Brain pathway discovered that suppresses fear

Fear shapes human behavior in profound ways, influencing our reactions and survival responses. While some fears are innate, others can be unlearned through experience, a process that has long intrigued neuroscientists.

Now, researchers have identified a crucial brain pathway that helps suppress fear, and sheds new light on how we adapt to perceived threats.

The findings could pave the way for innovative treatments for fear-related disorders such as phobias, anxiety, and post-traumatic stress disorder (PTSD).

The study, conducted by scientists at the Sainsbury Wellcome Centre (SWC) at UCL, unravels the neural mechanisms behind fear suppression, and offers a fresh perspective on the role of learning, memory, and emotional regulation.

The brain helps us unlearn fear

Led by Dr. Sara Mederos and Professor Sonja Hofer, the research team investigated how we unlearn fear.

“Humans are born with instinctive fear reactions, such as responses to loud noises or fast-approaching objects,” said Dr. Mederos.

“However, we can override these instinctive responses through experience – like children learning to enjoy fireworks rather than fear their loud bangs. We wanted to understand the brain mechanisms that underlie such forms of learning.”

The researchers employed a novel experimental approach using mice. They observed that when presented with a perceived threat – an overhead expanding shadow that mimicked an aerial predator – the mice initially sought shelter.

Over time, however, they learned to remain calm, giving the researchers a model for studying how we suppress our fear responses.

Decoding the brain’s fear pathway

Expanding on their previous findings, the team studied the ventrolateral geniculate nucleus (vLGN), a brain region that can suppress fear responses when active. They also explored its role in tracking past experiences of threats.

Two significant findings emerged. First, particular regions of the visual cortex were essential for learning. Second, the vLGN stored the memories that were formed during this learning process.

“We found that animals failed to learn to suppress their fear responses when specific cortical visual areas were inactivated. However, once the animals had already learned to stop escaping, the cerebral cortex was no longer necessary,” explained Dr. Mederos.

New perspective on learning and memory

These discoveries challenge conventional beliefs about learning and memory.

“While the cerebral cortex has long been considered the brain’s primary center for learning, memory and behavioral flexibility, we found the subcortical vLGN, and not the visual cortex, actually stores these crucial memories,” said Professor Hofer.

“This neural pathway can provide a link between cognitive neocortical processes and ‘hard-wired’ brainstem-mediated behaviors, enabling animals to adapt instinctive behaviors.”

The team also revealed the cellular and molecular mechanisms behind this process. Learning occurs through increased neural activity in certain vLGN neurons, and is prompted by the release of endocannabinoids, which are known to regulate mood and memory.

This leads to heightened activity in this brain area when encountering a visual threat, thereby suppressing fear responses.

Implications and future directions

The value of these findings could reach far beyond the laboratory.

“Our findings could also help advance our understanding of what is going wrong in the brain when fear response regulation is impaired in conditions such as phobias, anxiety and PTSD,” said Professor Hofer.

“While instinctive fear reactions to predators may be less relevant for modern humans, the brain pathway we discovered exists in humans too.”

Next, the team will collaborate with clinical researchers to further explore these brain circuits in humans. The goal is to create new, targeted treatments for maladaptive fear responses and anxiety disorders.

Bridging research and treatment

The discovery of this fear-regulating brain pathway could have profound implications for mental health treatment.

By understanding how the brain suppresses instinctive fear responses, researchers may be able to develop new therapies for individuals struggling with fear-based disorders.

Traditional treatments, such as exposure therapy and cognitive behavioral therapy, rely on retraining the brain to respond differently to fear-inducing stimuli.

However, targeting the vLGN directly could offer a more precise approach that leads to faster and more effective treatments.

As scientists continue to map the brain’s intricate fear circuitry, the hope is that these insights will translate into breakthroughs in mental health care, offering relief to millions affected by excessive or maladaptive fear responses.

The full study was published in the journal Science.

Image Credit: Sainsbury Wellcome Centre

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