Chiropractors can tout some crazy claims about the ability for an adjustment to heal people, but what does the evidence say about adjustments and brain function? Lets find out!

The Literature Low-Down

This segment is meant to give you the skinny; the short and simple; the low-down on a noteworthy scholarly article from a number of different scientific journals to give you the knowledge and power to take your health into your own hands (within reason).
 

THE LITERATURE

Today we are going to go over “Spinal Manipulation Therapy: Is it all about the brain? A current review of the neurophysiological effects of manipulation” written by Giles Gyer at The London College of Osteopathic Medicine along with their colleagues Jimmy Michael, James Inklebarger, and Jaya Shanker Tedla.

It was published in the Journal of Integrative Medicine on 04/22/2019. The Journal of Integrative Medicine has an average impact factor of around 1.20. The impact factor basically gives you an estimation of how popularly cited the articles in the journal are and by proxy its reputation in the academic community. The most popular journal in the world, The New England Journal of Medicine, has an impact factor of around 70. It is important to note, the impact factor does not tell you anything about the content or validity of each of the articles written in the journal, just its popularity. Just like social media, the more popular journals have more reach and publicity than less popular journals.

This means that this information in this article might not be known by your healthcare provider due to the limited amount of time this article has been available and the reach of the journal. With those caveats out of the way, let’s dive into it.
 

THE LOW-DOWN

Chiropractors have been around officially for over 100 years but “Bone Setters” have been around since the Egyptians and are documented in the oldest medical text written in the 1500s. Most are aware of the beneficial effects of manipulation on pain and mobility but there are still disputes in the medical field on why these effects happen. In this paper, experts search the medical literature to review the effects of manipulation on the nervous system and the cascade of events that follow due to that stimulation of the nervous system.
 

STUDY DESIGN

This narrative review covers over 100 articles to bring an updated model of how spinal manipulations (ie. chiropractic adjustments) affect the nervous system. They cover a number of topics including the effects on general neurophysiology, neuromuscular integration, autonomic function, and pain inhibition.

At the beginning of the article, the authors also criticize the traditional theories of why chiropractic manipulation works. Studies show that the increase in segmental motion in the spine is transient and no evidence has shown lasting positional change. The model posed by this

They also bring to light that the palpation of spinal fixations has poor inter-rater reliability. This means that between 2 examiners, there will be a greater variation in findings even on the same patient. It is important to note that spinal palpation does have high intra-rater reliability which means the same examiner will find the same findings on those who have the same fixations. This illustrates the fact that regardless of the therapeutic method or philosophy of the practitioner, The input to the nervous system is similar and elicits similar effects
 

RESULTS

Let’s cover each section of the effects listed by the authors.
 

GENERAL NEUROPHYSIOLOGY

There are complex interactions between the Central Nervous System (CNS) which constitutes the brain and spinal cord, and the Peripheral Nervous System (PNS) which are nerves. Spinal Manipulation influences these complex interactions by activating sensory neurons through the maneuver and the changes in spinal biomechanics. The sensory information changes the integration not only in the spinal cord but in higher brain centers to affect our motor, nociceptive (pain), and autonomic systems.
 

NEUROMUSCULAR INTEGRATION

Spinal manipulation exerts changes on our motor system through a number of mechanisms; There are changes in muscle activation and modulation of both alpha- and gamma-motor neurons.

Alpha-motor neurons are the ones that actually tell the muscle to perform a motor activity. When a joint is injured the muscles that cross that joint spasm to stabilize the joint and reduce further damage. This spasm also increases pain. Adjustments reset the excitability of these neurons and reduce spasm. Although the excitability is reduced, studies have shown the maximum motor evoked potential (brain output to the motor system) increases after spinal manipulation.

Gamma-motor neurons are the alpha-motor neuron’s nerdy sibling. They are less numerous than motor neurons but their job is to celebrate muscle spindles. Muscle spindles are located in every muscle and tell the nervous system how much tension is in the muscle. The more tension in the muscle spindle, the more sensitive it is to stretch. When people test your reflexes they are testing your gamma-motor neuron.

Gamma-motor neurons talk directly to alpha-motor neurons and affect their excitability. Spinal manipulation calms gamma motor neurons and thus stretch reflex hyperactivity that is leading to the muscular spasm
 

AUTONOMIC FUNCTION

First, the Autonomic Nervous System (ANS) controls internal body responses to maintain homeostasis and is mostly unconscious. It regulates things like heart and respiratory rates, blood pressure, and pupillary responses as well as all the smooth muscle in basically all of your organs like your heart, lungs, digestive system, and kidneys. The most famous part of the ANS is the Vegas Nerve.

