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The polyvagal theory, autism, and PTSD

ECG Ventricular TachyCardia

As we discussed above, Panksepp notes that FEAR neurocircuitry projects to "autonomic and behavioral output components of the lower brain stem and spinal cord." As we discussed in Part 1 of, the vagus nerve is part of the autonomic nervous system and arises from the lower brainstem, specifically the medulla, and innervates the viscera—the internal organs of the body including the lungs, heart, liver, and intestine—with autonomic sensory and motor fibers.

In an interview with Ravi Dykema of Nexus: Colorado's Healthy-Living Connection, March/April 2006, Stephen W. Porges, Professor and Director of the Brain-Body Center in the College of Medicine at the University of Illinois at Chicago, explains that the vagus nerve—the primary nerve for the parasympathetic nervous system—has two major branches: an ancient unmyelinated branch that we share with reptiles and a more recently evolved myelinated branch unique to mammals that "is linked to the cranial nerves that control facial expression and vocalization."

Porges's polyvagal theory proposes an automatic-response hierarchy emphasizing that when mammals detect they are in a safe environment, their bodies automatically activate the more recently developed myelinated branch of the vagus nerve that promotes "calm states, to self-soothe and to engage." What Porges calls the social engagement system determines the quality of interpersonal exchanges, regulating "the features that we show other people, the facial expression, the intonation of our voice, the head nods, even the hand movements…."

House Party

Porges points out that "when we're stressed or anxious, we use our facial muscles, which include the ears. We eat or drink, we listen to music, and we talk to people to calm down." He emphasizes: "We forget that listening is actually a 'motor' act and involves tensing muscles in the middle ear. The middle ear muscles are regulated by the facial nerve, a nerve that also regulates eyelid lifting. When you are interested in what someone is saying, you lift your eyelids and simultaneously your middle ear muscles tense. Now you are prepared to hear their voice, even in noisy environments."

When circumstances change and one detects danger, Porges explains that our automatic defense system employs either "the sympathetic-adrenal system to mobilize for fight and flight behaviors," or, when circumstances are perceived to be so dire that fight or flight is useless, the ancient unmyelinated vagal system immobilizes us, just like an animal freezes when escape from a predator is impossible.

crocolydus acutus

In a 2010 interview with Lauren Culp of the Global Association for Interpersonal Neurobiology Studies (GAINS), Porges says: "By not moving, the mammal would not be detected by [the] predator and, as a byproduct of this strategy, consciousness might be lost or for humans states of dissociation may occur." In "The Polyvagal Theory for Treating Trauma," a National Institute for the Clinical Application of Behavioral medicine (nicabm) teleseminar, Porges explains that "If a life threat triggers a biobehavioral response that puts a human into this state, it may be very difficult to reorganize to become 'normal ' again."

To put Porges's polyvagal theory in more academic terms, a chapter that Porges authored in The Integrative Neurobiology of Affiliation, edited by Carol Sue Carter, I. Iza Lederhendler, and Brian Kirkpatrick (Massachusetts Institute of Technology, 1999). When the more recently evolved myelinated vagal system is active (what Porges identifies as the VVC—ventral vagal complex), we have "the ability to communicate via facial expressions, vocalizations, and gestures." When this system is inactive, "the sympathetic nervous system is unopposed and easily expressed to support mobilization such as fight or flight behaviors." In terrifying circumstances, when the ancient unmyelinated vagal system (what Porges identifies as the DVC—dorsal ventral complex) kicks in, "immobilization and potentially life-threatening bradycardia [slowed heart action], apnea, and cardiac arrhythmias occur." Porges explains that such immobilization is "the vestige from the reptilian vagal control of the heart and lung. In contrast to reptiles, mammals have a great demand for oxygen and are vulnerable to any depletion in oxygen resources. The metabolic demand for mammals is approximately five times greater than that for reptiles of equivalent body weight. Thus, reptilian dependence on this system provides a shutdown of metabolic activity to conserve resources during diving or death feigning."

