Neuroscientists Unveil Key Brain Mechanism to Overcome Fear in Mice

Scientists at the Sainsbury Wellcome Centre (SWC) at University College London have identified a neural mechanism in mice that allows them to overcome instinctive fears. The study, led by Dr. Sara Mederos and Professor Sonja Hofer, reveals the precise brain regions responsible for suppressing fear responses.

Mice Learn to Suppress Fear Responses Over Time

In the experiment, naive mice instinctively sought shelter when exposed to a looming visual threat, such as an expanding shadow simulating a predatory bird. The threat was represented by three consecutive expanding black spots over three seconds, a well-established method for inducing fear and escape behavior. However, with repeated exposure, the mice learned that the stimulus was harmless and ceased to flee.

Understanding the Brain Mechanisms of Fear Suppression

“Just like children can learn to enjoy fireworks instead of fearing their noise, we can override instinctive responses through experience. We aimed to understand the brain mechanisms behind this form of learning,” explained Dr. Mederos.

Humans are also born with本能ive fear reactions, such as responding to loud noises or approaching objects. The study identified two key components in the learning process: specific visual cortex regions essential for initial learning and the ventral lateral geniculate nucleus (vLGN), which stores memories from this learning.

Role of vLGN and Endocannabinoids in Fear Suppression

The researchers found that increased neural activity in specific vLGN neurons suppresses fear responses. This process is enhanced by the release of endocannabinoids, which are internal messenger molecules in the brain known for regulating mood and memory. Endocannabinoids decrease inhibitory input to vLGN neurons, leading to greater activity in this brain area during the presence of the visual threat stimulus.

Implications for Treating Anxiety Disorders

This discovery could pave the way for therapies targeting the vLGN circuits or localized endocannabinoid systems to manage maladaptive fear responses and anxiety disorders such as phobias, anxiety, and post-traumatic stress disorder (PTSD). These conditions affect more than 300 million people worldwide.

Similarities in Human and Mouse Brains

While the study focused on mice, the same brain pathway exists in humans. The research team intends to collaborate with clinical researchers to investigate these brain circuits in humans, with the goal of developing novel and targeted treatments for anxiety disorders.

Professor Sonja Hofer emphasized, “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.”