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The brain-body axis is no straight line

axial twist axis decussation Feb 23, 2024
 

 

Harmonizing with the asymmetry of somatic experience


You have likely heard of the HPA axis (1) and the gut-brain axis (2) as physical culture wakes up to direct links between chronic stress and poor health outcomes. The conceptual axis linking the brain and body follows the same logic. The brain-body axis is simply the bidirectional route of communication between your mind and body. Thinking of physiological phenomena this way – as relationships rather than parts –  is a hallmark of the continuing paradigm shift in physical culture. 

Anatomists have classically broken down the study of anatomy into two main perspectives: systems and regional. A regional focus divides the body up into regions such as the axilla, upper & lower limb, abdominal, and pelvic. When we teach systems anatomy, we’re placing the focus on organ systems such as the cardiovascular or integumentary. In recent years, the world has been waking up to the connections among systems – the physiology of connectedness.

Connections amongst systems happen chemically and morphologically as well as psychologically. This piece will focus on the spiraling morphology of physiologic systems, specifically the nervous and locomotor interaction. Morphology is the study of shape in anatomy… and evolution demonstrates the twisty tale of shape development at every timescale. If you’re fascinated with how structure and function give rise to the human somatic experience, you need to know about the somatic twist.

Before we dive any deeper, let’s get our assumptions clear. I’m assuming you are familiar with the concept of fascia as the most richly innervated sensory organ (5) contributing to and largely defining our dynamical and constantly updating picture of reality. The extracellular matrix (ECM) and fascia are terms talking about structural tissue, the “smart” material that forms a dual carriageway of communication: between the body and the brain. But how did the body become so brainy? And how did the brain get so… twisted?

That fascia is positively replete with mechanoreceptors is important to building up the picture around the twisted brain-body axis and, crucially, our human experience of such a fundamental curl. Look around the movement community - we as humans enjoy an incredible range of motion that we love to keep pushing into extremes of spiral motion. But this post is not about fancy human tricks… it’s about the fact that we’re coiled at our very structural axis, simply sitting still. And in that simple spiral, we share common origins with our friend the goat. 

It’s true: this balletic bipedal human story shares millions of years of evolution with our quadruped family, four-legged multicellular beings with segmented spines. The “somatic twist model” is a theory of how we (by ‘we’ I mean humans, goats, and all other vertebrates) transitioned from our common invertebrate origins. According to the Axial Twist Hypothesis (ATH), we vertebrates share an intriguing plot twist. 

But first, a little backstory.


Two examples of invertebrate nervous system organization: A) Flatworm system, the simplest linear-type nervous system of two nerves connected to a complex neuronal network. B) Nerve net of radiates, the simplest neural organization.

 

The vertebrate nervous systems of quadrupeds have evolved to sit behind the gut tub, dorsally.

Whereas the ventral nervous system of a grasshopper, for example, sits ventrally in front of the gut tube. Image copyright 2014 Encyclopædia Brittanica.


 

All Front to Back

One of the remaining mysteries of the brain is the contralateral organization of the forebrain with the itinerant crossings of its major afferent (sensory) and efferent (motor) connections. These crossings are known as decussations, from the Latin ‘dec’ for ten, the X shape underpinning our central nervous system organisation. Two relatively recent studies by Kinsbourne (6) and de Lussanet (7), have proposed that the forebrain – and its neural continuities through the optic chiasm – is rotated by 180° with respect to the rest of the body, giving rise to the large-scale decussation pattern. 

Kinsbourne first proposed the idea of a 180-degree twist in an early abstract (1978) under the working name of somatic twist theory. The concept was independently progressed into a developmental and evolutionary model as the Axial Twist Hypothesis (ATH) by De Lussanet & Osse (2012 & 2015)(6).

This notion (described in Kinsbourne’s Somatic Twist Theory and deLussanet & Osse’s Axial Twist Hypothesis) challenges the received assumptions about decussation and bilateral symmetry. The theories instead posit that the neuraxis inverted its position as an evolutionary strategy, moving from ventral (back) to dorsal (front) employing an epic evo-devo twist. The twisting of the body 180° on its axis just behind its anterior pole, aligning the neuraxis with the dorsal head ganglia and brain, has effectively twirled the coattails of our smart suit. Like a spinning comet, the twisting of the nerve tracts brought along decussation in its wake.

De Lussanet et al (2019) later found lovely evidence for their theory by employing a rather romantic experiment (7). They predicted and found a right-sided bias for hugging (78%) and a left-sided bias for kissing (69%), confirming their argument that humans are fundamentally asymmetric. My thoughts are that hugging and kissing count as spiral motion, offset as they are around the neuraxis, and contributing crucially to feelings of connectedness and well-being. Going a step further – is this evidence of consciousness curling to experience itself in the form of human connection?

Considering our twirled neuraxis and the fascial system as its throughvelope (as opposed to envelope), I’m seeing the locomotor tissue as a continuation of the decussation pattern. We are fundamentally asymmetrical, with various cell populations and tissues spun in opposing directions on growth differentials that form the dance of tension and compression forces, giving rise to the sum somatic experience. 