In the Nexus interview, Porges reminds us that people suffering from PTSD, autism, panic disorder, or any other hypervigilant state are unconscious of the neurobiological process behind their symptoms, which are, Porges explains, an "adaptation to a situation" that his/her nervous system has "evaluated as dangerous." He points out that strategies to reason with or negotiate with a patient frequently do not work to improve engagement and interaction with others. Porges says "to make people calmer, we talk to them softly, modulate our voices and tones to trigger listening behaviors, and ensure that the individual is in a quieter environment in which there are no loud background noises."

Porges notes in the GAINS interview: "At least 60% of individuals with autism have auditory hypersensitivities." In working and interacting with individuals, he emphasizes the importance of "respecting the physiological state of the other and respecting the sensory world of the other person…." In working with trauma victims, Porges advises therapists to encourage their clients to "celebrate the success of their bodies in navigating and negotiating extraordinary dangerous situations" and respect "how their body and their nervous system put them in a state in which they could survive."

In dealing with stress, Porges recommends to everyone to remember what it is to be a human. He tells Nexus readers: "Part of being a human is to be dependent upon another human. Not all the time, of course. Similar to most mammals, we come into the world with great dependence on our caregivers, and that need to connect and be connected to others remains throughout our lives." He emphasizes the need to create safe environments for ourselves in which we can socially engage.

Fear processing, PTSD, and kindling:

A March 2009 report from the Society for Neuroscience, "Post Traumatic Stress Disorder," aligns with Amy F.T. Arnsten's ideas about how stress can produce impairments in the prefrontal cortex (see Stress, attention, learning, memory, and ADHD). The Society for Neuroscience reports: "Patients with PTSD have heightened levels of norepinephrine, a chemical involved in arousal and stress. High levels of this chemical strengthen the emotional reactions of the amygdala, a brain region involved in the fear response, while weakening the rational functions of the prefrontal cortex, which normally allows us to suppress troubling memories and thoughts."

There is interesting evidence of a mechanism within the human brain that helps suppress troubling memories and thoughts in a way that is healing. In Animals in Translation, Grandin and Johnson draw attention to Ruth Lanius et al., "The Nature of Traumatic Memories: A 4-T fMRI Functional Connectivity Analysis." During the study, brain scans were conducted for eleven people with PTSD as a result of sexual abuse, assault, or car crashes as well as for thirteen people who had suffered the similar experiences without developing PTSD. Those who suffered from PTSD remembered their trauma visually, more like a flashback, while those without PTSD remembered their trauma as a verbal narrative. In a summary of this research, titled "Brain Activation May Explain PTSD Flashbacks," Joan Arehart-Treichel quotes Bessel van der Kolk, M.D., a professor of psychiatry at Boston University and medical director of the Trauma Center there.

Dr. Lanius has elegantly demonstrated how people's brain function differs when they are in dissociate states.… We always suspected that when people go into these states, there is a decrease in activation of the left inferior prefrontal cortex—meaning that people are less capable of taking in new information and being curious about the world out there—and that the brain shifts to a more right posterior activation—more to a state of fear and flight.”


If language helps humans suppress fear, it is easier to understand why animals do not possess the same ability to suppress fear as people do. Grandin, who has made a career working with animals, asserts: "I do know that once an animal has become traumatized it's impossible to un-traumatize him. Animals never unlearn a bad fear." Grandin and Johnson point out that animals are aware of tiny details in their environments and can become afraid of these tiny details. The authors describe this as "hyper-specific" fear. "It comes from autism research, because autistic people are extremely hyper-specific. You see the trees better than the forest. A lot of times you might not see the forest at all. Just trees, trees, and more trees." The authors point out that animals will react fearfully to any stimulus that resembles, in terms of sensory perception, an initial fearful experience. They describe a dog's encounter with a red hot-air balloon which severely frightened the animal. Subsequently, the dog reacted fearfully to any red, circular object, even the read aerial markers that draw attention to power lines.

In Affective Neuroscience, Jaak Panksepp notes that PTSD is "characterized by permanent personality changes, including frequent moods of intense fear and anger." The Society for Neuroscience reports that PTSD symptoms may "include intrusive memories, emotional numbness, and insomnia."

