Although it is normal to experience fear or anxiety in some situations in life, the truth is that we can adjust our responses based on our context. For example, if you wake up with loud explosions and bright lights and it is the festivities of your town, you know that it is fireworks and you will be able to watch them or continue to sleep without fear. But if you live in a war zone, these kinds of stimuli will probably scare you.
It was previously known that many brain regions are involved in the processing of perceived danger and in the mediation of fear reactions, but the mechanisms that control these functions are unclear. Such control is crucial as its deterioration can lead to anxiety disorders such as phobias or post-traumatic stress disorder (PTSD), in which brain circuits associated with fear and anxiety are believed to become hyperactive, leading to pathological increase in responses to fear.
In a study published in the journal Neuron , a team of scientists took advantage of an established experimental paradigm in which mice escape to a shelter in response to an expanding dark shadow. This looming stimulus simulates a predator moving towards the animal from above.
The researchers found that the ventral lateral geniculate nucleus (vLGN), an inhibitory structure in the brain, could control escape behavior depending on the knowledge of the animal gained through previous experience and its assessment of risk in its current environment. When mice were not expecting a threat and felt safe, the activity of a subset of inhibitory neurons in vLGN was high, which in turn could inhibit threat reactions. In contrast, when the mice expected danger, the activity in these neurons was low, making the animals more likely to escape and seek safety.
“We believe that vLGN may be acting as an inhibitory gate that sets a threshold for sensitivity to a potentially threatening stimulus depending on the knowledge of the animal,” said Alex Fratzl, a doctoral student at University College London and first author of the paper.
The next piece of the puzzle the researchers are focusing on is determining what other brain regions vLGN interacts with to achieve this inhibitory control of defensive reactions. They have already identified one such brain region, the superior colliculus in the midbrain.
“We found that vLGN specifically inhibits neurons in the superior colliculus that respond to visual threats and thus specifically blocks the pathway in the brain that mediates reactions to such threats, something the animal sees as potentially posing a danger. like an approaching predator, “explains Sonja Hofer, another author.
While humans don’t have to worry much about predators, they also have instinctive fear reactions in certain situations. Therefore, the hope is that clinical scientists may one day determine whether corresponding brain circuits in humans have a similar function, with clinical implications for treating PTSD and other anxiety-related disorders in the future.
