EASY-TO-UNDERSTAND SUMMARY: THE DISSOCIATIVE SUBTYPE OF PTSD
What is the dissociative subtype of PTSD?
In recent years, researchers (including members of our team!) have helped to identify a dissociative subtype of PTSD, which has some unique features in comparison to the more commonly recognized, classic form of PTSD. For example, classic PTSD tends to involve symptoms of over-arousal (e.g., increased heart and breathing rates), and active defensive responses that may help someone escape danger (e.g., fight/flight).
In contrast, the dissociative subtype of PTSD tends to involve symptoms of blunted or dulled arousal (e.g., slowed heart and breathing rates), and passive defensive responses (e.g., dissociation). These passive defense responses might include emotional detachment and/or a sense of disconnection from the body/sense of self (e.g., feeling disconnected from their emotions, or feeling as if they are outside their body). These responses can help someone withstand or endure traumatic events when physical escape is not possible. As a result of dissociation, the experiences may seem duller, or as if the trauma were not actually happening to them.
In trying to understand this type of response, we could compare it to how a mouse might “play dead” when cornered by a cat – its bodily functions slow down so that they appear limp and lifeless, and the cat loses interest. During passive defensive responses, human bodily functions slow down in a similar way.
Our research team is interested in learning more about the dissociative subtype of PTSD, and how it might differ from the classic type. Having a better understanding of any differences between the two could help physicians and therapists select the most effective treatment for individual patients.
How and why would two people in the same accident have different trauma symptoms?
Lanius RA, Hopper JW, & Menon RS. (2003). Individual Differences in a Husband and Wife Who Developed PTSD After a Motor Vehicle Accident: A Functional MRI Case Study. Am J Psychiatry 160:4 (April)
This paper describes a married couple who were both diagnosed with acute PTSD after being in the same serious, multi-vehicle car accident. Immediately after the collision, the couple were trapped in their car for a brief period of time, and the husband broke the windshield so they could escape. Afterward, despite having gone through the same traumatic event, their symptoms differed, so we wondered how this might be reflected in their brain activity.
Prior to the accident, the husband had no mental health concerns and he had not experienced any trauma. During the accident, he reported feeling very distressed. The day after the accident, he began experiencing nightmares and flashbacks (i.e., feeling like the accident were happening in the present), he became distressed when thinking about the accident, felt irritable and jumpy, avoided things that reminded him of the accident, and both his sleep and concentration were impacted.
Prior to the accident, the wife had experienced childhood trauma. Throughout her life, her mental health had been fairly good, having only experienced depression after giving birth to her first child, and mild bouts of panic/anxiety. During the accident in question, she felt like she was “in shock” and she could not move because she felt “completely frozen”. Afterward, like her husband, she also developed flashbacks and nightmares, but instead of feeling distress, she felt “numb” and “frozen” during these times. Both her sleep and concentration were impacted, she avoided reminders of the accident, and she felt irritable and easily angered.
To learn about how their brains may have processed the accident differently, we asked them both to complete fMRI (functional magnetic resonance imaging) brain scans. In the scanner, they were asked to bring to mind their memory of the accident, while the scanner recorded how their brains were working. Both of them reported having experiences that were similar to their experiences during the accident.
For example, the husband recalled feeling anxious and jumpy, and he remembered thinking about how to escape, and then breaking the windshield (note his active defense reaction). During the brain scan, his heart rate increased (preparing his body to act), and his brain activity increased in a number of areas, including areas involved in emotional alarm, planning, physical action, and vision (again, reflecting his active response of fight/flight). After 6 months of trauma treatment, he no longer had PTSD.
His wife’s experience during the fMRI scan was quite different, and again, it reflected her original experience. During the brain scan she felt frozen and numb, her heartbeat did not increase, and her brain activity increased only in an area used for vision (note that this reflects a “passive” defense or “freeze” reaction – one that can help a person withstand the trauma when escape feels impossible). After 6 months of trauma treatment, unfortunately, she still had significant PTSD.
These images show the results of our fMRI brain scans, with the patches of yellow showing areas of greater brain activity in response to reminders of the car accident. We can see that a number of areas in the husband’s brain are quite active, while the wife’s brain activity seems largely shut down. This brain activity help explain their differing symptoms.
Image from: Lanius, Hooper & Menon, 2003
This couple, who experienced the same traumatic event at the same time, gives us nice examples of the 2 different types of PTSD. While the husband seemed to experience the more commonly recognized, classic form of PTSD that centres around fight or flight, his wife’s symptoms were in line with the more recently identified dissociative subtype of PTSD, which typically centres around emotional “shut-down” or “freeze” responses. We presumed the different reactions they had to the accident were caused by different brain activity, and this was supported by their fMRI scans. Previous research suggests that individuals who experience emotional numbness often struggle to process the trauma(s) successfully, so this may help explain why the wife’s recovery was different from the husband’s. This study helps illustrate the individual responses possible following a traumatic event.
What are the differences between classic PTSD and the dissociative subtype of PTSD?