Put simply: we are fundamentally woven on a spiral loom, and practices that are tuned into rotational, rhythmic movement are optimized for healing. Our bodies seem to recognize and trust the helical motif of Nature.

To harmonize with your cosmic curl, I recommend three potent yet often accessible practices. Please note: where the suggestion of hugging and kissing is going to be triggering for you, I recommend skipping number one.

  1. Hugging and kissing. OK so be discerning here, hope that goes without saying! The research abounds with evidence for the anti-aging, pro-wellbeing effects of loving kindness in all its forms, especially hugs (9; 10, 11). As we have seen in the work of de Lussanet et al (2019), the very act of hugging and kissing is also an ode to our innate twisted neuraxis. Hugs give us a way to celebrate that twirl around one another, to feel held and to hold with the curl of being human.
  2. Movement constrained for rotation. Again, it doesn’t have to be fancy. Simply rolling around on the floor and exploring how your joints roll and glide is enough to tap into the body’s spirality. The rhythmicity can come into resonance with our oscillating cellular activity and promote healing. Add load and make it hypertrophic. Change intensity and develop cardiovascular and circulatory benefits. Bag extra euphoria points if you happen to be rolling and gliding in close proximity to someone else or within a community where you feel safe and supported. 
  3. Walking in Nature. Walking is rhymical and helical, harnessing orthograde (cross-body) rotational power through the spinal engine (thanks, Gracovetsky!)(12). The benefits of walking for mental and physical health are well documented in the literature. When we are fortunate enough to access the natural world on paths less traveled, the benefits of gratitude and wonder are like compound interest. 

In short, harmonizing with your twisted brain-body axis is to love, move well, and practice gratitude. Feel the curly axis of your locomoting nervous system yields dividends to shore up the weary soul repeatedly saddened by traumatic world events. 

It is a frightening time on our planet, and not just for vertebrates. We need to raise awareness of practices that can put our community in touch with more than just the nuts and bolts of psychology, but the powerful knowledge that can change minds and habits.


References

  1. Margolis KG, Cryan JF, Mayer EA. The Microbiota-Gut-Brain Axis: From Motility to Mood. Gastroenterology. 2021 Apr;160(5):1486-1501. doi: 10.1053/j.gastro.2020.10.066. Epub 2021 Jan 22. PMID: 33493503; PMCID: PMC8634751.
  2. Packard AE, Egan AE, Ulrich-Lai YM. HPA Axis Interactions with Behavioral Systems. Compr Physiol. 2016 Sep 15;6(4):1897-1934. doi: 10.1002/cphy.c150042. PMID: 27783863; PMCID: PMC7219962.
  3. Theise, Neil. Notes on Complexity: A Scientific Theory of Connection, Consciousness, and Being. United States, Spiegel & Grau.
  4. Shuna SONG, Zhensu SHE. Quantum theory-based physical model of the human body in TCM, Digital Chinese Medicine, Volume 5, Issue 4, 2022, Pages 354-359, ISSN 2589-3777, https://doi.org/10.1016/j.dcmed.2022.12.002
  5. Schleip, Robert. The Fascial Network: Our Richest Sensory Organ. International Journal of Therapeutic Massage & Bodywork Research Education & Practice. 2023. 40-51.
  6. Kinsbourne M. Somatic twist: a model for the evolution of decussation. Neuropsychology. 2013 Sep;27(5):511-5. doi: 10.1037/a0033662. PMID: 24040928. 
  7. de Lussanet MH, Osse JW. Decussation as an axial twist: A comment on Kinsbourne (2013). Neuropsychology. 2015 Sep;29(5):713-4. doi: 10.1037/neu0000163. Epub 2014 Dec 22. PMID: 25528610.
  8. de Lussanet MHE. Opposite asymmetries of face and trunk and of kissing and hugging, as predicted by the axial twist hypothesis. PeerJ. 2019 Jun 7;7:e7096. doi: 10.7717/peerj.7096. PMID: 31211022; PMCID: PMC6557252.
  9. Benameur T, Panaro MA, Porro C. The antiaging role of oxytocin. Neural Regen Res. 2021 Dec;16(12):2413-2414. doi: 10.4103/1673-5374.313030. PMID: 33907023; PMCID: PMC8374585.
  10. Rogers-Jarrell T, Eswaran A, Meisner BA. Extend an Embrace: The Availability of Hugs Is an Associate of Higher Self-Rated Health in Later Life. Res Aging. 2021 May;43(5-6):227-236. doi: 10.1177/0164027520958698. Epub 2020 Sep 14. PMID: 32924800.
  11. Murphy MLM, Janicki-Deverts D, Cohen S. Receiving a hug is associated with the attenuation of negative mood that occurs on days with interpersonal conflict. PLoS One. 2018 Oct 3;13(10):e0203522. doi: 10.1371/journal.pone.0203522. PMID: 30281606; PMCID: PMC6169869.
  12. Gracovetsky SA, Iacono S. Energy transfers in the spinal engine. J Biomed Eng. 1987 Apr;9(2):99-114. doi: 10.1016/0141-5425(87)90020-3. PMID: 3573762. 

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