EASY-TO-UNDERSTAND SUMMARY:
HOW WE PERCEIVE OUR INTERNAL AND EXTERNAL WORLD IN THE AFTERMATH OF TRAUMA
The information we receive from our senses helps us understand, interpret and navigate the world around us. We all know about the 5 senses – sight, sound, smell, touch and taste – but many people do not realize we also receive sensory information from our organs (e.g., the feeling of hunger, thirst, or your heart beating fast). This type of sensory information is called interoception. In general, sensory information helps keep us safe – e.g., we see the wall, so we try to avoid walking into it; we hear a car approaching, so we hurry across the street; or we feel hunger so we eat.
The following research explores how trauma, especially repeated, childhood trauma, can impact our sensory perceptions. As you can imagine, if we sense (or perceive), the world differently, we might behave differently - which can impact our safety. We’re interested in learning about any such changes or differences.
How do brain changes after trauma affect how people with PTSD sense their bodies and the world?
Harricharan S, McKinnon MC & Lanius RA. (2021). How Processing of Sensory Information From the Internal and External Worlds Shape the Perception and Engagement with the World in the Aftermath of Trauma: Implications for PTSD. Front. Neurosci. 15:625490. doi: 10.3389/fnins.2021.625490
In this paper, we review brain changes that could help explain differences in how people with PTSD sense their bodies and the world around them. Sensory information comes from both the outside world (e.g., touch, sound, vision), and from inside the body (e.g., sensations from the gut - like nausea, hunger, and physical sensations that are part of emotion). Being able to process both types of sensory information helps us respond appropriately to the situation we’re in.
In this paper, we review certain theories, including one about sensory sensitivity – how some people may be more sensitive to sensory input than others (e.g., sensitive to sounds and smells). Interestingly, trauma may play a role in this change in sensitivity, for example, causing someone to feel extra alert to sounds/potential danger; or, in the other direction, causing someone to feel numb/shut off.
We also review how brain areas affected by PTSD might overlap with brain areas that process sensory information, perhaps explaining such sensory changes. Further, we suggest these changes may, in turn, affect more complex brain functions (e.g., emotion regulation, certain social skills, working toward a goal). Since brain/sensory changes may alter a person’s perception of their bodies and the world, it makes sense that that this could impact both their ability to regulate their emotions, and their behaviour. An example of this might be when someone feels afraid and takes cover after hearing a loud noise, even though they know it was just fireworks – their brain has sensed danger, and they’ve reacted accordingly.
Further, we describe how a particular brain area, called the insula, seems to play an important role in connecting basic sensory information to complex brain functions. One of our conclusions is that finding treatments to help repair connections to the insula may be helpful in reducing the emotional impact of PTSD. In closing, we emphasize the importance of understanding the impact of trauma on the lower-level brain functions involved in sensory processing when treating PTSD.
Sensory Processing: The Rubber Hand Illusion
The rubber hand illusion (RHI) is a procedure in which the average person can start “feeling” as if a rubber hand has become part of their own body. This illusion involves a participant resting both forearms on a table in front of them, with one arm a little more off to the side. The arm off to the side is then blocked from the person’s view using a box or divider. In place of where their arm would naturally sit on the table directly in front of them, a rubber forearm is placed. Then, to hide where the rubber arm would connect, if it were real, with the rest of their body, a sheet is draped over the person’s shoulders, hiding the connection location (see illustration). Using this setup, the RHI continues with the experimenter brushing the fingers on both the rubber hand and the real, hidden hand (both at the same time) with a soft paintbrush. With the combination of seeing the rubber hand being brushed, and feeling their real hand being brushed, people often start “feeling” as if the rubber hand is their real hand.
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In the past, the RHI has been used to investigate changes in how someone connects with, or feels ownership over, their own body. It had never been studied in participants with trauma-related disorders, such as PTSD. Below, you can read about our early investigations using the RHI in people with trauma-related disorders.
Does the Rubber Hand Illusion have the same effects in people with the dissociative subtype of PTSD?
