Almost ten years since the team of neuroscience researcher Pierre Gagnepain began its dive into the mazes of the brains of survivors of the November 13 attacks. Since 2015, many of them have experienced severe anxiety and remain haunted by intrusive thoughts – also called flashbacks – of images, sensations, sounds or smells associated with the trauma. This often results in disorders of mood, attention, concentration or sleep. But in the scientific world, this post-traumatic stress disorder (PTSD) remains shrouded in mystery. Why do some people develop it and not others? What is actually happening in the brain?
In the hope of providing some answers, around a hundred volunteers agreed to undergo, three times in ten years, a series of brain tests under the impressive magnetic resonance imaging (MRI) machine. On January 8, the researchers of this study called Remember – which is part of the larger November 13 program led by Inserm and the CNRS whose objective is to study collective and individual memories of the attacks – published their latest results in the magazine Sciences Advances. If the images of brain activity have made it possible to discover that people suffering from this disorder are those who fail, via control mechanisms, to inhibit intrusive thoughts, they have above all revealed that this dysfunction is not permanent. : in cured people, the plasticity of these mechanisms returns to normal and functions again. For Pierre Gagnepain, neuroscience researcher at the Cyceron imaging center in Caen and scientific manager of the Remember program, this study could notably open the way to new therapies.
Until now, what was known about post-traumatic stress disorder?
Initially, it was perceived as a learning difficulty: imagine that you are afraid of spiders and that one morning, you come face to face with a spider in your kitchen. You will be afraid, but the next day, when you come back, you will realize that she is no longer there. Your memory will therefore be updated with this new context without danger. For a person whose learning functions normally, these new memories (of the absence of the spider and of danger) will overwrite the old one. PTSD would then be a problem of erasing this memory of fear by new situations. But this theory does not explain why some people develop this disorder and others do not.
Our hypothesis focused instead on the brain’s difficulty in blocking and inhibiting the intrusive image. Example: if you are working and suddenly your vacation memories come to disturb you, you will need a mechanism to refocus and ignore these thoughts. It is a form of active forgetting. What if, in people who develop PTSD, the emergence of negative memories in inappropriate contexts comes from an inability to block and silence them?
How did you go about supporting this hypothesis?
We implemented a “think/no-think” task, also called memory suppression task. The principle is simple: people are asked to learn pairs of stimuli by heart, for example the word “table” with the image of a ball. So, if we present the word “table”, it is the image of the ball that automatically emerges. During the “think” condition, people must visualize the associated object in as much detail as possible. In the “no-think” condition, on the contrary, they must do everything to maintain attention on the word and prevent the image from emerging by emptying their mind. In 2016, we observed that this brain inhibition function was perfectly preserved in people who had not developed PTSD, but that it was completely altered in people who suffered from it.
-But according to the results of your study published on January 8, this alteration is not immutable…
It has in fact been observed that these mechanisms return to normal in people in remission. Except that it was difficult to know precisely whether it was a cause or a consequence. According to our results, it seems that the improvement of these mechanisms predicts the future reduction of intrusive memories of the trauma.
Beyond reducing symptoms, resilience is also the brain’s ability to limit the negative effects of stress. By focusing on the hippocampus, a region very sensitive to the effects of stress, it was observed that in people who had chronic PTSD, its volume tended to decrease. In other words, being stressed and afraid all the time for five years had reduced the size of the hippocampus, which allows us to separate memories well and prevent the memory of fear from arising in seemingly obvious situations. safe. But it was mainly discovered that his atrophy was interrupted at the same time as the PTSD. Basically, nothing is written in stone. We are not going to suffer all our lives. And if these mechanisms are dynamic, that means that we can develop and strengthen them to protect ourselves.
Which means that we could imagine new approaches to the treatment of PTSD?
Quite. Currently, most treatments focus on re-exposure to the trauma. We seek to relive the traumatic event to modify its meaning and attenuate the emotional response. Our results suggest that we could complement these existing treatments by stimulating control and inhibition mechanisms, without needing to refer to emotional or traumatic images.
