This article seeks to convey pragmatic and applicable knowledge of the human nervous system to people affected by Parkinson’s Disease and those involved in providing healthcare and caregiving, as well as to try to summarize for myself my own current understandings of these concepts. In particular, we explore the role of people, attitudes and relationships in the lived experience of people with PD.
Neuroception and the Nervous System
The human Nervous Systems constantly evaluates whether the current situation and environment is safe or dangerous. The biological mechanism of scanning the environment for signs and portents of safety versus danger/threat, and for making snap decisions based on these, is via a fast subconscious process known as "neuroception". Physiological shifts then occur according to the neuroceptive evaluation, and these physiological responses include three fundamental outcomes, as well as admixtures of these.
Upon evaluation that the current environment is safe, the body is able to relax, the mind to quieten, and the whole able to be in connection with other people in healthy and restorative, socially engaged ways. This state of safety is mediated by the activation of a group of important cranial nerves that are connected to the muscles of the face, neck, lungs and heart, and which form part of the Parasympathetic Nervous System.
However, when a threat is subsequently detected, then a shift in physiology occurs, which prepares the body for mobilized defensive behaviours, e.g. to fight or flee, via activation of the Sympathetic Nervous System. When so mobilized for defence, the bodily functions required for safe connection with other people are downgraded, so we become socially disengaged, less empathic and more selfish.
When neuroception deems mobilization is not enough to escape the danger, another shift in physiology occurs and we shutdown, freeze, play dead or otherwise immobilize. This occurs through activation of another part of the Parasympathetic Nervous system called the dorsal or sub-diaphragmatic Vagus Nerve. In this shutdown state, all but the most fundamental systems required for survival are significantly downgraded, especially those of healthy social interactions, and this continues until our neuroception deems the danger has passed.
Neuroception gathers its input from many of other senses in order to make its evaluation, including detecting movement, sounds, smells, touch, imminent falls or trips, and so forth, as well as taking in information from various parts of the Nervous System, including the "second brain" of the enteric Nervous System, from which gut instincts arise, and also accounting for emotions and feelings that generated, in part, from the "third brain"-like neuronal clustering of the heart.
Social and Safe
Neuroception also accounts for who else is present, for example whether we are alone in a potentially dangerous situation, or whether we are supported by others who can help render, perhaps through protection, collaboration, or safety in numbers, the situation less dangerous. Importantly, our neuroception reads and interprets the neuroceptive processes of other people, via the state of their Nervous System through facial expressions, tones of voice, body language and posture, touch, and I suspect many other subtler signs, e.g. pheromones, electro-magnetic fields, thermal signatures, and more. Thus, when more than one person is involved in a potentially dangerous or threatening situation, the physiological shifts experienced by each individual arise from a subtle interplay of their neuroceptive responses, leading to complex group dynamics.
Since a person with a nervous system that is in safe mode can convey this sense of safety, through positive or empathic facial expression, melodic tone of voice, relaxed posture and stance, and if proximate, re-assuring touch, this can help other peoples neuroception to also decide the situation is safe. This ability of one persons’ nervous system to calm that of another is called "co-regulation". Conversely, if a person is feeling threatened, the externalization of their nervous system state, displayed through angry or fearful facial expression, screaming or shouting, defensive postures and mobilizations, grabbing on to others, can influence the neuroceptive evaluation of other people towards feeling threatened too. In large groups, this can have a domino effect, leading to mass panic.
How much weight the neuroception of one person gives to what it can detect in the state of a specific other is likely influenced by many factors, such as their relationship, family ties, past experience, (im)balances of power, (dis)regard, (dis)respect. So a strong or charismatic leader might be able to influence the neuroception of many other people significantly, a child will react very strongly to the nervous system state of a parent, and a person who is chronically ill’s sense of impending life threat will be significantly influenced by the nervous system state of a doctor during a medical appointment, either through reassuring signs of safety or displays of defensive states.
People and Threat
Neuroception also needs to evaluate whether other people are themselves a source of danger, not only in deciding if a stranger is a threat or is friendly, but also if a familiar person is in a physiological state which is safe to be with. While the threat reaction to a stranger might include autonomic mobilizations or immobilizations similar to those which arise when faced with a dangerous animal, say, neuroception may have a much more intricate and subtle role in threat reduction from a familiar person, especially where there is a significant power imbalance in the relationship and one person is reliant on the other for provision of essential resources, such as food, shelter, money, physical assistance, protection, care, love.
This is the situation in infancy, for example, when a baby is totally reliant on a parent to provide the essential resources for life, and with infirmity in old age, but is also very relevant in healthcare and caregiving of debilitating chronic illness. An existential threat arises for a reliant person if a provider disconnects or withdraws, in which case the essential resources may become unavailable, or there is a danger of becoming isolated or unprotected. Provider withdrawal not only includes the act of physically leaving, but also social disengagement when the provider's own nervous system feels unsafe and shifts to a defensive, and hence more selfish, physiological state, in which the the reliant person's needs become deprioritized.
