Your brain makes life-or-death decisions in milliseconds, and scientists just figured out exactly how it chooses between fight, flight, or freeze. New research reveals that two competing neural highways determine whether you’ll face danger head-on or hide under the covers. Understanding this wiring could finally explain why anxiety affects everyone differently.
Scientists at the University of Florida have also figured out how our brains decide whether a smell is pleasant or revolting. The same neural pathways that control fear also determine whether you love the aroma of fresh coffee or can’t stand the lingering scent of microwaved fish.
“Odors are powerful at driving emotions, and it’s long been thought that the sense of smell is just as powerful, if not more powerful, at driving an emotional response as a picture, a song or any other sensory stimulus,” says senior author Dan Wesson from the UF College of Medicine, in a statement.
The Brain’s Fear and Smell Network
The research, published in Molecular Psychiatry, focused on a brain region called the basolateral amygdala. This is the brain’s alarm system that decides whether something is dangerous or pleasant. This area connects to the ventral striatum, a region involved in motivation and movement.
“This is, in part, what we mean when we say your sense of smell is your most emotional sense,” says first author Sarah Sniffen from the UF College of Medicine. “Yes, smells evoke strong, emotional memories, but the brain’s smell centers are more closely connected with emotional centers like the amygdala.”
Using genetically modified mice, the researchers identified two distinct types of brain cells based on the genes they express, Drd1+ and Drd2+ neurons. They each carry specific information to different destinations.
Scientists tracked exactly where these neural pathways go and what happens when they’re activated or shut down. They injected special viruses that made specific brain cells glow under certain lights, allowing them to trace the complete circuit maps.
The study revealed that these two types of brain cells create parallel highways that lead to different neighborhoods in the ventral striatum. The first pathway (Drd1+ neurons) primarily connects to an area called the nucleus accumbens, while the second (Drd2+ neurons) mainly links to a region called the tubular striatum.
Initially, the team expected that one cell type would generate positive emotions while another would generate negative emotions. Instead, they discovered something more complex and potentially more powerful for future treatments.
“It can make an odor positive or negative to you,” says Wesson. “And it all depends upon where that cell type projects in your brain and how it engages with structures in your brain.”
When researchers artificially activated these pathways, they discovered the circuits had specific effects on behavior. Mice avoided areas where the Drd1+ pathway to the nucleus accumbens was stimulated, as well as areas where the Drd2+ pathway to the tubular striatum was activated, but in different ways.
Fear Learning and Smell Associations
The researchers then tested how these pathways affect learning to associate smells with danger, similar to how you might learn to fear the smell of smoke after experiencing a fire.
Monitoring the animals’ breathing patterns and movement, the team paired neutral odors with mild foot shocks. They then chemically silenced specific pathways during this learning process to see which circuits were necessary for forming fear memories.
Blocking the Drd1+ pathway to the nucleus accumbens significantly reduced fear learning, as did blocking the Drd2+ pathway to the tubular striatum. However, the other pathway combinations didn’t affect learning, showing that the destination matters as much as the origin.
Human Anxiety and Sensory Issues
This research was conducted in mice, but the brain structures involved are similar in humans.
“We’re constantly breathing in and out, and that means that we’re constantly receiving olfactory input,” says Sniffen. “For some people, that’s fine, and it doesn’t impact their day-to-day life. They might even think, ‘Oh, odors don’t matter that much.’ But for people who have a heightened response to sensory stimuli, like those with PTSD or anxiety or autism, it’s a really important factor for their day-to-day life.”
Modern anxiety medications largely work by broadly dampening brain activity throughout the brain. But this research suggests a more surgical approach might be possible, targeting specific pathways based on an individual’s particular symptom pattern.
This research could help clinicians address specific problems, like helping a patient who associates a clinic’s smell with transfusions that made them queasy, or restoring appetite in people who’ve grown indifferent to food due to illness.
Medications could potentially suppress some pathways’ activity to help people overcome stressful responses, or activate them to restore enjoyment to things people have lost interest in.
“Emotions in part dictate our quality of life, and we’re learning more about how they arise in our brain,” says Wesson. “Understanding more about how our surroundings can impact our feelings can help us become happier, healthier humans.”
Rather than treating all anxiety as the same disorder, we now have evidence that different fear responses run on different tracks. That means we can potentially start building treatments that actually match the problem.
Source : https://studyfinds.org/brain-links-smells-to-fear-anxiety/