Because the ANS potentially interacts with the nociceptive (pain) system, spinal manipulation treating pain can affect the ANS but literature has also shown a direct effect with not only symptomatic but asymptomatic patients. Changes have been seen in skin blood flow, blood pressure, pupillary reflexes and heart rate variability (HRV).

It is unclear and disputed whether the Sympathetic Nervous System (SNS), the “Fight-or-Flight” system, or the Parasympathetic Nervous System (PSNS), the “Rest-and-Digest” system, is facilitated with spinal manipulation. Multiple studies have shown increases in either PSNS and SNS activation. Imaging studies of the brain do show that areas related to the control and modulation of the ANS like the anterior cingulate cortex, inferior prefrontal cortex, and cerebellar vermis are affected by manipulation.

The ANS also influences the immune system through the Hypothalamic-Pituitary-Adrenal (HPA) axis that secretes hormone messengers like cortisol; which has been shown to increase in the blood immediately following an adjustment.
 

PAIN (NOCICEPTIVE) INHIBITION

The pain reduction (hypoalgesic) effect of spinal adjusting is considered to be caused by four mechanisms. Segmental inhibition of pain, activation of descending inhibitory pathways, non-specific cerebral responses, and temporal summation.
 

Segmental Inhibition

Better known as the Pain Gait theory developed by Melzack and Wall in the 1960s; this theory states that small-diameter, A-delta and C, sensory (pain) fibers activate a part of the spinal cord, substantia gelatinosa; where large diameter, A-beta, sensory (proprioceptive) fibers inhibit the activation of the substantia gelatinosa. It’s like when you stub your toe and then proceed to rub it. The proprioceptive information blocks the pain fibers from activating your spinal cord.
 

Descending Inhibition

Studies have shown that spinal adjustments stimulate inhibitory pathways that originate in your brainstem, specifically the Periaqueductal Grey (PAG) and Rostral Ventromedial Medulla (RVM). These centers project down to the spinal cord and inhibit pain the same as proprioceptive neurons from the periphery but they use different neurotransmitters which goes beyond the scope of this blog post. Interestingly it has been shown that different types of manipulation activate different inhibitory pathways and can be one of the reasons why individuals respond to different adjusting techniques.
 

Non-Specific Cerebral Responses

You gotta love the placebo effect. Just the fact that you are seeking care may give your body an excuse to inhibit pain. We cannot forget the psychosocial factors that play into going to the chiropractor for some sort of pain and expecting to feel better, especially if your adjustment has an audible cavitation (crack).
 

Temporal Summation

When a neuron in the spinal cord is exposed to repetitive painful stimuli of the same amplitude and frequency for long enough it will experience temporal summation or “wind-up”. This sensitization of the nerve then lowers the threshold to activation meaning if I needed 10 pounds of pressure to “activate” pain, I would only need 8 or 5 pounds to reach the same activation. Spinal adjusting reduces the temporal summation and thus decrease this “wind-up”
 

TAKE-AWAYS

The chiropractic adjustment is such a powerful tool and this article adds to the evidence supporting its use. With all the above mechanisms in play, we can see how the adjustment can play a beneficial role in many of the issues that chiropractors are known for like pain and muscle spasm.

But this article illustrates how chiropractics can affect many more issues. The evidence, specifically imaging studies, showing changes in cortical and subcortical regions of the brain means that chiropractic could influence dysfunctions in those areas and the functions they control indirectly.

We know that some chiropractors tout that an adjustment can help with things like ADHD, Autism, Asthma, Depression, Balance, GERD, Crohn’s, and many other conditions that those of a conventional medical mindset scoff at. Prefrontal cortical activation, from an adjustment, could help with ADHD and depression; cerebellar stimulation affects autism and balance; stimulation and modulation of the ANS can help asthma, GERD, and Crohn’s.

I don’t feel like I need to say it but I will just to make sure that we are all on the same page. YOU SHOULD NOT RELY ON CHIROPRACTIC TO SOLELY TREAT AND MANAGE THESE CONDITIONS! There are many more proven and effective tools for the treatment of the examples provided above. I just wanted to show that, for the data, chiropractic can influence more than just musculoskeletal and biomechanical issues.

Having a plan on how to best support these factors should be something you discuss with your healthcare provider. If you or someone you know is dealing with a medical issue that isn’t resolving, I’d ask you to give chiropractic a try as well as share this blog and spread the knowledge. For access to the article Click Here. If you have any other questions or comments, please leave a comment so a discussion can take place and those answers can help other people.

