EASY-TO-UNDERSTAND SUMMARY: SENSE OF SELF AND
THE DEFAULT MODE NETWORK
What is the default mode network, and why is it important to consider in trauma and PTSD?
Trauma can have a dramatic impact on our sense of self – both in how we think about ourself as a person (e.g., I’m bad, not worthy), and how we experience our body (e.g., I feel dead inside; my hands don’t feel attached to my body). The following studies investigate how trauma contributes to changes in the sense of self, which seems to involve part of the brain referred to as the “Default Mode Network”, or DMN.
The DMN is made up of a number of brain regions that communicate with one another while we are in a state of wakeful rest – i.e., when we are awake but letting our mind wander. It appears to be involved in self-reflection (e.g., thinking about who we are and our life events), recalling memories, social connection, and an awareness of our body/senses that helps us know where we are located in space.
Knowing this, our group and others have hypothesized (i.e., assumed or concluded) that the DMN plays a very important role in the sense of self. Unfortunately, research has shown that brain activity in many areas of the DMN can be affected by chronic trauma and dissociative symptoms (i.e., feelings of disconnection from oneself and/or one’s surroundings). It would make sense then, that if these important brain areas were affected, the sense of self might be affected as well.
In the following studies, we wanted to learn in more detail how trauma might impact the DMN. In order to do so, we used fMRI (functional magnetic resonance imaging) brain scans, which allowed us to see which brain areas were being used during “wakeful rest”, and how these areas communicated with one another. For these studies, we asked participants to let their minds wander naturally while they were in the scanner, so that they were not thinking about any one thing in particular. This is often referred to as a “resting state” procedure. During these scans, we were expecting to see some significant differences between people with and without PTSD. Read on for more information about the results of our DMN studies.
How is brain activity in the default mode network different in people with no mental health diagnoses compared to people with PTSD?
Bluhm RL, Williamson PC, Osuch EA, Frewen PA, Stevens TK, Boksman K, Neufeld RWJ, Théberge J, Lanius RA. (2009). Alterations in default network connectivity in posttraumatic stress disorder related to early-life trauma. J Psychiatry Neurosci 2009;34(3).
To begin investigating the impact of trauma/PTSD on the default mode network (DMN), we completed fMRI brain scans with two groups of women – those diagnosed with PTSD related to childhood abuse, and those with no history of mental health diagnoses (our “control” group). For this study, we focused on brain regions within the DMN, whose function can be impacted by trauma/PTSD. In particular, we thought PTSD might impact the posterior cingulate cortex (PCC)/precuneus – brain areas thought to be involved in memory retrieval.
Using an eyes-closed, “resting state” procedure (a.k.a., mind-wandering) during our brain scans, we found some significant differences between our groups. For example, in our control group, this mind-wandering task activated a number of brain areas within the DMN – suggesting that some self-reflection may have been taking place (e.g., body awareness, thinking about their day/life). In comparison, for those in the PTSD group, far fewer connections were activated within this same brain area. We hypothesized (i.e., assumed or concluded) that these differences may be related to a “loss of self” – a common symptom for people with PTSD. This loss of self often includes confusion about what type of person they are, their worth, and the connection between their mind and body.
The brain images below are from the study when participants were asked to let their minds wander naturally. The orange and yellow patches show areas of more connection and activity. In comparison to the “control” group, the image from the PTSD group shows much less activity. Again, we believe this to be one of the consequences of chronic trauma – fewer connections within the DMN.
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How are connections in the brain's default mode network different in people with childhood trauma?
Daniels JK, Frewen P, McKinnon MC, Lanius RA. (2011). Default mode alterations in posttraumatic stress disorder related to early-life trauma: a developmental perspective. J Psychiatry Neurosci, 36(1); DOI: 10.1503/jpn.100050
At the time of writing this paper, scientific research was just starting to link long-term childhood abuse to brain changes within the default mode network (DMN). The DMN is made up of a number of brain regions that communicate with one another, and among other tasks, it seems to play an important role in self-reflection (e.g., thinking about who you are/your life).
Studies with adults with PTSD related to childhood abuse show that connections within their DMNs looked very similar to the connections seen in healthy children aged 7 to 9 years. This suggests that prolonged abuse in childhood may interfere with the full development of the DMN. Knowing that many of the brain regions within the DMN are also used for other functions and abilities (e.g., memory for our own life events, the ability to understand how others are feeling, the ability to anticipate future events), research will be needed to investigate how childhood abuse might affect these functions as well.
We suggested that research should include studies that follow people from childhood through adulthood to help us fully understand the impact of abuse on all of these brain functions and connections. Without this type of research, we can only make educated guesses. See our other studies/papers in this section to see how our team is trying to build on this type of research.
What 4 differences are found in the brain's default mode network that affect one's sense of self in people with PTSD?
Lanius RA, Terpou BA, and McKinnon MC. (2020). The sense of self in the aftermath of trauma: lessons from the default mode network in posttraumatic stress disorder. European Journal of Psychotraumatology, VOL. 11, 1807703,
Self-reflection can be described as thinking about our own thoughts, behaviours, emotions, and experiences. It can help us develop a sense of who we are - a sense of self. Unfortunately, trauma tends to negatively impact our sense of self. This paper summarizes previous research that attempts to help explain how this happens.
