott Glenn, Ted Levine. 1991. Lauren Films, S.A. (Spain).

Fig 2. Domínguez-Borràs, J., Trautmann, S.A., Erhard, P., Fehr, T., Herrmann, M., & Escera, C. (2008). Emotional context enhances auditory novelty processing in superior temporal gyrus. Cerebral Cortex, in press, doi:10.1093/cercor/bhn188. (link)