Dr. Chase Davidson, DC is a Board Eligible Chiropractic Neurologist and specializes in concussion and sports rehab, as well as functional medicine and immunology. He is the Director of Neuroscience and Metabolics at Action Potential – Sports and Neurological Rehab. He also is a member of the International Association of Functional Neurology and Rehabilitation (IAFNR). Stay connected with Dr. Davidson on Linkedin: @dr-davidson / Instagram: @thatneurologyguy / Email: dr.chase@actionpotentialcenter.com

Visit us at Action Potential - Sport & Neuro Performance across our multiple offices across the Austin, Texas area. Call today at (512) 686-6611 to get scheduled for an appointment at our offices located in Lumos Fitness Collective, Defiant CrossFit, & Black Metal CrossFit

Bibliography

This Article

Gyer, G., Michael, J., Inklebarger, J., & Shanker Tedla, J. (2019). Spinal manipulation therapy: is it all about the brain? A current review of the neurophysiological effects of manipulation. Journal of Integrative Medicine. doi:10.1016/j.joim.2019.05.004
 

Other Supporting Articles

• Haavik H, Niazi I, Jochumsen M, Sherwin D, Flavel S, Türker K. Impact of spinal manipulation on cortical drive to upper and lower limb muscles. Brain Sci 2016;7(1):2.

• Kovanur Sampath K, Mani R, Cotter JD, Tumilty S. Measureable changes in the neuro-endocrinal mechanism following spinal manipulation. Med Hypotheses 2015;85(6):819–24

• Schmid A, Brunner F, Wright A, Bachmann LM. Paradigm shift in manual therapy? Evidence for a central nervous system component in the response to passive cervical joint mobilisation. Man Ther 2008;13(5):387–96.

• Colloca CJ, Keller TS, Harrison DE, Moore RJ, Gunzburg R, Harrison DD. Spinal manipulation force and duration affect vertebral movement and neuromuscular responses. Clin Biomech (Bristol, Avon) 2006;21(3):254–62.

• Colloca CJ, Keller TS, Gunzburg R. Biomechanical and neurophysiological responses to spinal manipulation in patients with lumbar radiculopathy. J Manipulative Physiol Ther 2004;27(1):1–15.

• Coppieters MW, Butler DS. Do ‘sliders’ slide and ‘tensioners’ tension? An analysis of neurodynamic techniques and considerations regarding their application. Man Ther 2008;13(3):213–21.

• Funabashi M, Kawchuk GN, Vette AH, Goldsmith P, Prasad N. Tissue loading created during spinal manipulation in comparison to loading created by passive spinal movements. Sci Rep 2016;6:38107.

• Bialosky JE, George SZ, Bishop MD. How spinal manipulative therapy works: why ask why? J Orthop Sports Phys Ther 2008;38(6):293–5.

• Walker BF, Koppenhaver SL, Stomski NJ, Hebert JJ. Interrater reliability of motion palpation in the thoracic spine. Evid Based Complement Alternat Med 2015;2015:815407.

• Seffinger MA, Najm WI, Mishra SI, Adams A, Dickerson VM, Murphy LS, et al. Reliability of spinal palpation for diagnosis of back and neck pain: a systematic review of the literature. Spine (Phila Pa 1976) 2004;29(19): E413–25.

• Padayachy K, Vawda GH, Shaik J, McCarthy PW. The immediate effect of low back manipulation on serum cortisol levels in adult males with mechanical low back pain. Clin Chiropr 2010;13(4):246–52.

• Plaza-Manzano G, Molina F, Lomas-Vega R, Martínez-Amat A, Achalandabaso A, Hita-Contreras F. Changes in biochemical markers of pain perception and stress response after spinal manipulation. J Orthop Sports Phys Ther 2014;44 (4):231–9.

• Daligadu J, Haavik H, Yielder PC, Baarbe J, Murphy B. Alterations in cortical and cerebellar motor processing in subclinical neck pain patients following spinal manipulation. J Manipulative Physiol Ther 2013;36(8):527–37.

• Taylor HH, Murphy B. Altered central integration of dual somatosensory input after cervical spine manipulation. J Manipulative Physiol Ther 2010;33 (3):178–88.

• Melzack R, Wall PD. Pain mechanisms: a new theory. Science 1965;150 (3699):971–9.

• Randoll C, Gagnon-Normandin V, Tessier J, Bois S, Rustamov N, O’Shaughnessy J, et al. The mechanism of back pain relief by spinal manipulation relies on decreased temporal summation of pain. Neuroscience 2017;349:220–8.

• Anderson RJ, Craggs JG, Bialosky JE, Bishop MD, George SZ, Staud R, et al. Temporal summation of second pain: variability in responses to a fixed protocol. Eur J Pain 2013;17(1):67–74.

• Liu, W., Ge, T., Leng, Y., Pan, Z., Fan, J., Yang, W., & Cui, R. (2017). The Role of Neural Plasticity in Depression: From Hippocampus to Prefrontal Cortex. Neural plasticity, 2017, 6871089. https://doi.org/10.1155/2017/6871089