Fear Odor Reaction
December 13, 2013

Memories Of Fearful Odors Activate Heightened Sense Of Smell

redOrbit Staff & Wire Reports - Your Universe Online

Neuroscientists at Rutgers University have discovered that fear reactions can occur in the olfactory system, even before the brain has had an opportunity to interpret and associate a particular odor with trouble. In a study published Thursday in the journal Science, John McGann, associate professor of behavioral and systems neuroscience at Rutgers and colleagues, report that neurons in the noses of laboratory animals reacted  strongly to threatening odors before the odor message was even sent to the brain.

"What is surprising is that we tend to think of learning as something that only happens deep in the brain after conscious awareness," McGann said. "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."

McGann and his team made their discovery by using light to observe activity in the brains of genetically engineered mice through a window in the mouse's skull. They found that the mice that received an electric shock simultaneously with a specific odor showed an enhanced response to the smell in the cells in the nose, before the message was delivered to the neurons in the brain.

The research indicates that fearful memories can influence the senses, findings that could help improve our understanding of conditions like Post Traumatic Stress Disorder (PTSD), 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.

"What this study does is gives us a new way of thinking about how this might happen."

The researchers also discovered a heightened sensitivity to odors in the mice traumatized by shock. When these mice smelled the odor associated with the electrical shocks, the amount of neurotransmitter – chemicals that carry communications between nerve cells – released from the olfactory nerve into the brain was as large as if the odor were four times stronger than it actually was. This created mice whose brains were hypersensitive to the fear-associated odors.

Until now, scientists did not believe that reward or punishment could influence how the sensory organs process information.

McGann says he plans to continue his research to determine whether the hypersensitivity to threatening odors can be reversed by using exposure therapy to teach the mice that the electrical shock is no longer associated with a specific odor. McGann said this could help develop a better understanding of fear learning that might someday lead to new therapeutic treatments for anxiety disorders in humans.