Goodbye to the polyvagal theory

By , PhD in psychology and therapist in Oregon, United States

What therapist doesn’t love polyvagal theory? Since 2009, when he first publicly shared his theory of how trauma affects the nervous system, it has been widely adopted not only by mental health therapists but also by yoga instructors, meditation teachers, and almost anyone interested in treating trauma. trauma. Polyvagal theory has also been praised by giants in the field of traumatic stress such as Bessel Van Der Kolk, Pat Ogden, and Peter Levine. As a clinical psychologist, I also believed that polyvagal theory offered exciting implications for healing through the nervous system.

What is polyvagal theory?

The polyvagal theory focuses on the , which extends from the brain stem to all internal organs, including the heart, lungs, and stomach. The vagus nerve has many functions, one of which is to be the conduit for the parasympathetic nervous system, which is responsible for stimulating “rest and digest” activities, such as slowing breathing and heart rate, and increasing digestion. The vagus nerve is essential for calming the nervous system, especially after experiencing a stressor.

According to Porges (1995), the three premises of polyvagal theory are (as I paraphrase them for my non-neuroscientist colleagues):

  1. Respiratory sinus arrhythmia (RSA), or changes in heart rate that are typically synchronized with breathing, and neurogenic bradycardia, a sudden and extreme drop in heart rate, are mediated by different branches of the vagus nerve. RSA is regulated by the ventral branch and neurogenic bradycardia by the dorsal branch. These branches can operate independently of each other.
  2. There is a phylogenetic hierarchy of the two main branches of the vagus, the dorsal and the ventral. The dorsal vagus is a vestigial relic of the and is responsible for neurogenic bradycardia.
  3. The ventral vagal branch is a unique mammalian adaptation that allows mammals to detect novelty, actively interact with the environment, and communicate socially. It does this by removing vagal tone, which has the effect of increasing heart rate. Nicknamed the “intelligent vagus” by Porges, the ventral vagus is absent in other vertebrates such as fish, snakes, and birds.
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In other words, if the vagus nerve were like the braking system of a car, the ventral vagus would be the brake pedal, gradually slowing your heart rate. When a person encounters a stressor, the release of the ventral vagal brake allows for an increase in heart rate and possible activation of the “fight or flight” response if necessary.

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On the other hand, the dorsal vagus would be the emergency brake and is responsible for the “freeze response” that appears as a sudden and extreme drop in heart rate, decreased breathing and muscle immobility.

Debunking the polyvagal theory

While the overall function of the vagus nerve is not in dispute, a growing number of scientists point to evidence refuting the polyvagal theory (for an extensive discussion, see Paul Grossman’s (2016) question in ). According to neuroscientific research, it is unlikely that any of the three premises are true.

Regarding premise number 1, neuroscience research has repeatedly found that the dorsal branch of the vagus has little effect on heart rate (Cheng et al., 2002; Cheng et al., 2004; Farmer et al., 2016; Geis & Wurster, 1980; Verberne, 2004). Grossman (2016) has also argued that the evidence Porges has presented in support of the effects of the dorsal vagus on neurogenic bradycardia is sparse and flawed.

Regarding premises number 2 and 3, many studies have found evidence that the ventral vagus exists among lizards and fish. Therefore, it is not an exclusively mammalian adaptation as Porges claims (e.g., Barbas-Henry, 1984; Campbell et al., 2006; Grossman & Taylor, 2007; Monteiro et al., 2018; Taylor et al. , 2010; Taylor et al., 2006; al., 2014).

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I feel a little like the Grinch who stole Christmas for saying this, but we have to stop teaching polyvagal theory to our clients and students. Sometimes a theory doesn’t work even though it sounds cool; that’s science.

Can anything be saved from the polyvagal theory?

Shin Shin Tang. Image Description: A black ink drawing of a headstone that says “RIP Polyvagal Theory (1994-2021) with a heart on top and some flowers at the base.

In light of the evidence, I don’t think so. However, there are many aspects of the trauma response that are still real phenomena, such as neurogenic bradycardia and the traumatic freezing response. They simply cannot be explained by the polyvagal theory. It’s probably also true that we are primed for connection, though again not in the way that polyvagal theory describes.

Finally, the vagus nerve is amazing in its own right; For example, 80-90% of its nerve fibers are afferent, meaning that they carry information from the body to the brain and not the other way around (Berthaud and Neuhuber, 2000). In this way, the vagus plays a central role in the transmission of information along the gut-brain axis (Breit et al., 2018; Enders, 2018).

I understand that the debunking of the polyvagal theory is difficult for nerdy, neuroscience-loving therapists to accept. Personally, I found it so disappointing that I had to process my emotions by drawing a tombstone. I encourage you to delve deeper for yourself into the primary sources I cite below.

References:

  • Berthoud, HR & Neuhuber, WL (December 2000). “Functional and chemical anatomy of the afferent vagal system.” Autonomic Neuroscience. 85 (1–3): 1–17. doi:10.1016/S1566–0702(00)00215–0. PMID 11189015. S2CID 30221339
  • Breit, S., Kupferberg, A., Rogler, G., & Hasler, G. (2018). Vagus nerve as modulator of the brain–gut axis in psychiatric and inflammatory disorders. Frontiers in psychiatry, 9, 44.
  • Cheng ZX, Guo SZ, Lipton AJ, and Gozal D. (2002). Domoic acid lesions in nucleus of the solitary tract: time-dependent recovery of hypoxic ventilatory response and peripheral afferent axonal plasticity. Journal of Neuroscience, 22: 3215–3226.
  • Cheng Z, Zhang H, Guo SZ, Wurster R, Gozal D. (2004). Differential control over postganglionic neurons in rat cardiac ganglia by NA and DmnX neurons: anatomical evidence. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 286:R625–33
  • Enders, G. (2018). Gut: The Inside Story of Our Body’s Most Underrated Organ (Revised Edition). Greystone Books Ltd.
  • Farmer DG, Dutschmann M, Paton JF, Pickering AE, McAllen RM. (2016). Brainstem sources of cardiac vagal tone and respiratory sinus arrhythmia. J Physiology, 594(24):7249–7265. doi:10.1113/JP273164.
  • Geis, G.S., & Wurster, R.D. (1980). Cardiac responses during stimulation of the dorsal motor nucleus and nucleus ambiguus in the cat. Circulation research, 46(5), 606–611.
  • Grossman, P., & Taylor, E.W. (2007). Toward understanding respiratory sinus arrhythmia: Relations to cardiac vagal tone, evolution and biobehavioral functions. Biological psychology, 74(2), 263–285.
  • Grossman, Paul. (2016). Re: After 20 years of “polyvagal” hypotheses, is there any direct evidence for the first 3 premises that form the foundation of the polyvagal conjectures?. Retrieved from: https://www.researchgate.net/post/After-20-years-of-polyvagal-hypotheses-is-there-any-direct-evidence-for-the-first-3-premises-that-form -the-foundation-of-the-polyvagal-conjectures
  • Monteiro, DA, Taylor, EW, Sartori, MR, Cruz, AL, Rantin, FT, & Leite, C. (2018). Cardiorespiratory interactions previously identified as mammalian are present in the primitive lungfish. Science advances, 4(2), eaaq0800. https://doi.org/10.1126/sciadv.aaq0800
  • Porges, S. W. (1995). Orienting in a defensive world: Mammalian modifications of our evolutionary heritage. A polyvagal theory. Psychophysiology, 32(4), 301–318.
  • Verberne, A.J. (2004). Differential cardiac parasympathetic innervation — what is the functional significance? American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 287(2), R485-R486.
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Article published in and translated and adapted for publication in .