Researchers from the University of Geneva have found that witnessing negative behaviors triggers similar neural responses as smelling unpleasant odors, as opposed to feeling pain.
Until now, two conflicting theories have existed on peoples' neural responses to bad behavior. Some say that neural pathways linked to disgust are activated when witnessing it- just as feeling disgust when smelling rotten foodstuffs (thus avoiding the food) prevents poisoning. Others, however, say that neural pathways linked to pain come into play, as pain from injuries helps activate our withdrawal reflexes.
To reveal which of the two theories matches reality, the researchers conducted an experiment to compare the two inputs. To do so, they subjected volunteers to either unpleasant smells or heat-induced pain. They did this to establish a baseline from which to measure how they influence neural activity. Once the inputs had been calibrated, the participants were asked to read passages that evoked value judgments.
In particular, they read the train dilemma, in which five people are stuck on a railway track as a train approaches, and the only way to save them is to push someone off the top of a bridge. Essentially, they had to choose between saving one life or five.
In the end, the researchers found that while reading the passage influenced how the participants smelled certain odors, their perception of pain was not influenced, as measured by testing the electrical conductance of their skin.
Next, the researchers set to decipher the neural activity behind their smells. Using an MRI technique that measured their global neuronal activity rather than that of specific regions, the researchers found that the participants' previous moral judgment from the text influenced their overall brain activity to correspond with disgust rather than pain.
In doing so, the researchers also uncovered a biomarker for disgust for the first time, making their discovery a 'double step forward', according to the study's lead investigator, Professor Corrado Corradi-Dell'Acqua.