Stephen Porges is professor of psychiatry at the University of North Carolina and “Distinguished University Scientist” at Indiana University, where he has created the Traumatic Stress Research Consortium. He is best known for developing polyvagal theory, which describes how visceral experiences affect the nervous system and our resulting behaviour. On Monday 10 June, he will be giving a talk at Love vs Trauma, the Body & Soul charity’s day-long symposium in London, which aims to tackle issues surrounding childhood adversity and trauma. Other participants include Peter Fonagy and Lemn Sissay.

Can you explain polyvagal theory in layperson’s terms?

Polyvagal theory articulates three different branches of the autonomic nervous system that evolved from very primitive vertebrates to mammals. And it’s quite interesting how the sequence evolved. First, you have a system that is really an ancient one, which is death feigning or immobilisation. Then it has a fight or flight system, a mobilisation system. Then finally, with mammals, you have what I call a social engagement system, which can detect features of safety and actually communicate them to another. When you trigger feelings of safety, the autonomic nervous system can help health restoration. In terms of dealing with a life threat, you most likely go into this feigning death, dissociative state.

We hear a lot about fight or flight instincts but less about immobilisation. But is that in fact the most common response to traumatic experiences?

Yes, immobilisation is the critical point of the experience of life-threat trauma events. It used to be assumed by trauma therapists that stress was a fight-flight reaction. But that’s not what the survivors of trauma described. They were describing this inability to move, the numbness of the body and functionally disappearing. And that’s what polyvagal theory described. So when I started giving talks in the trauma world, the theory had tremendous traction because the survivors of trauma said: “This is what I experienced.” And they had been confronted with a world that said: “That’s not what you experienced; why didn’t you fight?”

Society praises fight, accepts flight, but tends to attach shame to immobilisation. Is that fair to say?

The most important word there is “shame”. Survivors are shamed and blamed because they didn’t mobilise, fight and make an effort. That’s a misunderstanding. It’s a poorly informed explanation because the body goes into that state and they can’t move. The theory had traction because it gave survivors feelings of validation. Survival was really an expression of the heroic nature of our body in trying to save us. Sometimes it goes into a state in which we can’t move, but the objective is to raise our pain thresholds and to make us appear to be less viable to the predator. Within the legal system, there’s been a lot of issues when a person hasn’t fought off a predator. And I think this is being poorly informed about how bodies respond.

What is the long-term impact of adverse childhood experiences (Aces)?

Aces is a scale that accumulates exposure to adverse experiences, such as abuse, neglect and family dysfunction. The Aces scale was derived from Dr Vincent Felitti’s observations as a physician in the United States. As he learned more about his patients’ early life experiences, he started to see relationships between early experiences of abuse and long-term health. Research confirmed that higher Ace scores (exposure to a greater number of adverse experiences) were related to longevity and virtually every major medical disorder including heart disease, stroke, Alzheimer’s, cancer and diabetes. More recent evaluations have linked Aces to increased risk for suicide, addiction and psychiatric disorders ranging from attention deficit disorder to psychoses.

We’re not machines detached from our thoughts and feelings. Cats drop dead at the vet’s because of fear and uncertainty

So it’s these adverse events that determine diminished wellbeing?

We have to reframe the question and ask not about the event, but focus on the individual reaction or response. Much of our society defines trauma by the event when the real critical issue is the individual’s reaction. By not accepting that, we end up saying: “If I can survive this and do well, why can’t you?” So we start blaming the survivors again. The point that we have to understand is that when a person has a reaction or response to trauma, the body interprets the traumatic event as a life threat. There’s a massive retuning of how the nervous system works, how it regulates underlying physiological systems that impact social behaviour, psychological experiences, and also on physical outcomes.

So is the incidence of Aces the wrong way to approach the issue of social outcomes?

No, it’s a very important initial acknowledgment of what is happening in the lives of many, many individuals. But the acknowledgment of that is just the beginning. Because we have to understand that people respond differently to the same physical challenges. And by just looking at Aces, we’re missing many individuals who are having adverse reactions to events that we may think as being relatively minor. For example, we see the overlap between medical procedures that are not welcomed, like emergency surgery, and the consequences of rape. You’re dealing with similar parts of the body and the body can see both cases as an unwelcome intrusion. Now the Aces model wouldn’t pick up the surgery, but Aces is still a very important and powerful first step.

You emphasise the importance of safe spaces for the traumatised. How can these be applied?

Whether we’re talking about medical treatment or psychiatric models, the context in which the treatment is delivered becomes important, because the context triggers cues in the nervous system, which will make it either defensive or available to treatment. So the first thing is to understand how bodies respond to context. A scared individual doesn’t bring into an operating arena a nervous system that is going to cooperate and collaborate with the medical procedures. We’re not machines that are detached from our thoughts and feelings. In veterinary medicine, animals like cats often drop dead within the veterinarian’s office because of the fear and uncertainty. So we’re working on ways of giving cues of safety.

Polyvagal theory has made inroads into medical and psychotherapeutic treatment, but how should it inform how people treat each other?

When we become a polyvagal-informed society, we’re functionally capable of listening to and witnessing other people’s experiences, we don’t evaluate them. Listening is part of co-regulation: we become connected to others and this is what I call our biological imperative. So when you become polyvagal-informed you have a better understanding of your evolutionary heritage as a mammal. We become aware of how our physiological state is manifested, in people’s voices and in their facial expression, posture and basic muscle tone. If there’s exuberance coming from the upper part of a person’s face, and their voice has intonation modulation or what’s called prosody, we become attracted to the person. We like to talk to them – it’s part of our co-regulation.

So when we become polyvagal-informed, we start understanding not only the other person’s response but also our responsibility to smile and have inflection in our voice, to help the person we’re talking to help their body feel safe.

• Love vs Trauma: The Frontiers of Healing Childhood Trauma – A Symposium is at the Barbican Centre, London EC2, on Monday 10 June. Tickets cost £187.14-£229.78 and are available from Eventbrite