Immobility due to stress: Riviera researchers explore the mechanisms of “freezing”

Paralyzed, speechless, unable to perform the slightest movement. Everyone who has been under intense stress has experienced that “feet stuck to the ground” feeling. She even has a name.

“Le freezing (“immobility” in French, Editor’s note) is a universal response to fear characterized by a complete lack of movement other than breathing.introduces Jacques Barik, teacher-researcher at the IPMC (CNRS-Université Côte d’Azur).

And, contrary to what some might think, this answer is not at all passive but proceeds from a learned “calculation”.

“Freezing is essential in stress management processes. It corresponds in fact to a state of hypervigilance which makes it possible to make the right decisions, in other words to develop the most relevant behavioral strategy: flee or fight.

Post-traumatic stress

Where things get complicated is when this type of reaction is triggered abnormally, in the absence of a proven threat.

“This is what happens in certain pathological situations: panic attacks, social phobias and especially post-traumatic stress disorders, says the researcher. People who have experienced traumatic events will thus tend to remain motionless in the face of a situation that reminds them of this trauma.

And the scientist cites the painful example of the victims of the July 14 attack in Nice. “At the sight of a white truck, and even if it poses no threat, they can remain frozen, in a state of amazement.” Very painful situations to experience and which call for therapeutic help.

“If one day we want to act on the triggering of the freezing in pathological situations – by targeting the areas involved – we already need to decipher the neural circuits involved in this reaction.”. And they remained to this day very little known.

Abnormal triggering

An important step in this field has just been taken by the researcher from Nice and his team in Sophia Antipolis, thanks to state-of-the-art approaches, and in particular a fairly recent technique called optogenetics (1). “It makes it possible to control neurons with just light. By activating certain neurons in mice, we were able to artificially make them relive these situations of stupefaction. And this is how we demonstrated the completely unexpected role of an area of ​​the brain classically linked to reward and reinforcement processes, in the modulation of freezing (2).”

From these discoveries, a question emerges: why the circuit of the reward, which defines at each moment the state of physical and psychic satisfaction in which we find ourselves, and thus allows us to promote “good” behaviors related to our fundamental needs? (drinking, eating, reproducing ourselves), is it also able to modulate fear reactions? Perhaps because they too are essential to our survival.

1. This equipment was funded by the Rotary Club through the Brain Research Federation and Operation Hope Ahead.

2. These studies, published in the journal Molecular Psychiatry, were supported by the Foundation for Medical Research and the National Research Agency.