Neuroscientists are starting to unravel the amygdala’s complexity, shedding new light on PTSD

A new study published in Translational Psychiatry provides evidence that posttraumatic stress disorder may be linked to altered communication between specific parts of the amygdala and other brain regions. The findings suggest that one part of the amygdala in particular shows distinct patterns of connectivity in people with the condition, which may help explain difficulties with emotional regulation, sensory processing, and self-related thought often seen in PTSD. This research highlights how focusing on the smaller subdivisions of the amygdala may deepen scientific understanding of PTSD’s neural foundations.

The amygdala is often described as the brain’s “fear center,” due to its well-established role in detecting threats and triggering fight-or-flight responses. However, scientists now recognize that it plays broader roles in how we experience emotions, respond to rewards, and process sensory information. Previous research has shown that the amygdala functions differently in people with PTSD, but many studies have treated the amygdala as a single unit. This approach may be overlooking subtle but important differences in how its internal structures behave.

In reality, the amygdala is made up of several distinct regions, or subnuclei, that connect to different parts of the brain and support different functions. These subnuclei include the basolateral, centromedial, and superficial regions, each of which is thought to contribute uniquely to emotion, behavior, and bodily responses. The new study aimed to clarify how these substructures connect with the rest of the brain in people with PTSD compared to those without trauma exposure. By focusing on these smaller components, the researchers hoped to uncover more precise patterns of brain function associated with the disorder.

“Most people have heard of the ‘fight or flight’ response—how your body reacts when you’re scared. A key player in that response is a part of the brain called the amygdala, which is also heavily involved in PTSD,” said study author Elizabeth Haris of the University of Melbourne.

“In most research, the amygdala is treated as though it’s one single structure. But in reality, it’s made up of several smaller regions that may each play different roles. We wanted to look more closely at how these smaller regions connect to other parts of the brain. By comparing people with PTSD to those without trauma exposure, we hoped to see whether these connection patterns could give us new insights into how PTSD affects the brain.”

For their study, the researchers analyzed brain scans from 129 adults: 65 individuals with PTSD and 64 non-traumatized participants. The PTSD group included civilians who had experienced a variety of traumas. Nearly half reported trauma in childhood, and many also had conditions like depression or anxiety. None of the participants had a history of psychosis, traumatic brain injury, or substance dependence.

Instead of using data from a typical resting-state brain scan, the researchers used a method known as task-derived intrinsic functional connectivity. Participants had completed five separate cognitive and emotional tasks while undergoing functional magnetic resonance imaging. The researchers removed task-related brain activity from the scans to isolate underlying connectivity patterns that persist across different mental states. This approach has been found to provide reliable information about how brain regions interact, even when tasks are involved.

The researchers then divided each participant’s amygdala into three substructures in each hemisphere: the basolateral, centromedial, and superficial regions. Using these as starting points, they measured how strongly each region was functionally connected to other areas of the brain. Functional connectivity refers to how synchronized the activity of different brain regions is over time.

The main finding was that the patterns of brain connectivity linked to the basolateral region of the amygdala were significantly different between people with PTSD and those without trauma exposure. In contrast, no group differences were found for the centromedial or superficial regions.

“One surprise was that we only found clear differences in brain connectivity for one part of the amygdala—the basolateral amygdala—and not the other two regions we looked at,” Haris told PsyPost. “This shows why it’s so important to study these smaller subregions individually, because they don’t all behave the same way. Notably, the lack of differences in the other areas could also mean a few things. It might be because those regions are physically smaller and harder to measure, or because they’re more active in specific situations rather than when the brain is at rest.

“For example, one of these regions, the centromedial amygdala, is especially linked to generating responses, so its role might stand out more if people were doing a task instead of just resting in the scanner. Overall, this tells us there’s still so much to learn. Each part of the amygdala has its own role, and exploring those differences could help us uncover even more about how PTSD affects the brain.”

For individuals with PTSD, the basolateral region showed reduced connectivity with several cortical areas, including the precuneus, posterior cingulate cortex, precentral and postcentral gyri, and the superior parietal lobe. These brain regions are typically involved in bodily sensation, movement, attention, and self-referential thought—mental processes involved in understanding one’s own feelings or sense of identity. Reduced connectivity in these networks may contribute to PTSD symptoms such as emotional numbness, identity disturbance, or impaired control over bodily reactions.

