Sniffing Out Danger: Memories of Fear Can Trigger Heightened Sense of Smell

It turns out that we may just be able to sniff out danger--sort of. Scientists have discovered that a reaction to fear in mice can occur at the sensory level, even before the brain has the opportunity to interpret that the odor could mean trouble. The findings show that the nervous system can become especially sensitive to threats and that even fearful memories can influence the senses.

"What is surprising is that we tend to think of learning as something that only happens deep in the brain after conscious awareness," said John McGann, one of the researchers, in a news release. "But now we see how the nervous system can become especially sensitive to threatening stimuli and that fear-learning can affect the signals passing from sensory organs to the brain."

In order to see how sense of smell relates to fear, the researchers used light to observe activity in the brains of genetically engineered mice through a window in their skulls. The scientists found that the mice that received an electric shock simultaneously with a specific odor showed an enhanced response to the smell in the cells of the nose even before the message was delivered to the neurons in the brain.

So what do these findings mean? They indicate that fearful memories can influence the senses. This could help researchers better understand conditions like Post Traumatic Stress Disorder, in which feelings of anxiety and fear exist even though an individual is no longer in danger.

"We know that anxiety disorders like PTSD can sometimes be triggered by smell, like the smell of diesel exhaust for a soldier," said McGann in a news release. "What this study does is gives us a new way of thinking about how this might happen."

The next step in the research is to determine whether hypersensitivity to threatening orders can actually be reversed using exposure therapy. This, in turn, could help scientists develop treatments for humans who are suffering from PTSD or other anxiety disorders.

The findings are published in the journal Science.