How the brain regulates fear: a new clue discovered in mice

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Fear. This visceral emotion that freezes our blood, makes our hearts beat wildly and prepares us to flee or fight. But how does our brain manage not to remain a prisoner of this primitive reaction ? This is the question to which a team of researchers has just provided the beginning of an answer, by identifying in mice a real “neuronal brake” on fear. The results of their research were published on August 5 in the biology journal Cell Reports.

The amygdala, the unexpected policeman of our emotions

At the heart of this discovery lies the amygdala, a brain structure long considered the seat of our fears. But now it is revealing a new facet of its personality. Dr. Wen-Hsien Hou and colleagues at Yang Ming Chiao Tung University (NYCU) have discovered a group of nerve cells that are playing spoilsport in the great dance of fear.

Imagine laboratory mice, conditioned to associate a sound with an unpleasant electric shock. When our rodents hear this fateful sound again, a specific group of neurons awakens in their amygdala. However, against all expectations, these cells are not there to sound the alarm.

Quite the opposite! “When these specific nerve cells were inhibited, the mice remained frozen longer in anticipation of an electric shock,” says Dr. Hou. In other words, without these peacemaking neurons, our little whiskered friends would be trembling in fear for much longer than necessary.

GABA vs. Glutamate: The Duel of the Neurotransmitters

What makes this discovery particularly intriguing is the very nature of this neural circuit. While most memory circuits operate on glutamate, an excitatory neurotransmitter that typically stimulates neuron activity, our “fear brake” prefers GABA (gamma-aminobutyric acid), a neurotransmitter with a more calming effect.

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Dr. Cheng-Chang Lien, a neurophysiologist at NYCU, sums it up this way: “These cells act as brakes, preventing excessive fear responses.” We could compare them to a wise bartender who, seeing a customer who is too agitated, would decide to cut his coffee with a little water in order to calm his ardor.

From Mouse to Human: A Giant Leap for Science

Of course, there is more than just a change in scale between the brain of a mouse and that of a human. Our similarities are numerous, but our differences are just as numerous. There is still a long way to go before we can say that we too possess this fear regulation mechanism.

However, this discovery brings a breath of hope to the world of research on anxiety disorders and post-traumatic stress (PTSD). If an equivalent circuit were identified in humans, it could well revolutionize our understanding and approach to these disorders. Imagine being able to one day “adjust” this neural brake in people suffering from chronic anxiety or who are constantly reliving trauma. This would be a phenomenal step forward from a therapeutic point of view.

Identifying this “fear brake” in mice is only a first step. But what a step! It reminds us that our brain, far from being a simple fear machine, has sophisticated mechanisms for regulating our emotions. A true lesson in humility in the face of the complexity of this organ that will perhaps never cease to surprise us. While research continues relentlessly in the field of neuroscience, one thing is certain: we have not finished exploring the dark corners of our brain.

• Researchers have identified a group of neurons in the amygdala of mice that acts as a “fear brake.”
• Unlike typical memory circuits, this mechanism uses the neurotransmitter GABA.
• The discovery could open new avenues for treating anxiety disorders and post-traumatic stress in humans.

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