To begin, we know that in healthy adults, self-reflection largely takes place within a group of connected brain areas called the Default Mode Network (DMN). In addition to self-reflection, the DMN can also help people imagine how another person might be feeling or thinking. This ability is essential for experiencing empathy, but it may also help us avoid dangerous people with bad intentions. Throughout our research, we have learned that the DMN looks and works quite differently in people with PTSD, especially when their PTSD stems from childhood trauma - a time when the brain is still developing.
Firstly, while the DMN in a non-traumatized person is typically quite active when their mind is at rest (i.e., awake, but not actively “thinking”), for people with PTSD, connections and activity within this brain network tend to be weaker at rest. This may help explain the poor sense of self that many traumatized people have. Further, we wonder if these weaker connections may help explain why people with a history of abuse often end up in additional abusive relationships. Perhaps their DMN isn’t able to pick up on subtle cues that certain people may be unsafe.
Secondly, research suggests that when people with PTSD are exposed to trauma reminders that are presented too quickly to be seen consciously (i.e., just a brief flash, or “subliminal” exposure), their DMN responds differently than those without PTSD. A real-life example of this type of subliminal trigger could be, a person walking in a crowded space and not being aware that they’ve glimpsed someone who looks like their former abuser. Even without being consciously aware of this other person, their trauma symptoms may flare.
In one of our studies, after people with PTSD were presented with subliminal trauma triggers, we saw stronger connections between the DMN and a certain brain area called the Periaqueductual Grey (PAG). The PAG plays a key role in triggering our automatic defense behaviours (e.g., fight/flight). These strong connections could help explain the intense fear reactions experienced by people with PTSD, even when they’re not aware of what the specific trigger was - the trigger may have been subliminal.
A third difference we summarize in this paper involves the idea that people with PTSD often feel like their traumatic experiences have become linked to their sense of self. It may be that the trauma has negatively affected how they think and feel about themselves (e.g., I’m bad, just like my traumatic experiences), or that it has interrupted the development of their sense of self (e.g., I don’t know who I am). Review of previous research suggests that this impact on the sense of self may be related to the effect of trauma on the DMN. Perhaps the weaker connections in this brain area (as mentioned earlier) interfere with feeling or developing a sense of self.
Finally, we reflect on the observation that threat/danger seems to increase activity in the DMN. Knowing that this brain area plays a role in experiencing a sense of self, it’s interesting to consider that many people with PTSD are drawn to dangerous behaviours (e.g., driving too fast, walking alone at night in unsafe areas). We wonder if the threat created by the dangerous behaviour (and the increased brain activity in the DMN) might help these people, for a brief moment, feel a stronger sense of self, or have the feeling of “being alive”. Of course, while this may feel good in the moment, there is a serious downside to engaging in risky behaviour - it may lead to getting hurt/more trauma.
This problem emphasizes the need for more research regarding the risky behaviour often seen in people with PTSD. The goal would be to find safe and effective ways to help these patients build or restore a lasting sense of self.
How is the innate alarm system different in people with PTSD?
Terpou BA, Densmore M, Théberge J, Thome J, Frewen P, McKinnon MC, & Lanius RA. (2019). The threatful self: Midbrain functional connectivity to cortical midline and parietal regions during subliminal trauma-related processing in PTSD. Chronic Stress, Volume 3: 1–12.
The innate alarm system (IAS) refers to a network of brain structures found deep within the brain, designed to help us respond to danger quickly. It does so by using a sort of “short cut” within the brain, but the cost of its speed is a loss of detail in the danger message. In fact, our response can be so fast we may not even know what we’re responding to - the message may have been sent subliminally (i.e., below our conscious awareness). In PTSD, the IAS seems to become over-active, often resulting in the person sensing danger or feeling on-guard, even when no real danger exists (i.e., hypervigilance).
One of the brain structures involved in the IAS is the periaqueductal gray (PAG), which is found deep within the brain in an area referred to as the midbrain. From previous research we know that the PAG’s function becomes altered with PTSD. Not only does it tend to become over-active when danger is present, it is over-active when the person is at rest (in the absence of danger), as well. We also know that connections within a specific brain network used for thinking about oneself and one’s experiences (i.e., the Default Mode Network, or DMN) are different in individuals with PTSD. These differences may play a role in changes to how someone perceives their body, the information coming from their senses (e.g., vision, touch), and their emotional experiences. Knowing these differences, our research team wanted to start clarifying how the PAG might be involved in subliminal threat detection – i.e., how dangers that are below our awareness are processed by the brain.
For this study, we recruited two groups of participants – adults diagnosed with PTSD, and adults with no history of mental health diagnoses (the “control” group). While inside an fMRI (functional magnetic resonance imaging) brain scanner, participants were shown personally traumatic or stressful words projected onto a screen, such as “assault”, or “exam”; however, these words were presented so quickly, participants could not have seen them with their conscious mind – they were presented “subliminally”. Our goal was to identify how participants in our PTSD group processed these distressing words in comparison to our “control” group – any differences could help us understand some of the specific effects of PTSD.
Results showed that participants in the PTSD group had stronger connections between the PAG and the default mode network than the “control” group – and again, this was true even though none of our participants were aware of seeing the trigger words. Further, these stronger connections were associated with participants experiencing certain PTSD symptoms – e.g., higher levels of avoidance and dissociation. These results help us understand, more specifically, how PTSD impacts brain function. Knowing these impacts, physicians and therapists can better tailor treatments to an individual patient’s needs and symptoms.
