When we see danger, we react . Whether we choose to run, hide, or face the threat head-on, our “snapshot” decision is the result of a complex brain mechanism that integrates visual data and triggers an appropriate response. How does this happen? A new study published in the journal Nature explains this.
In the animal kingdom, vision is vital for survival. This important sense informs the brain about predators and other threats, and, in turn, the brain generates an appropriate reaction: courage or fear, fight or flight.
But how is this process carried out? How do animals – humans – integrate visual information with the appropriate brain circuits that control our emotional states and then our behavior and actions?
A team of scientists led by Andrew Huberman of the Stanford University School of Medicine in California (USA) has found that certain brain circuits are “responsible” for the decision to fight or flee in the face of danger.
Although the study was conducted in mice, the findings are equally relevant for humans. In fact, the results have important implications for understanding and managing post-traumatic stress disorder (PTSD), addiction, and phobias .
To examine the rodents’ response to a threat, the researchers simulated the approach of a bird of prey and used the neuronal marker c-Fos to track the activity of neurons in the mice. They found increased activity in neurons that clustered together in a structure called the ventral midline of the thalamus. Through brain mapping they were able to see what sensory information was entering and what information was leaving this area.
They found that the midline of the thalamus receives information from a wide range of brain areas that process internal states, such as fear, but sends information very selectively to only two main areas: the basolateral amygdala and the medial prefrontal cortex.
The amygdala processes fear, aggression, and other emotions, while the medial prefrontal cortex uses its executive function to modulate emotional responses (as well as anxiety).
‘Flip’ the courage switch
By looking at the trajectory in the brain, the researchers wondered whether the selective inhibition of certain neurons along these pathways produced specific fight or flight reactions. To find out, they stimulated only the activity of the xiphoid nucleus while confronting the rodents with the image of the bird of prey. This caused the mice to freeze in front of the predator.
After that, they stimulated the activity of the tract that goes from the nucleus reuniens to the medial prefrontal cortex. This caused a surprising reaction: the mice became aggressive, preparing to defend themselves. An answer of undeniable courage or courage.
“You could hear their tails slapping against the side of the camera. It’s the mouse equivalent of slapping and slapping your chest and saying, ‘OK, let’s fight!’ “explains Andrew Huberman, project leader.
A second experiment confirmed the results: by exclusively stimulating the reuniens nucleus for half a minute before putting the predator in front of them, it produced the same behavioral response: instead of hiding, the mice shook their tails and exposed themselves in unprotected areas, ready to fight.
Huberman says the findings are highly relevant to humans, given that human brains have a similar structure to the ventral midline of the thalamus.
It suggests that people living with phobias, anxiety, or PTSD could soon benefit from the findings, as reducing activity in this area or in adjacent neuronal groups can help these people overcome their fears.
“This opens the door to future work on how to change ourselves from paralysis and fear to being able to face challenges in a way that improves our lives,” says Huberman.
Reference: Lindsey D. Salay, Nao Ishiko & Andrew D. Huberman A midline thalamic circuit determines reactions to visual threat. Nature (2018) DOID: doi: 10.1038 / s41586-018-0078-2