Lanius RA, Vermetten E, Loewenstein RJ, Brand B, Schmahl C, Bremner JD, and Spiegel D. (2010). Emotion Modulation in PTSD: Clinical and Neurobiological Evidence for a Dissociative Subtype. Am J Psychiatry. 2010 June; 167(6): 640–647. doi:10.1176/appi.ajp.2009.09081168.
This paper was written before the dissociative subtype of PTSD was officially recognized. Here, we presented evidence that this subtype does exist, along with a description of symptoms and brain changes that differ between it, and those seen in the more commonly recognized non-dissociative type PTSD. We discuss the dissociative subtype of PTSD as being a type of over-control of emotions (via “shutting off” or “numbing out” of emotions), while the non-dissociative type of PTSD represents under-control (e.g., becoming very easily alarmed, ready to fight or flee).
This paper also discusses how the differences in brain activity affect emotions differently. We discuss a model, or a way of thinking, that helps explain these differences. For example, this model suggests that hyperarousal (i.e., becoming easily alert/distressed) could be understood as a failure of upper-level brain areas (i.e., those responsible for more complex functions, like attention, planning) to control the activity of lower-level brain areas (i.e., those responsible for more basic functions, like heart rate, fear responses). In contrast, for the dissociative subtype of PTSD, these same lower-level brain areas might be over-controlled (and essentially turned off) by upper-level brain areas, resulting in flat emotion and slowed heart rate.
Overall, recognition of the two types of PTSD will be important when clinicians assess their patients, and when a treatment is selected. This information also highlights the need to include a plan for the treatment of dissociative symptoms into the standard PTSD treatment plan.
How is brain activity in the insula different between people without PTSD, people with classic PTSD, and people with the dissociative subtype of PTSD?
Harricharan S, Nicholson AA, Thome J, et al. (2020). PTSD and its dissociative subtype through the lens of the insula: Anterior and posterior insula resting‐state functional connectivity and its predictive validity using machine learning. Psychophysiology, 57:e13472. https ://doi.org/10.1111/psyp.13472
The identification of different types of PTSD has allowed us to begin understanding some important differences in the symptoms people experience. For example, while intrusive memories and hypervigilance tend to be prominent in classic PTSD, people with the dissociative subtype experience symptoms such as depersonalization and derealization (e.g., feeling as if they or their surroundings are distorted or not real). Our team is always looking to find neurological reasons to help explain these differences. In this study, we looked at the insula. The insula is a brain structure that is important for processing emotions, yet it isn’t clear how its function might differ between the two types of PTSD. Our goal in this study was to begin investigating potential differences.
This was a “resting state” fMRI (functional magnetic resonance imaging) brain scan study, which involved participants letting their minds wander naturally, not focusing on anything in particular, while the fMRI scanner captured what brain areas were being used. Using these resting state brain scans, we compared three groups of participants – individuals with the dissociative subtype of PTSD, those with the classic form of PTSD, and those with no history of mental health diagnoses (i.e., the “control” group). Interestingly, we found that how the insula was connected to other areas of the brain was different in each group.
The control group showed more connections between the insula and certain brain areas involved in monitoring the environment and processing emotions. These connections may help people from this group safely navigate their surroundings with less effort, and to quickly judge the emotional importance of information from their senses (e.g., Quickly recognizing that a loud noise was simply fireworks on a day of celebration).
In contrast, the classic PTSD group showed more connections between the insula and lower brain areas, including the periaqueductal gray (see our “Sense of Self” Summaries section for more information on this structure). These brain areas play an important role in instinctual, defensive responses (e.g., fight/flight), so having more connections may contribute to their symptoms of hypervigilance (e.g., being overly watchful for danger) and hyperarousal (e.g., being easily startled).
Finally, participants in the dissociative subtype group showed more connections between the insula and brain areas involved in processing sensations from the internal organs (e.g., stomach pain), and areas involved in implicit memories (i.e., memories that don’t require intentional remembering, such as how to ride a bike, or perhaps “taking cover” when you hear someone yelling).
Next, to more clearly identify the differences we found, we used a type of analysis called “machine learning”, which uses computers to try to recognize complex patterns of information that humans might not notice. In the medical field, machine learning can be used to help diagnose certain physical and mental health conditions. Using machine learning in our study, we were excited to realize we could accurately identify the group to which a participant belonged (i.e., dissociative or classic PTSD, or control group) just based on their brain activity – the different patterns were that clear. This means that this type of resting state brain scan may, one day, be able to help clinicians clarify a patient’s precise PTSD diagnosis, and help in selecting the most effective treatment.
A new model of dissociation:
How can this 4-D Model help clinical practice?
Lanius, R. (2015). Trauma-related dissociation and altered states of consciousness: a call for clinical, treatment, and neuroscience research. European Journal of Psychotraumatology 2015, 6: 27905 -http://dx.doi.org/10.3402/ejpt.v6.27905
Trauma-related dissociation can be described as a feeling of disconnection from our own body, our thoughts/feelings, and/or our surroundings. Its purpose is to provide relief from overwhelming emotional and physical distress associated with a traumatic experience. This paper describes a new way of looking at trauma (i.e., the “4-D” model), that can help us understand trauma-related dissociation and other altered states of consciousness.