Neuroception constantly evaluates the provider's face, voice, gestures, touch, etc., for signs of connection or imminent withdrawal. As well as overt signs such as anger or fear, the neuroception of a reliant person is prone to detect a threat of withdrawal or disconnect if it perceives a provider is belittling, blaming, shaming, ignoring or criticizing them. When disengagement is sensed, a stress or threat reduction response may arise, consisting of seeking to influence the provider's neuroception, and hence their physiological state and sense of safety. This involves the reliant person altering their own tone of voice, facial expression, body language and behaviour in order to try to shift the physiology of the provider towards a state which reduces the risk of disconnection, and hence the potential loss of access to resources. As the reliant person masks their own physiological state, emotions and feelings, this is not a true socially engaged state of both people being relaxed and feeling connected, and since it is still a form of stress response, it does not convey the benefits to health, restoration or growth that true social engagement and connectedness does.
Personal and Past
Neuroception and its sensitivity is very person dependent, so a situation which one person finds safe and enjoyable may be evaluated as life-threatening by another person's danger sense. In particular, neuroception is greatly influenced by history and past experience, and can become more sensitive to potential threats as stressful experiences and traumas mount up. Thus the amplitude of danger signs needed to shift someone into a physiological threat response state may get lower over time, while cues of safety get further downgraded, so that the person's neuroception becomes more hypervigilant to danger/threat and errs on the side of threat more easily.
RELEVANCE TO PARKINSON’S DISEASE
I believe that Idiopathic Parkinson's Disease can arise when our neuroception becomes so sensitized to danger that it is constantly evaluating life threat, such that the immobilization stress response becomes stuck on. This nervous system based perspective does provide a simple and elegant explanation for the lived experiences of people with PD, including all motor and non-motor symptoms, see
THE NERVOUS SYSTEM AND PARKINSON'S DISEASE.
Indeed, people with PD can freeze totally, a classic example is getting frozen when moving through a doorway, or when becoming unbalanced. From personal experience, being in this frozen state is very much like being a deer stuck in the headlights of a vehicle. Eyes glaze and become unfocussed, body becomes a rigid statue, speech or communication is very difficult, breathing becomes very shallow, rational thinking stops.
Another animal based metaphor for what its like to have PD, more generally, is that of a very sensitive tortoise/turtle which retreats into the protective shell at the slightest hint of danger. Through this looking glass, anything which puts the person with PD into a defensive state will make them withdrawal more, resulting in worsening symptoms by deepening and prolonging shutdown and rigidifying and thus armouring the body. Conversely, removing sources of apparent threat and developing resources which help make the person feel safer will allow them to poke their heads out the metaphorical protective shell and emerge for longer, thus reducing symptoms. There is much a person with PD can do to help themselves (the other articles on this website contains many ideas of things to try) to become more resilient and spend more time out of their shell, but the role of people and relationships on symptoms and thus quality of life should not be underestimated.
The tortoise imagery is worth recalling whenever interacting with people with PD. As Deb Dana, author of "The Polyvagal Theory in Therapy", says
“to get a turtle to come out of the shell, you don’t knock on its shell and you don’t shake them... You just kinda sit there patiently... But you really have to be beaming that ventral vagal energy to that system.”
In people with PD, the warning signs of withdrawal include:
unfocussed eyes, rarely looking to the horizon or into the distance, sitting with eyes closed a lot, aversion to bright light;
aversion to music, not able to heed what other people are saying, rejection of the advise of others;
loss of sense of smell and no longer appreciating or noticing delicate aromas;
hands empty, fingers curled, toes curled, aversion to physical touch and to touching;
wolfing down food, eating mechanically without really tasting;
loss of connection with the immediate environment - only noticing things when they are very close by;
avoiding the warmth of the sun, but also feeling the cold acutely.
In terms of interpersonal impact factors, anything which makes the nervous system of a person with PD feel threatened or isolated will very likely trigger a withdrawal-further-into-the-shell type response. In particular, trying to motivate or move people with PD through cajoling, nagging, shouting, blaming, shaming, embarrassing, name-calling, belittling, or showing frustration or unkindness in any way, is just not going to work, but instead will trigger their neuroception, resulting in the contrary effect, making them more withdrawn and unmotivated. Those of us with PD can't help this, it is the way our nervous system is configured due to a very sensitive neuroception which easily gets us stuck. Our greatest need is to feel safe, and this does require an awful lot of patience, kindness and a basic understanding of the human nervous system from the people around us.