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Connections Between the Behavioural Immune System and Dissociation
Disgust Reactions as a Bridge Between the Immune and Nervous Systems
In this article, we explore two types of reaction both mediated by the disgust circuits of the brain and body, one of the immune system, namely the Behavioural Immune System, and one of the nervous system, namely traumatic recapitulation of the “flag and faint” or dissociation stress response. We consider how these might interact, via the activation of disgust, and hence form a bridge directly connecting immune and nervous system responses. In particular, we consider the feedback between fear of infection, and dissociative complex PTSD type symptoms.
The Behavioural Immune System
I first came across the concept of the “Behavioural Immune System” (BIS) during the pandemic, via Jarl Clausen’s “Vegetative Training” article on the subject, which was somewhat critical of the pandemic response due to not properly accounting for this psychological aspect of the immune system. However, the BIS has much wider application and relevance to society than just the pandemic, especially, as we will see, for folks suffering from trauma.
According to Mark Schaller’s American Scientific article, the BIS is:
“our [nervous system’s] way of engaging in a kind of preventative medicine, it is a suite of psychological mechanisms designed to detect the presence of disease-causing parasites in our immediate environment, and to respond to those things in ways that help us to avoid contact with them.”
So the danger sense circuits of our nervous system are constantly on the look-out for signs or symptoms of infectious diseases in other people, such as sneezing, coughing, rashes, pustules, or “sickness behaviours” such as exhaustion or irritability. As well as visual cues, we may also pick up on smells and sounds associated with sickness. For a deeper exploration of a myriad of different ways that our own internal states may be affected by cues from other people’s physiology, see:
According to to Schaller:
“it makes immediate sense that people would develop aversions against people who… have infectious diseases.”
This aversion is engendered by the activation of the disgust circuits of the nervous system, and indeed, the pathogen disgust system and the BIS are found to be functionally the same. So the BIS recruits disgust in order to create avoidance behaviours, which protect us from coming into contact with pathogens.
Just like when we encounter rotting matter, or blood, or faeces, when we encounter sick people from outside of our extended family, we also tend to experience revulsion, and move away, or try to get the sick person to move away from us. These are largely autonomic responses, and hence take a great deal of conscious awareness and effort to overcome or disobey.
However, the psychological and physiological components of our immune response are indelibly intertwined. For example, it has been shown if a person detects cues of sickness in another person, immune activity and inflammation markers in the viewer increase. Studies have even shown that just looking at a photo of a visibly ill person, the immune marker interleukin (IL)-6 concentration increases in the viewer.
Indeed, according to Schaller:
“when people experience disgust (the emotion that signals threat of infection), there are increased markers of immunological function in people's saliva, and in an experiment that my colleagues and I published last year in Psychological Science, we found that the mere sight of other people's symptoms of sickness (sneezes, sores, rashes) led perceivers' own white blood cells to respond more aggressively to bacterial infection.”
So when the BIS/disgust systems are activated, these create pro-inflammatory, immunologically active states in the body.
Conversely, the more that infection represents a threat to someone, for example for folks who have a weakened immune system, or who already has a high pathogen/toxin load, or high levels of inflammation, the lower the threshold for activation of the BIS/disgust system. Again from Schaller:
“a woman's immune system is suppressed during the first few weeks of pregnancy, leaving her body more vulnerable to infection… one consequence is that women are more sensitive to sights and smells and tastes that trigger disgust... another consequence is that, compared to women in later stages of pregnancy, women in their first trimester show higher levels of [social aversion].”
The Dissociation Stress Response
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Interestingly, the same disgust system which activate the BIS, also mediates an extreme nervous system response, when someone is proximate or comes into a contact with a potentially lethal threat that they can’t escape, such as being attacked by a predatory animal or by another person. If this results in traumatization, the same stress response can be recapitulated by trauma reminders, and become part of complex PTSD type symptoms.
One of the best articles I ever read on the nervous system’s “defence cascade” that occurs in reaction to our danger senses perceiving a threat, is “Dissociation Following Traumatic Stress: Etiology and Treatment” by Maggie Schauer and Thomas Elbert.
In the article, Schauer & Elbert explain how the nervous system goes through several escalating stages of defence mechanisms in response to a detected threat. This starts with a orienting/startle response, and, if the threat is evaluated as real, escalates to fight or flight responses. Then, if the threat cannot be escaped or fought, the first type of freeze response stage begins.
This is variously known as “tonic immobility”, “fright”, “catatonia”, or “playing dead”, where the body becomes stiff and rigid, and the person is literally “frozen in fear”, “scared stiff”, or “like a statue”. Below is a video showing an opossum in tonic immobility. People with Parkinson’s are stuck in this type of freeze.
