Everyone knows someone — or maybe is that person — who shuts their eyes tight during the scary parts of a horror film and forces their friend to go first in the haunted house.
Others avoid scary movies and haunted houses altogether during Halloween. In a study published in August, a team at the University of Colorado Boulder studied how people’s brains respond to threats and fear.
The researchers found that a group of neurons, called the interpeduncular nucleus or IPN, plays a role in controlling how people respond and adapt to threats. IPN is a brain circuit located in the midbrain near the brain stem. The team discovered that this circuitry is highly activated the first time a person sees a potentially threatening situation, but as soon as individuals realize there is no threat anymore, the IPN shuts down.
“The first time that you see a very scary movie and there is a scene that you are not anticipating, your IPN is going to be very activated,” psychology and neuroscience professor Susanna Molas said. “But if you see this movie, you re-watch the movie over and over across the same week, your IPN is going to start learning that the scary scene is not as scary anymore, and the IPN will be less active across repeated exposures. It’s the same if you go to a haunted house.”
The more frightened a person is, the more the IPN should be engaged, Molas said. It’s also possible that people who love haunted houses and have a high tolerance for scary movies might have a less active IPN. There may also be a cognitive aspect of the person having more rationale when dealing with spooky situations.
“I think that there is an interplay between natural threat responses, but at the same time, more cognitive assessment,” Molas said. “So it’s possible that some people have a different balance of the natural threat response versus thinking whether this situation is actually creating a danger or a harm.”
For the study, the research team exposed mice to a projected shadow periodically over three days that mimics the approach of an aerial predator. The mice’s instinct was to run away. The team used advanced imaging techniques to measure the mice’s brain activity during the threat. Molas said she was surprised by how quickly the mice adapted their behavior and stopped running away from the shadow.
“I was struck to see that by three days, the animals already understood that the threat is not a danger anymore,” Molas said.
Disruptions in the IPN circuit could also play a role in mental health conditions, such as anxiety and post-traumatic stress disorder. About 19% of adults in the U.S. have an anxiety disorder, according to the National Alliance on Mental Illness. In a normal threat response, the IPN activity decreases once the brain identifies that there’s no real threat. With anxiety, the IPN remains active in anticipation of a negative effect happening in the future.
It’s important to understand the causes and some of the brain regions involved with anxiety so scientists can develop better, more specialized treatments for it, Molas said.
“Anxiety is a very prevalent disorder in our society and the neural circuits behind that are still not completely understood,” she said. “There’s been huge progress, but there are some brain areas that, like the IPN, have not been considered for many decades.”
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