This article was co-authored by Dr. Ruth Lanius and Lauren Rudolph
What is actually happening in our brain that makes us react to traumatic memories as though there is still danger, even if we are now safe? We conducted a first-of-its-kind study comparing the brains of people with and without PTSD when they recall traumatic memories. The results were fascinating and have important implications for treatment.
People with PTSD often struggle to feel safe and grounded when they recall traumatic memories, so we wanted to understand if there are differences in the connections between different levels of the brain that contribute to this. This is the first study to look at connections across the entire brain while people recall traumatic memories, rather than focusing on isolated brain regions.
What We Did in the Study
In this study, we asked this question: How are connections across brain levels different in people with Classic PTSD, people with the Dissociative Subtype of PTSD, and people who have experienced a traumatic event but did not develop PTSD?
All participants recalled a neutral memory and a traumatic memory during an fMRI brain scan. The traumatic memory involved a “moral injury” — a traumatic event involving a need to act against one’s own code of ethics, or witnessing someone else doing so. We compared the two groups (those with PTSD vs. no PTSD) and the two types of memories (neutral memory vs. traumatic memory).
What We Discovered About PTSD
So what did we discover? We found that people with PTSD (both Classic PTSD and the Dissociative Subtype of PTSD) had weaker connections between different layers of the brain that are involved in coordinating thinking, emotions, and physical responses. In people with PTSD, the survival brain (midbrain and cerebellum) is not connected enough to the reflective brain (the cortex), and these connections are critical for updating someone to a felt sense of safety.
In order to feel safe, the brain needs to update its predictions when necessary. The cerebellum is an important prediction center that anticipates how we will respond to events. The cerebellum constantly compares what the brain expected to happen with what actually happened. When the prediction of how we will respond (for example, predicting that we will run) does not align with present-day sensory information (for example, we stayed still because we went into freeze), the cerebellum tells the cortex that there was a prediction error. The cortex can then give the cerebellum updated information about what is happening in the present day (for example, that we are now safe) so that we predict better the next time. This is important so that one can truly feel safe after trauma.
In PTSD, these brain regions are less connected, so the prediction centers are stuck with information from the past, and they don’t receive the updated information that they are now safe.
Interestingly, there was another change in the cerebellum in people with PTSD when they recalled traumatic memories: there were increased connections within the cerebellum. This means that the cerebellum (the prediction center) ends up working on its own, rather than sending and receiving important updates from the cortex and other areas of the brain that can signal that we are now safe. Without these updates, the person remains “stuck in the past” without the ability to incorporate information from our present-day circumstances. For example, the sound of a firework causes a Veteran to run for cover, despite having heard the loud bang in the context of a safe family gathering.
Our study also helped explain why people with the Dissociative Subtype of PTSD often feel disconnected when recalling traumatic memories or facing reminders of their trauma. In these peoples’ brains, there were weaker connections between important parts of the brain. Their visual information, sensory information, and information about their body moving were not communicating well.
This explains why people with Dissociative PTSD may feel disconnected, even in light of current sensory information that tells them they are safe. For example, if the brain is not connecting the sight of our surroundings with what our body feels, that would be quite disorienting. Imagine trying to reach for a glass of water if you were unsure where your hand was!
Implications for Treatment
Overall, this study suggests that PTSD may involve problems with how the brain predicts and processes one’s experiences. When recalling traumatic memories, the PTSD-impacted brain may rely more on basic survival responses (e.g., fight, flight, freeze). At the same time, it may rely less on the brain functions that help people notice the present and realize the memory is in the past. This could help explain why traumatic memories in PTSD often feel so real and overwhelming – these memories feel as if they are happening right now, in the present. The changes in brain connections cause the brain to lose its capacity to update information, which keeps us stuck in the past.
To illustrate this, here is another example of how the brain responds to a fearful situation:
If you take the same route to work every day, your brain predicts things to be calm as normal and tunes out irrelevant stimulation. However, if you almost get hit by a car, this sudden experience causes a prediction error. In the next few days, it is typical to be cautious around that intersection.
Through vertical integration across the brain’s lower levels (brainstem and cerebellum) and higher levels (cortex), your brain updates after several safe commutes and understands that you are safe again.
However, the brain with PTSD does not update to safety. Instead, it gets stuck in the past and keeps predicting threat, in part because it lacks vertical integration across these levels of the brain.
This has important implications for treatment. It shows that treatment needs to restore vertical integration to improve the brain’s capacity to update information. This could help re-establish the sense that “I am safe” again. We will publish another Psychology Today post about treatment approaches that enhance vertical integration soon – stay tuned!
