Are You Calm When Scared, or Do You Panic and Flee? A Brain Circuit Explains Why
Fear is a fundamental emotion embedded early in evolution to guarantee our survival. But besides the ability to experience fear, how we respond to it is just as important.
Now, a research team from the University of Colorado Boulder has discovered a new brain circuit that manages how we respond to threats, operating independently of the amygdala, the brain’s primal fear center. The interpeduncular nucleus (IPN) activates freeze-and-flee reactions when we face danger but also adjusts when a seemingly threatening situation turns out to be harmless.
“Our study shows how the brain learns to fine-tune those responses through experience, helping us adapt to the world,” said the study’s first author Elora Williams, a graduate student in the Department of Psychology and Neuroscience, in a news release.
Based on their findings, the team suggests that people with dysregulated fear responses, such as individuals with anxiety, post-traumatic stress disorder (PTSD), or even thrill-seekers, might behave that way because their IPNs are not functioning properly. Continued research could establish new pathways to address IPN dysregulation, leading to more balanced fear responses.
Read More: The Science of Recreational Fear: Why We Love Horror Movies and Other Spooky Thrills
Fear Response for Mice
For their study, published in Molecular Psychiatry, the team built a “mouse haunted house,” letting mice explore a maze while exposing them to a predator-like projection to trigger a fear response.
Using fiber photometry, a method that tracks neural activity in real-time, the scientists could see how the mouse brain processes fear in remarkable detail. On the first day, the predator projection triggered the expected reaction, with mice freezing on sight and dashing to safety, corresponding with their IPNs showing high activity. On the second day, the mice began to adjust to the looming predator, showing more curiosity about their surroundings, which is a sign of reduced fear.
By the third day, the mice seemed unbothered by the predator stimulus, having learned it wasn’t dangerous. As expected, their IPN activity dropped accordingly.
Operating the Fear Circuit Manually
Next, the researchers wanted to confirm their observations by directly manipulating the IPN circuit within the mice’s brains. Using optogenetics, a technique that genetically modifies neurons to respond to light, they were able to control the rodents’ fear responses like flipping a switch in their brains.
Regardless of whether the animals were seeing the predator for the first time or the third, their fear responses depended entirely on whether the scientists had activated or silenced the IPN neurons.
“Collectively, these findings implicate the IPN as a critical circuit for helping us process potential threats and adapt accordingly when we learn they aren’t putting us in danger,” said senior author Susanna Molas, assistant professor in the Department of Psychology and Neuroscience, in the news release.
Risk Takers and People With Anxiety
This is the first study to assign such an important role in regulating fear to the IPN, an underexplored brain area compared to the amygdala and hippocampus, the brain’s established fear-processing centers.
“Identifying the neuronal circuits underlying threat processing and adaptive learning is vital to understanding the neuropathology of anxiety and other stress-related conditions,” added Williams.
The research team hopes that future studies will explore this circuit further to better understand what role the IPN plays in both risk-takers and people with anxiety, two groups that seem to respond to fear in unusual ways.
“The brain’s threat system is like an alarm. It needs to sound when danger is real, but it needs to shut off when it’s not,” said Williams, who hopes potential treatment options will eventually target the IPN.
Read More: How the Brain Recognizes and Rationalizes Fear
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