However, there is a final stage of the stress response defence cascade, which occurs if the tonic immobilization wasn’t sufficient to remove the danger, and the person is about to come into direct contact with the threat, imminent contamination, bodily invasion, or penetration, e.g. caused by the sight of blood, being bitten by an animal, or stabbed with a knife. This final stage is known as “flag and faint” or “flaccid immobilization”, as it causes the person to collapse as the body goes limp and floppy, and can may ultimately result in unconsciousness. It is this flaccid immobilization stage which is mediated by the disgust system.
The below quotes are according to Schauer & Elbert.
“Threat-induced flaccid immobility up to fainting, a response also seen in blood-injection-injury phobia, could have evolved as a guard against the danger of cardiac failure during inescapable attacks.”
“Fainting seems to be mediated through disgust, which enables emotional responses to potentially infectious or noxious material in advance of actual contact with such material, to avoid pathogens and their toxins or invasive procedures. Across cultures, disgust is universally elicited by disease-salient contacts such as bodily secretions, viscous substances, vermin, and sick or dirty people. Experiencing, witnessing, or listening to situations perceived as ‘‘disgusting’’ (e.g., mucus/stool, suctioning, wounds, colostomies) can trigger [it].”
While fainting may be the ultimate solution of the disgust system, it is a preceded by the person “flagging”, i.e. becoming flaccid, and dissociating from their body. Schauer & Elbert give a vivid description of what experiencing this dissociation is like.
“In contrast to tonic immobility, flaccid immobility has a slow onset and slow termination. Only over the course of several minutes dissociative reactions begin to dominate (an abrupt onset is observable only once the response is conditioned [by trauma]). The muscle stiffening changes to flaccidity, voluntary movements stop, so does speech. Even if there is effort from the survivor, language production fails; the mouth might open, but there is no vocal sound.”
“The central skeletal muscles are flagging, so that the posture subsides. The [person] reports that perception of internal or external stimuli becomes attenuated, sounds and voices become distant, visual stimuli fade or become unreal (derealization). [Bodily and pain] stimuli no longer seem to reach the central processing units, causing changes in body awareness and loss of control (depersonalization). Numbness prevails. Conscious processing of the events becomes limited, making meaning seems irrelevant… emotional involvement fades away, that is, no action dispositions are assembled and memory consolidation becomes weak... It may require minutes to hours for a patient to be oriented in reality.”
The second important point of Schauer & Elbert’s work, is that once someone has experienced a stage of the defence cascade during a traumatization, these states may be later recapitulated due to triggers or cues which remind their nervous system of the traumatic event. For those folks suffering from trauma who experienced the flag and faint stage during traumatic episodes, they may experience some or all of the aspects of the dissociation described above when they are triggered and recapitulate the trauma. This type of dissociation is particularly linked to people who suffer with complex PTSD. Since the original flag and faint episodes were triggered by activation of the disgust system, it is likely that later experiencing of disgust will act as a reminder trigger for dissociation.
Above we have explored the BIS and the dissociative “flag and faint” stage of the nervous systems defence cascade, and how the resulting dissociation may be recapitulated in response to trauma triggers, as both being mediated by the disgust system. It is therefore likely that BIS and dissociation co-activate, and interact, when disgust is triggered, forming a link between the immune and nervous systems.
Since I am not aware of anyone connecting these dots before, it is worth speculating how these two aspects of the disgust system may combine and interact.
When the BIS is activated, and through it the physiological immune system is also activated, due to cues of the presence of an infected person, this likely comes with some level of disgust activated dissociation. Indeed, dissociation may be part of the suite of the psychological mechanisms which form the BIS, that result in the aversion to other people.
Conversely, folks who already experience dissociation due to traumatic recapitulation of flag and faint episodes, the activation of the BIS by perceived presence of an infected person, may be a significant co-trigger of symptoms. People with complex PTSD are therefore likely to be sensitive, and have a lower threshold, to cues of the presence of infection, and this may manifest as increased social withdrawal.
It is also interesting to consider how these interactions may have played out in the extreme case of the pandemic, when the cues and symbols of infection were ever present, and could not be escaped, and when fears of infection were greatly heightened. I may cover this in a sequel, but what I am pondering is whether the extreme activation of BIS/dissociation explains why some people were able to totally ostracize and shun even close family members, and also whether the lack of memory consolidation during dissociation explains why some people are seemingly now unable to remember the extent of what we experienced during the first years of the pandemic.