You emerge from your sleep and head to the bathroom. The light goes on. A large spider enters your field of vision. If you were in a lab experiment, scientists would have noticed intense electrical activity in a region of your brain called the periaqueductal gray (PAG). This pattern is also seen in other animalsThe logical conclusion? The PAG controls the fight-or-flight response in mammals to threatening situations.
Yet it is a received idea. The brain does not have neural circuits dedicated to the choice between flight and fight. Recent studies, including that of Lisa Feldman Barrett, professor at Northeastern University in Boston (United States), demonstrate that our relationship with life is not based solely on the detection and reaction to threats. In fact, the brain is more concerned with prevention than reaction. Its first mission: to reduce uncertainty in a constantly changing world.
This snapshot of the neural circuits involved in the fight-or-flight response is called the “triune brain theory” and dates back to PlatoThe Greek philosopher explained that the human brain had evolved to form three layers. The first would come to us from reptiles and would control instinctive needs, the second would be borrowed from ancient mammals and would take care of emotions, and the third, a human specificity, would rationally limit our inner beast.
Now, Plato lived two millennia before Darwin, and it shows. Already, reptiles are not the ancestors of mammals. Above all, human brains are similarly formed to those of animals. Scientists have discovered, thanks to advances in molecular genetics, that mammals have the same types of neurons as humans, including in the “rationality layer.” To top it all off, it has long been known that there is no system exclusively dedicated to emotions. Nor to reason.
The brain plans by learning
So what’s left of our fight-or-flight response story? Three types of research scientists bring us real answers. The first comes from ever more advanced brain imaging. Lisa Feldman Barrett’s lab recently proved that the PAG experiences a spike in activity, even in completely non-stressful and completely mundane moments. Anatomical study shows that this PAG coordinates the activities of the heart and lungs with other brain systems. It is not activated only in the face of threats, but all the time. It simply works harder under stress.
The second scientific proof is found in the study of mice. When exposed to a threat such as an unknown object or the smell of a predatora mouse does not have a binary fight-or-flight response. More often, it retreats before cautiously returning, and repeats this back-and-forth over and over again. Human children behave similarly when faced with animals or waves on the beach. In fact, it is a careful gathering of information to reduce the uncertainty of the immediate environment.
Finally, a third scientific answer comes from the last twenty years of research on the brain’s predictive ability. In everyday life, you jump when you see a car coming towards you. You smile when you receive a text from a loved one. In more scientific terms, you are responding to a stimulus. Except that your brain is not reacting, it is predicting in advance how to act and what sensations to feel in the immediate future. All thanks to all its past experiences. It is called “learning”.
Reducing uncertainty is not neutral in energy spent. The more the brain has to sustain or reinforce its effort (for example in the event of political, economic, climatic or personal instability), the greater the metabolic burden can be. This is stress. But it is worth it: we always consume less energy than if we had to face uncertainty. Reducing it improves, from an evolutionary point of view, the chances of survival, good health and reproduction.
These scientific explanations are perhaps less sexy. They do not give in to the intense tug-of-war between reason and emotion that would transform humans into Buridan’s donkey. Nor to myth of the three layers of the brain, including a reptilian one, which would manage the fight-responseleak. They simply illustrate that the brain anticipates the need to expend energy and prepares itself accordingly. And that is already almost a superpower.
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