Brain Circuits for Fear Responses

Brain circuits or brain mechanisms that regulate threat/fear responses in animals have been discovered.

Brain circuits or brain mechanisms that regulate threat/fear responses in animals have been discovered by a study “Flexible inhibitory control of visually-evoked defensive behaviour by the ventral lateral geniculate nucleus”, at the Sainsbury Wellcome Centre, published in Neuron.

This enables the mice to override their instincts based on previous experience. It is normal for a person to experience fear or anxiety in certain situations. However, it can be adjusted based on our previous knowledge or circumstances.

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‘Brain circuits or brain mechanisms that regulate threat/fear responses in animals have been discovered.’

Many brain regions are known to be involved in mediating fear reactions. In addition, the control of these reactions is crucial as its impairment may lead to anxiety disorders such as phobias or post-traumatic stress disorders (PTSD).

However, the precise mechanisms of controlling these reactions are still unclear. The study team thereby established an experimental paradigm using a mice model where it tries to escape to a shelter in response to an overhead expanding dark shadow.

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It was found that suppressed activity in a new brain circuit in the ventral lateral geniculate nucleus (vLGN – an inhibitory brain structure) allowed the animals to seek safety and escape from perceived danger.

On the contrary, the activation of vLGN neurons completely abolished escape responses to imminent threats. The vLGN was found to control the escape behavior of the animal, depending on its previous knowledge and experience.

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“We think the vLGN may be acting as an inhibitory gate that sets a threshold for the sensitivity to a potentially threatening stimulus depending on the animal’s knowledge,” says Alex Fratzl, a Ph.D. student in the Hofer lab and first author of the paper.

“We found that the vLGN specifically inhibits neurons in the superior colliculus that respond to visual threats and thereby specifically blocks the pathway in the brain that mediates reactions to such threats – something the animal sees that could pose a danger like an approaching predator,” says Sonja Hofer, Professor at the Sainsbury Wellcome Centre and corresponding author on the paper.

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The study findings thereby may help ascertain if these brain circuits hold clinical implications for the treatment of PTSD and other anxiety-related disorders in the future.

Source-Medindia