The smell of death triggers fight-or-flight response in humans

Just like with other types of animals, the smell of death triggers an unconscious fight-or-flight response in humans, researchers from the University of Kent School of Psychology and the Arkansas Tech University Department of Behavioral Sciences have discovered.

In four different experiments, Dr. Arnaud Wisman from the Canterbury, UK school and his US-based colleague Ilan Shrira exposed people both consciously and unconsciously to putrescine, a foul-smelling chemical compound partially responsible for the stink of decomposing flesh.

As reported in the journal Frontiers in Psychology, exposure to the chemicals was found to initiate a person’s instinctive threat-management responses, and that even short-term exposure to putrescine increased awareness, resulting in a readiness to either escape or defense oneself.

Their research is the first to demonstrate that an odor emanating from a specific type of chemical compound (in this case, putrescine) could be perceived as threatening, the study authors said in a statement. All previous chemosignal evidence had been transmitted through perspiration.

In addition, Dr. Wisman and Shrira believe their paper is one of the first to demonstrate that a specific chemical compound could directly lead to overt behavioral changes in humans. Their findings could help determine specifically which brain and sensory pathways are involved in the detection and processing of chemosensory threats.

Smell of death is a warning sign of perceived threats

In the first of four experiments used to test putrescine’s impact on threat management systems in humans, the researchers found that it increased vigilance, as measured by a reaction time task. In the second, they discovered that exposure to the chemical compound caused people to exit out of the exposure site more quickly than exposure to ammonia or an odorless control scent.

The third experiment found that putrescine caused implicit cognitions associated to a threat and to escape mechanisms, while the final one showed that exposure to trace amounts of putrescine (less than could be consciously detected) increased hostility towards third parties. The results are the first to demonstrate that people can process the smell of death as a warning sign that serves as a catalyst to protective responses to perceived threats.

These findings suggest that the smell of putrescine activates a neurological pathway similar to the one used to prepare fight-or-flight responses to perceived threats. That pathway involves the central nucleus of the amygdala, the midbrain periaqueductal gray, the hypothalamus, and the brainstem, which combine to trigger a physiological reaction.

Additional research on the topic, they said, could include measurements of blood pressure, heart rate, and other physiological functions to test the observed effects of putrescine on subjects. Also, the authors noted that future studies could attempt to understand the precise nature of the threat produced by the chemical compound – whether it is microbial, predatory, or something else.


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