At the same time, the PTSD group showed increased connectivity between the basolateral amygdala and a different set of brain areas, particularly in the brainstem, cerebellum, and right pallidum. These areas are associated with arousal, threat detection, motor control, and processing rewards or punishments. For example, the brainstem helps regulate automatic functions like heart rate and stress responses, while the pallidum is linked to motivation and reward-seeking behavior.

Together, these findings suggest that the basolateral amygdala may be more strongly tied to systems involved in alertness and stress in people with PTSD, while being less engaged with networks responsible for self-awareness and sensory regulation.

The researchers also looked at within-group differences. In the non-traumatized group, the basolateral amygdala had stronger connections to cortical regions, while the superficial region tended to connect more with subcortical areas. In contrast, for the PTSD group, the basolateral region had stronger connections to both cortical and subcortical areas than the other amygdala subregions did, indicating its dominant role in altered connectivity patterns.

These group differences held up even after accounting for factors like age and education. The results were also not explained by common co-occurring conditions such as depression or generalized anxiety disorder.

“The main takeaway is that the amygdala is much more complex than we often think,” Haris said. “Most people know it as the ‘fear center’ of the brain, or the place that drives the fight-or-flight response. But our study shows it’s also involved in many other processes. When we look more closely at its smaller parts, we see links not only to fear and arousal, but also to things like how we process sensory information, how we respond to rewards, how we think about ourselves, and even how we integrate thoughts and movements. In short, the amygdala isn’t just about fear—it plays a role in a wide range of experiences and behaviors.”

The study also provides support for the idea that PTSD may involve imbalances in how different brain networks communicate, particularly those related to emotional and bodily regulation. The basolateral amygdala appears to sit at the center of these altered patterns, acting as a hub that is either underconnected to some cortical systems or overconnected to brain regions associated with arousal and vigilance.

This pattern may help explain why people with PTSD often report feeling constantly on edge or disconnected from themselves or their bodies. The increased links between the amygdala and brainstem could reflect heightened threat detection, while the reduced links with areas like the precuneus might relate to difficulties with self-reflection or integrating sensory input.

By identifying these more specific changes in brain communication, the findings support the view that PTSD is not a uniform disruption of the fear system, but a more nuanced shift in how various brain regions interact.

“Like all research, our study has some limitations,” Haris noted. “The biggest one is the comparison group we used. When studying PTSD, you ideally want to compare people with PTSD to people who have also experienced trauma but not developed PTSD. In our case, the comparison group wasn’t quite that ‘gold standard,’ so it’s important to keep that in mind.”

Despite these limitations, the study offers a detailed look into how different parts of the amygdala function in PTSD and how they relate to broader brain systems. The findings support the idea that the amygdala plays a wider role than just fear detection. By focusing on its internal structure, researchers may gain a clearer understanding of the diverse symptoms of PTSD and open new paths for treatment targeting specific brain networks.

“Looking ahead, our next steps involve using a more advanced type of MRI scanner, called a 7T scanner,” Haris said. “This technology gives us much higher resolution images of the brain, which means we can see the amygdala’s subregions in even greater detail than before. The study we’ve just discussed used a standard 3T scanner, which is still very valuable, but the 7T scanner allows us to push the boundaries further and to even better understand how these subregions of the amygdala contribute to PTSD. We’ve already started this work, and we’re excited to share those findings soon!”

“I’d just like to highlight that this study was truly a team effort,” she added. “It took many years and countless hours of data collection, and it wouldn’t have been possible without the dedication of both the research team and the participants who generously gave their time. We’re very grateful to them, because their contributions are what make it possible to move this research forward and deepen our understanding of PTSD and, most importantly, how to better help people who are going through it.”

The study, “Functional connectivity profiles of amygdala subregions in posttraumatic stress disorder,” was authored by Elizabeth M. Haris, Richard A. Bryant, Kim L. Felmingham, Leanne M. Williams, and Mayuresh S. Korgaonkar.