Rabellino D, Harricharan S, Frewen PA, Burin D, McKinnon MC, and Lanius RA. (2016). ‘‘I can’t tell whether it’s my hand’’: a pilot study of the neurophenomenology of body representation during the rubber hand illusion in trauma-related disorders. European Journal of Psychotraumatology 2016, 7: 32918 - http://dx.doi.org/10.3402/ejpt.v7.32918
Knowing that early traumatic experiences seem to play a key role in the development of dissociative symptoms (e.g., feeling disconnected from oneself, or one’s surroundings seeming “off”), we wondered how people with PTSD that stems from early childhood trauma would respond to the Rubber Hand Illusion (RHI – see description, above).
To begin investigating, we recruited 3 participants diagnosed with the dissociative subtype of PTSD. With each of them, we completed the RHI while recording their behaviour, and certain physical reactions (e.g., heart rate, sweat gland activity). We also asked our participants to complete questionnaires about their experiences with this illusion. To the standard RHI procedure, we included one slight variation - we either brushed the real and rubber hands at the same time (creating that paired experience of seeing and feeling the brushing), or we brushed the rubber hand, then the real hand (i.e., not together, but one after the other). This second approach resulted in our participants’ senses not being in sync – they’d first see the brushing, then feel it a few seconds later. We wondered how these two approaches might impact the RHI in our participants.
As is typical, the rubber hand felt most real to our participants when the brushing of the real and rubber hands took place at the same time. However, we observed strong effects even with alternate hand-brushing (i.e., brushing the rubber hand then the real hand). What’s interesting, is that this is not typically seen in the healthy population. For each participant, both types of brushing caused some distress (e.g., anxiety, unease), derealization (i.e., “I’m having trouble figuring our what’s real and what’s not), and depersonalization (e.g., “I can’t tell whether it’s my hand or someone else’s”, “I can’t tell which hand is which”).
In two participants, the illusion of the rubber hand feeling real led to some freezing/feeling unable to move, as well as traumatic flashbacks. Interestingly, just the sight of the rubber hand was enough to cause some of these effects. In terms of their physical reactions, our participants showed an increase in sympathetic nervous system activity (i.e., the part of the nervous system that helps with the fight/flight response), and a decrease in parasympathetic activity (i.e., the part that helps us relax, “rest & digest”), which echoed their other responses.
These results suggest that the way in which the RHI works may be much more complex in traumatized people than in healthy participants. Further, these results support the idea that the mind-body connection is more easily disrupted in the traumatized population. These preliminary results suggest that the Rubber Hand Illusion could be a promising way to learn more about depersonalization and derealization.
How does the brain's processing of sensory information contribute to trauma-related symptoms, and how can treatment that incorporates sensory processing help?
Kearney BE, Lanius RA (2022). The brain-body disconnect: A somatic sensory basis for trauma-related disorders. Front Neurosci. 2022 Nov 21;16:1015749. doi: 10.3389/fnins.2022.1015749. PMID: 36478879; PMCID: PMC9720153.
The overall goal of this paper is to offer a neuroscience-informed perspective of how somatic (body-based) sensory processing plays a crucial role in how the brain processes trauma and contributes to trauma-related symptoms. We propose that trauma-related symptoms are a result of brainstem-level dysfunction of somatic sensory processing. This dysfunction has cascading effects that lead to difficulty modulating one’s alertness levels, emotions and cognitive functions after trauma. We then offer a rationale of how integrating somatic sensory processing into therapy could improve therapy outcomes.
First, we provide an overview of the vestibular and somatic sensory systems. The vestibular system is composed of parts of the inner ear that inform us about how our head is moving in 3D space. The vestibular system is always working subconsciously until we unexpectedly trip or speed up, which causes the body to react with nervous system arousal. Anyone who has lost their balance knows that feeling - a quickened heart rate, dropping sensation in your gut, and gasping. This response helps keep us physically safe. Therefore, vestibular processing is closely connected with a sense of security, grounding, and safety.
