A recent study published in Behavioral neuroscience offers new insights into the relationship between brain structure and post-traumatic stress disorder (PTSD). The study found that smaller volumes in specific regions of the hippocampus, a brain structure involved in memory and learning, are associated with reduced severity of PTSD symptoms over time. This counterintuitive finding suggests a complex relationship between hippocampal structure and PTSD symptoms, particularly in how these brain regions may influence symptom improvement.
PTSD is a mental health problem that can develop after experiencing or witnessing a very distressing or traumatic event. It is characterized by symptoms such as reliving the trauma through flashbacks or nightmares, avoiding reminders of the event, emotional numbing, and increased excitement or anxiety. PTSD can have a significant impact on a person’s daily life, affecting their ability to function normally in social, occupational, and other areas.
Previous research has suggested that the hippocampus may be linked to PTSD. However, the relationship between hippocampal structure and long-term changes in PTSD symptoms is less clear. The new study aimed to explore whether specific subfields of the hippocampus could predict changes in PTSD symptoms over an extended period of time, thereby providing deeper insights into the neurobiological mechanisms underlying the disorder.
“We were interested in this topic because, among our veterans with PTSD, we wanted to predict who was most likely to reduce PTSD symptoms over time and who was most likely to have chronic symptoms or who ‘worse,’ said study author Joseph DeGutis, a health care industry expert. scientist at the VA Boston Healthcare System and associate professor at Harvard Medical School.
“Previous studies have consistently implicated the hippocampus, a brain structure essential for learning and memory, as playing an important role in the development and maintenance of PTSD. Advances in structural analysis of MRI data have also enabled automated segmentation of hippocampal subregions (subfields) that play different roles in learning and memory (e.g., fear learning or model completion).
For their study, the researchers recruited 252 post-9/11 veterans, including 159 with PTSD and 93 without. Participants underwent two assessments approximately two years apart. During these assessments, PTSD symptoms were measured using the Clinician Administered PTSD Scale (CAPS), a widely used diagnostic tool. Additionally, magnetic resonance imaging (MRI) scans were performed to measure the volumes of different subfields of the hippocampus, particularly the CA1 and CA3 regions of Cornu Ammonis (CA), and the dentate gyrus.
To ensure the accuracy of their results, the researchers used an advanced imaging analysis tool called FreeSurfer, which provides detailed volumetric measurements of hippocampal subfields. They also took into account potential confounding factors such as age, gender, head size and type of scanner.
Contrary to the initial hypothesis, the researchers found that lower volumes in the CA1 and CA2/3 body regions of the hippocampus were associated with greater reductions in PTSD symptom severity over time. These associations were specific to changes in avoidance and numbing symptoms, rather than reoccurrence or hyperarousal symptoms. This suggests that smaller volumes in these hippocampal subfields might somehow facilitate improvement in some PTSD symptoms.
“Several previous MRI studies have shown that a larger overall hippocampus (brain structure essential for learning and memory) protects the individual from developing PTSD after exposure to a traumatic event,” DeGutis told PsyPost. “However, our results show that, if you develop PTSD, smaller volumes of hippocampal subregions (CA1, CA3) are predictive of PTSD symptoms. improvement over time.
“In other words, a larger hippocampus and its subregions may be beneficial in preventing you from developing PTSD, but if you develop PTSD, larger hippocampal subregions may be linked to more chronic symptoms/ aggravated.”
“We were surprised to find that smaller hippocampal subfields predicted better PTSD outcomes! » said DeGutis. “This suggests that the risk factors for developing PTSD are different from the factors that predict whether you will recover from PTSD once you have it. Our findings provide a more complex and nuanced understanding of the role of the hippocampus in PTSD. »
Interestingly, the study did not find significant associations between hippocampal volume and other factors such as combat exposure, treatment history, or time since deployment, which indicates that the observed relationships were robust and not influenced by these variables.
The study challenges the traditional view that larger hippocampal volumes are always better in the context of PTSD. But as with any study, there are certain limitations to consider. The sample was predominantly male veterans, raising questions about the generalizability of the results to other populations, such as women or civilians.
Another limitation lies in the timing of the assessments. The first assessment took place an average of three years after participants returned from deployment, meaning the study did not take into account changes in hippocampal volume immediately after trauma. This makes it difficult to determine whether the smaller hippocampal volumes were a pre-existing condition or a consequence of prolonged PTSD.
The long-term goal of the research is “to try to determine, in people diagnosed with PTSD, who gets better over time and who doesn’t,” DeGutis said. “This has important mechanistic implications for models of PTSD, but also tells us who to target with targeted treatments.” It is expensive for everyone to have a brain MRI and we are currently testing whether these observed brain differences can be seen on memory tasks that may be widely accessible.
The study titled “Less is More: Smaller Hippocampal Subfield Volumes Predict Greater Improvements in Post-Traumatic Stress Disorder Symptoms Over 2 Years” was authored by Joseph DeGutis, Danielle R. Sullivan, Sam Agnoli, Anna Stumps, Mark Logue, Emma Brown, Mieke Verfaellie. , William Milberg, Regina McGlinchey and Michael Esterman.