To begin, this model divides trauma-related mental health symptoms into two categories: 1) symptoms that happen while someone is fully conscious/aware (e.g., trauma memories, increased heart rate, feeling that other people are dangerous), and 2) symptoms that occur during dissociation/altered states of consciousness. Within this second category, symptoms can be clustered into four sub-categories: symptoms that impact: 1) time (e.g., flashbacks to past traumas), 2) thoughts (e.g., hearing voices of past abusers), 3) the body (e.g., hands feeling disconnected from our body), and/or 4) emotion (e.g., feeling emotionally dead or numb). Dividing symptoms in this way can help us better identify and understand symptoms of dissociation.
Based on this 4-D model, any treatment for trauma survivors should include building a sense of self, because this may help them to simply remember past events, rather than reliving them as flashbacks. Keeping this model in mind, treatment should also include: encouragement to establish safe relationships (including the one with their therapist), building mindfulness skills and emotion regulation skills, learning how to better manage distress, and increasing their ability to tolerate positive emotions (which can often feel unsafe for trauma survivors).
It will be important for future research to investigate how these four dimensions of dissociation might be represented in the brain and how it functions. Understanding this could lead to better and more specific treatment for the dissociative subtype of PTSD.
How is amygdala brain activity different in people without trauma, people with classic PTSD, and people with the dissociative subtype of PTSD?
Nicholson AA, Densmore M, Frewen PA,Théberge J, Neufeld RWJ,McKinnon MC, and Lanius RA. (2015). The Dissociative Subtype of Posttraumatic Stress Disorder: Unique Resting-State Functional Connectivity of Basolateral and Centromedial Amygdala Complexes Neuropsychopharmacology (2015) 40, 2317–2326
For this study, we compared fMRI (functional magnetic resonance imaging) brain scan data from three groups of participants – individuals with the dissociative subtype of PTSD, those with the classic form of PTSD, and those with no history of mental health diagnoses. During the fMRI scan, participants were asked to let their minds wander naturally, not focusing on anything in particular, as the scanner captured what brain areas were being used (i.e., a “resting state” scan). In particular, we were interested in learning more about connections to the amygdala - a structure in the brain that helps us detect danger quickly, but tends to become overly sensitive in PTSD.
When comparing our two PTSD groups, people in the dissociative PTSD group had more connections leading to a specific area of the amygdala than did people in the classic PTSD group. Interestingly, this particular area is involved in emotion regulation, and we wonder if this difference might help explain the emotional “shut-down” or detachment often seen in the dissociative subtype (perhaps an over-regulation of emotions). We also found that the dissociative group had more connections to areas involved in depersonalization and derealization (i.e., feelings of disconnection from the self and one’s surroundings), helping to explain these particular symptoms of PTSD.
Overall, these findings emphasize the neurological differences between the different subtypes of PTSD, and the importance of selecting treatments accordingly.
How are brain connections to the pulvinar area different in people without PTSD, people with classic PTSD, and people with the dissociative subtype of PTSD?
Terpou BA, Densmore M, Théberge J, Frewen P, McKinnon MC, Lanius RA. Resting-state pulvinar-posterior parietal decoupling in PTSD and its dissociative subtype. Hum Brain Mapp. 2018;00:1–13. https://doi.org/10.1002/hbm.24242
The pulvinar nuclei are brain structures that play an important role in more complex brain functions, for example, those needed for effective social interaction. The pulvinar nuclei act as a relay station – when they receive information, they send it back out to other important brain areas. In this study, we used “resting state” fMRI (functional magnetic resonance imaging) brain scans to learn more about how the pulvinar nuclei might work differently in three groups of participants – those with classic PTSD, those with the dissociative subtype of PTSD, and participants with no mental health diagnoses (our “control” group).
A resting state fMRI scan is one during which participants are asked to let their minds wander naturally, so that they’re not reflecting on any one thing in particular; meanwhile, the fMRI brain scan records how their brain is functioning. Knowing that the pulvinar nuclei are generally less active in people with PTSD, we wanted to learn about how these structures work while people’s minds are in a resting/mind-wandering state, as this may have an effect on important connections within the brain.
In comparison to our control group, both PTSD groups showed less connection between the pulvinar nuclei and other brain areas that are used to help pull information together from each of our senses. By gathering this type of sensory information, we become more aware of our body’s different states (e.g., I’m hungry/tired/scared), and our surroundings (e.g., Where am I positioned within this room? Where are the other objects/people located?). Interestingly, people with the dissociative type of PTSD had the weakest connections of the three groups. This may help explain the tendency for people in this group to feel disconnected from their bodies because information from their senses isn’t being integrated as well.
Also, this study showed that both PTSD groups had fewer connections between the pulvinar nuclei and certain brain areas involved in emotions/thoughts during social interactions. This helps us understand some of the challenges many people with PTSD experience in social situations (e.g., “reading” another person’s emotions accurately, imagining how they may be feeling).
As always, knowing this type of information – i.e., differences in brain function and connection related to PTSD – can help physicians and therapists develop and select more effective treatments for their patients
