Drug treatments and psychotherapy are only partially effective in treating post-traumatic stress disorder (PTSD). However, a recent study, published in Nature Neurosciences by Shan Siddiqi, a neuropsychiatrist at Harvard Medical School, and colleagues, suggests that changing the activity of a particular brain circuit would improve symptoms.
An accessible method for this is to direct pulses of magnetic energy to specific regions of the brain in order to interfere with the functioning of the neurons there. This technique, called “transcranial magnetic stimulation” (TMS), has demonstrated its effectiveness in treating the symptoms of pathologies such as Parkinson’s disease. But it is crucial to know the precise area the impulses should target and, for this, it is necessary to know which circuits are modified by the pathology in the brain.
To do this, researchers analyzed the brains of Vietnam War veterans. It was then a curious discovery that they revealed: certain soldiers who had suffered brain damage (following injuries or shocks) were less inclined than uninjured combatants to develop symptoms of PTSD. There are therefore areas of the brain whose lesion could protect against this syndrome.
Shan Siddiqi and his colleagues then mapped the network of these lesions, in order to identify which areas were associated with “protective lesions”. And it’s done: lesions linked to a cerebral network including the medial prefrontal cortex and the anterior and medial temporal lobes (within which we find the amygdala and the hippocampus, two structures essential to fear and memory) were correlated with a lower prevalence of post-traumatic stress syndrome.
Digging deeper, scientists found that among non-brain-injured veterans, the presence of PTSD was linked to hyperconnectivity within this circuit (too powerful neuronal connections between its different components, including the amygdala and the hippocampus). And when this hyperconnectivity was reduced using the transcranial magnetic stimulation technique, the symptoms of PTSD attenuated.
Small downside in the story, the SMT technique does not reach the deep layers of the brain, where structures such as the amygdala and the hippocampus are located. The ideal candidate to target is the medial prefrontal cortex, where magnetic pulses can easily reach. It plays an essential role in reducing the fear response, and its influence on the amygdala is involved in learning but also in the suppression of fear, two mechanisms disrupted in post-traumatic stress disorder. But all this does not make him the only candidate for this approach. By comparing each patient’s circuit to that identified by the mapping, it should be possible to determine the ideal target for the patient in question.
What the researchers tried to do in a patient suffering from PTSD resistant to other forms of treatment. Shan Siddiqi and colleagues compared the lesion mapping with magnetic resonance imaging scans of the patient’s brain in a resting state. To choose the personalized target for TMS, a region in the prefrontal cortex, where these two types of images overlapped best, was identified. After seven days of TMS targeting this area, the patient’s symptom severity score dropped from 10/10 to just 3/10. Enough to bring an impressive improvement to several aspects of this disabling syndrome. The next step will be to discover whether these same beneficial effects extend to a wider number of patients, which will be the focus of future research.
