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Although it is normal to feel fear or anxiety in certain situations, we can adjust our fear reactions depending on our knowledge or the circumstances. For example, being awakened by loud explosions and bright lights nearby can cause a fear response. But if you have ever experienced fireworks, your knowledge will probably prevent such reactions and allow you to watch without fear. On the other hand, if you find yourself in a war zone, your fear response could be greatly increased.
Although many areas of the brain have previously been involved in processing perceived danger and mediating fear reactions, the mechanisms controlling these reactions are still unclear. Such control is crucial because its alteration can lead to anxiety disorders such as phobias or post-traumatic stress disorder (PTSD), in which the brain circuits associated with fear and anxiety are thought to become overactive, resulting in a pathological increase in fear responses.
The new study from the research group of Professor Sonja Hofer of the Sainsbury Wellcome Center at University College London, took advantage of an established experimental paradigm in which mice escape to a shelter in response to an expanding dark shadow. This impending stimulus simulates a predator moving towards the animal from above.
The researchers found that vLGN could control escape behavior based on the animal’s knowledge gained from previous experience and its risk assessment in its current environment. When the mice did not expect a threat and felt safe, the activity of a subset of inhibitory neurons in vLGN was elevated, which in turn could inhibit threat responses. In contrast, when the mice expected danger, the activity of these neurons was low, making the animals more likely to escape and seek safety.
“We believe that vLGN can act as an inhibitory gate that defines a threshold of sensitivity to a potentially threatening stimulus based on the knowledge of the animal,” said Alex Fratzl, a doctoral student at the Hofer laboratory and first author of the article.
The next piece of the puzzle the researchers are focusing on is figuring out what other regions of the brain vLGN interacts with to gain this inhibitory control of defensive responses. They have already identified such a region of the brain, the superior colliculus in the midbrain.
“We found that vLGN specifically inhibits superior colliculus neurons that respond to visual threats and thus specifically blocks the pathway in the brain that mediates responses to such threats – something the animal sees that could pose a danger as an approaching predator, “said Sonja Hofer, professor at the Sainsbury Wellcome Center and corresponding author of the article.
While humans don’t have to worry much about predators, they also have instinctive fear reactions in certain situations. The hope, therefore, is that clinical scientists will one day be able to determine whether the corresponding brain circuits in humans have a similar function, with clinical implications for the treatment of PTSD and other anxiety-related disorders in the future. .
Reference:
Fratzl A, Koltchev AM, Vissers N, et al. Flexible inhibitory control of defensive behavior visually evoked by the ventral lateral geniculate nucleus. Neuron. 2021. doi: 10.1016 / j.neuron.2021.09.003
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