The vestibular system also contributes to body awareness, spatial processing/memory, arousal modulation, first-person perspective, and social cognition, which are all important to consider in trauma. Interestingly, vestibular input has also been shown to help quiet peoples’ minds, enhance body awareness, contribute to emotional regulation, affect nervous system arousal, social cognition, and maintain a coherent sense of one’s body. The vestibular system plays a role in controlling how we process information that we take in from our environment. The vestibular system system may be faulty in PTSD, which could contribute to people with PTSD being hypersensitive or hyposensitive to stimuli in their environments, and could also result in people feeling disconnected from their bodies, which is common when people experience dissociation.
The somatosensory system consists of the skin, muscles, and joints, which detect light touch, deep pressure, pain, temperature, and proprioceptive input (our sense of body awareness). The somatosensory system provides awareness of both signals coming from the environment and signals coming from inside one’s body. Therefore, this system is important in how people with PTSD might lack awareness or be hypervigilant of sensations in their body and their surroundings.
People are born with a desire to seek closeness and care from an attachment figure to meet the child’s emotional and physical needs. This is the attachment system, and when people develop secure attachment, it provides them with a sense of security, safety and acceptance. Children who experience trauma, abuse or have emotionally absent parents often do not develop secure attachment patterns. In a secure attachment relationship, an infant is supported by an attuned caregiver through somatic sensory experiences such as rocking, swaddling and bodily contact. This shows that somatic sensory experiences are important for people to develop secure attachment as children and the ability to self-soothe and feel calm. It is suggested that when people develop insecure attachment as children, it could result in them having dissociative responses in adulthood.
So how does the brain process this sensory information? Lower levels of the brain, such as the brainstem and midbrain, integrate sensory information from inside our bodies and from our environments. Specifically, the periaqueductal gray (PAG) area in the midbrain relays sensory information to the rest of the brain and integrates sensory information with the context and emotional charge of the situation, such as if someone feels fear at the same time. This brain area then coordinates whether your brain perceives that the environment or another person is safe or threatening. Therefore, vestibular and somatosensory information from our body and our environment help our brain determine whether we are safe or in danger. People with classic PTSD and the dissociative subtype of PTSD show differences in the PAG region of their brain on brain scans. The ability to register sensory information and integrate it with information about whether it is safe or dangerous is crucial for regulating nervous system hypervigilance, muscle tone, and posture, all of which are altered in people who have experienced trauma.
When we experience a traumatic event, it not only creates an emotional experience, but it’s also an assault on the senses that reaches lower parts of the brain, like the brainstem. When there is a lot of incoming sensory information during trauma, the brainstem interacts with information about the experience in the PAG to create an overwhelming, aversive experience. After trauma, one’s brainstem can remain “hyperactivated”, which can lead to prolonged disruptions where one “feels too much”. This is common in people with classic PTSD, where they struggle to regulate their emotions, resulting in aggression, emotional/physical overwhelm, and being easily startled. These changes in the brainstem can also contribute to one feeling detached from their body’s sensations and emotions, as is the case in people with the dissociative subtype of PTSD. Interestingly, when people have a history of secure attachment, these parts of the brain have better connections and this protects against long-term impacts of a traumatic event.
In this paper, we provide a model of how somatosensory information is received in the brain, through the PAG, where it is then integrated with other information, and this information travels to other parts of the brain involved in reflection and autobiographical memory. This process ultimately provides people with a sense of self and helps people feel a sense of control and agency. Input from the somatosensory system is even important for infants to develop a sense of self and a sense of agency over their bodies. When this process is disrupted in people with a history of trauma, it can lead to dissociation and feeling disconnected from one’s body.
Therefore, since from a neuroscience perspective, somatosensory input directly impacts nervous system arousal and gives rise to a sense of self, somatosensory awareness can be used during therapy to improve outcomes. The most common treatment for PTSD is cognitive behavioural therapy, but some studies have reported that it has lower than 50% efficacy in PTSD patients, and it can be less beneficial during states of stress or dissociation. There is a big difference between knowing that you’re safe on a cognitive level and actually feeling safe in your body. Therapies that involve reconnecting with a felt sense of safe sensations and movement in the body could be combined with cognitive behavioural therapies. Using somatic sensory awareness could help restore one’s mind-body connection and help people more fully process their trauma and feel alive again.
