Image used for representation only.
Fear is a powerful tool for survival. But sometimes it can be misguided.
That excitable dog living down the street? Not a potential predator, it turns out. The presentation your colleagues are waiting for? Probably nothing to fear.
In a study published Thursday, scientists said they have identified how the brain overcomes an instinctive fear, offering clues that could benefit people who struggle with fear-related disorders, including phobias, anxiety and post-traumatic stress disorder.
"We’ve uncovered the mechanism by which the brain - through experience - can understand which potential instinctive dangers are actually not a danger,” Sara Mederos, a neuroscientist at University College London’s Sainsbury Wellcome Center who led the peer-reviewed Science study, said in a phone interview.
The researchers in Britain exposed mice to repeated harmless scenarios that mimicked danger and observed how they eventually learned to set aside their fears - shedding light on how the mammalian brain learns to keep calm and carry on in the face of an unfounded threat.
Because mice and humans share analogous neural pathways, the study authors said, their findings could indicate to medical researchers where in the human brain to target treatments for fear-related disorders.
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The study
In the laboratory experiment, scientists investigated how about 100 mice responded to a repeated visual threat that proved harmless over time - in this case, an expanding overhead shadow that mimicked a predatory bird’s swoop.
Initially, the mice ran for a shelter when the ominous shadow appeared, as their classic instinctive fear response kicked in. But after 30 to 50 simulated swoops, the scientists observed something: The mice came to realize the threat was harmless and learned to suppress their instinct. The rodents continued to forage and explore as normal, despite the shadow.
By inserting silicon probes into the mice’s brains, the study’s authors were able to track the neural mechanisms that lit up as the mammals learned to suppress their fear.
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The science
The study newly identified where the brain stores memories to disregard instinctive fears: a previously underexplored areaknown as the ventrolateral geniculate nucleus (vLGN).
Although it was previously known that this area was involved in the unlearning process, it was not clear until now that this was where memories were stored, Mederos said, adding: "We did not know that there is a chance of plasticity and learning happening in these downstream areas.”
The brain area sits between the neocortex, which detects a threat, and the brain stem, which activates the body’s instinctive response. Until now, scientists studying learning and memory in mice placed the brunt of their focus elsewhere in the brain, specifically on the visual cortex, Mederos said. The study found that while the visual cortex was crucial for learning to suppress instinctive fears, it was the vLGN that was crucial for storing the memory.
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How could humans benefit from this?
By understanding the structures in the brain that are activated through the process of unlearning, Mederos said, the research could eventually prove beneficial to those who have struggled to overcome fear-related disorders.
Medical researchers could target the same circuits in human brains through therapeutic interventions such as drugs, deep brain stimulation or functional ultrasounds, she said, though she noted that future research is needed.
"Targeting brain areas like the ventrolateral geniculate nucleus could open up new avenues to treat these disorders,” she said. The study also pointed to how specific molecules, mediated by neurotransmitters, are released in this area of the brain and allow fears to be unlearned.
"Particular drugs targeted specifically to the ventrolateral geniculate nucleus could be pharmacological approaches that would help with treating anxiety or PTSD,” she said.
