Scientists discover a new way to suppress fear

Many people feel an automatic jolt of fear when they sense a sudden movement overhead. While this reaction can be a lifesaver in certain situations, it can also cause unnecessary distress.

Scientists have studied these swift responses to identify how the brain tells us to duck for cover. A recent study focused on mice reveals new clues about the links between primal fear circuits and learned safety.

“Fast instinctive responses to environmental stimuli can be crucial for survival but are not always optimal,” wrote the researchers.

“Animals can adapt their behavior and suppress instinctive reactions, but the neural pathways mediating such ethologically relevant forms of learning remain unclear.”

Learning to suppress fear

Study co-author Sara Mederos is a neuroscientist at University College London’s Sainsbury Wellcome Center.

“We were interested in trying to describe the mechanisms from behavior to the molecular level that could drive this learning to suppress fear,” said Mederos.

The researchers analyzed activity in the ventrolateral geniculate nucleus (vLGN), a structure deep in the brain that processes visual messages for rapid defensive behavior.

The experts found that with repeated proof of safety, the mice began ignoring an overhead shadow that previously caused them to run for cover.

Changing the script of fear

The researchers used optogenetics, a method for activating or silencing precise sets of neurons with light, to see how the higher visual cortex and lower regions interact.

Once the animals recognized the threat was a false alarm, the visual cortex relinquished control.

Scientists suggest that such top-down signaling reveals how the mind can block out reflexes once it learns a threat is harmless. This might open doors for understanding problems like anxiety, which affects over 40 million adults in the United States.

The role of the visual cortex

Early phases of learning hinged on activity in the higher visual areas that interpret what the eyes see. Mice unable to engage these cortical zones kept fleeing from the looming stimulus and missed the memo that it was safe.

Once the mice registered the new information, further reliance on the visual cortex dropped. This shift spotlighted the vLGN as the area responsible for holding on to the updated response, ensuring that learned calm stayed in place.

Connections in deeper brain structures can adapt swiftly and recalibrate how sensory input is interpreted. This study identified a role for endocannabinoid signals that appeared to tune neuron-to-neuron communication in the vLGN.

Adjusting the strength of those synapses helped the mice replace hardwired panic with a calmer take on the overhead movement. Once that rewiring took hold, fear responses dropped even if the usual triggers were present.

Neural circuits and fear regulation

The findings represent a significant advancement in understanding how the brain suppresses fear. 

“This study provides valuable insights into the neural circuits involved in fear regulation,” noted Felicity Nelson, a science journalist reporting on the research.

Nelson emphasized that while the research offers promising avenues for developing treatments for anxiety disorders, translating these findings from mice to humans will require further investigation.

Practical solutions for human anxiety

Researchers believe that unlocking these subcortical changes in mice could inform interventions for conditions like post-traumatic stress disorder.

Estimates from the U.S. Department of Veterans Affairs suggest that about six percent of Americans will experience PTSD during their lifetimes.

Some forms of therapy already emphasize facing and reinterpreting triggers to reduce fear responses. Tapping into the specific circuits that drive these shifts might improve how well those interventions work and how fast patients see benefits.

Addressing fear-related disorders

Scientists plan to refine methods such as focused ultrasound to stimulate or tone down specific brain cells without surgery. They want to see if humans can similarly learn to block out panic responses when they see no real danger.

“If we can get the same effects, then this could become an idea that can potentially lead to pre-clinical work,” said Mederos.

Many hope this approach might open new avenues to address fear-related disorders in clinical settings.

The study is published in the journal Science.

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