In Part 1 of, we discuss kindling (see Kindling and stress—how experience affects the brain). In our discussion of FEAR neurocircuitry here, Panksepp explains in more specific detail the experimental procedure known as kindling in which "animals are induced to exhibit epileptic states by the periodic application of localized electrical stimulation to specific areas of the brain." Panksepp points out that the "amygdala, an emotion-mediating brain area, is an ideal site for kindling studies, since seizure activity can be induced here most rapidly." Citing a wide range of research studies, Panksepp succinctly describes the kindling procedure:

The procedure consists simply of applying a burst of brain stimulation through indwelling electrodes for a period of one second, once a day, for a week or two. After the first brief ESB [electrical stimulation to the brain], nothing special happens, unless one observes the EEG, where one will note a momentary seizure immediately after the brain stimulation. This induced epileptic fit gets larger and larger as the days pass, and after a few days, the ESB begins to provoke brief periods of outright convulsive activity. After a week or so, the brief stimulation produces a full-blown motor fit, unambiguous both behaviorally and in the poststimulation EEG. Thereafter, the animal will always have a seizure when it receives this burst of brain stimulation. Gradually even other stimuli become capable of triggering seizures, especially loud sounds and flashing lights.

Giving animals seizure-inducing drugs every several days or even exposing them to very loud auditory stimulation also induces kindling, sometimes provoking fits in certain sensitive strains of animals. The induction of these epileptic states reflects a functional reorganization of the nervous system, since no structural changes have been found to result from kindling procedures.

Panksepp observes that "the emotional personality of these animals seems to change as they become kindled. Cats tend to become temperamental and irritable. In female rats, we have observed a form of 'nymphomania'." Panksepp says that normal female rats are sexually receptive "for only a couple of hours every four days, but after kindling many females remain in constant estrus. They are willing to have sex with males at all times. It is as if their hormonal receptivity cycle has been locked in overdrive."

"The severity of PTSD can be diminished with antiseizure medications, such as carbamazepine," notes Panksepp. He points out that carbamazepine facilitates the inhibitory activity of gamma-aminobutyric acid (GABA) and blocks the effects of previous kindling. In Part 3 of, regarding obsessions and compulsions, we also discuss the inhibitory neurotransmitter GABA along with the nucleus accumbens, which is intricately connected with the easily kindled amygdala.

Fear, autism, splitting, and savantry:

As you may know, Temple Grandin is autistic and has made a career working with animals, especially in improving conditions for farm animals raised for food. She writes: "This is what I have in common with animals. Our fear system is 'turned on' in a way a normal person's is not. … If I hadn't gone on medication I couldn't have had a life at all. I certainly wouldn't have been able to have a career."

In Animals in Translation, Grandin and Johnson write: "It seems likely that animals and autistic people both have hyper-fear systems in large part because their frontal lobes are less powerful compared to the frontal lobes in typical folks. The prefrontal cortex gives humans some freedom of action in life, including some freedom from fear. As a rule, normal people have more power to suppress fear, and to make decisions in the face of fear, than animals or (most) autistic people."

brain anatomy amygdala

Regarding the frontal lobes, Grandin and Johnson write: "The frontal lobes fight fear in two ways. First, the frontal lobes are the brakes. The frontal lobes tamp down the [action of the] amygdala …. The amygdala tells the pituitary to pump out stress hormones such as cortisol; the prefrontal cortex tells the pituitary to slow down." The position of the amygdalae within the temporal lobes can be seen in the MRI to the right (image links to NIH source). The MRI shows fMRI activation of the amygdalae highlighted in red.

Grandin and Johnson point to a core difference between animals and autistic people on the one hand, and normal people on the other. "Animals and autistic people are splitters. They see the differences between things more than the similarities. In practice this means animals don't generalize very well."

Regarding savantry, Grandin and Johnson point to the research of Allen Snyder and D. John Mitchell who propose that "all the different autistic savant abilities come from the fact that autistic people don't process what they see and hear into unified wholes, or concepts, rapidly the way normal people do." Grandin and Johnson explain that a normal person doesn't become conscious of what he's looking at until after his brain has composed the sensory bits and pieces into wholes. The authors point out that an autistic savant is conscious of the bits and pieces. They note Snyder's and Mitchell's conclusion that "the reason autistic people see the pieces of things is that they have privileged access to lower levels of raw information." Snyder's article, "Explaining and Inducing Savant Skills: Privileged Access to Lower Level, Less-Processed Information," is available on the web.

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