Movement and sensory deficits may compromise neurogenesis in the post-natal stage of brain development

Recent findings in the field of neurobiology have elucidated that nervous system development and brain growth may be linked with movement and sensory input. The findings suggest that “mobility restrictions or insufficient sensory stimuli impact the production of new brain cells and brain development… “ and that “By testing whether early deficits in sensory experience similarly restrict human brain growth, our findings offer a novel approach to combatting such deficits to maintain normal brain development[1].”  Below, we explore the potential relevance of these new findings to the location and correction of vertebral subluxation in the pediatric population.

These two recent studies [2, 3], exploring neurogenesis in the presence and absence of either movement restriction or visual restriction, were performed in zebrafish – a popular and well-known choice for modeling human biology in a controlled research setting.  The zebrafish (Danio rerio) is a powerful model organism for the study of vertebrate biology, being well-suited to both developmental and genetic analysis [4] and has been used extensively to map vertebrate brain development. Therefore, while these findings have not yet been tested in humans, they clearly suggest the possibility that movement restrictions in the postnatal stage may be critical to brain development in vertebrates including humans, by potentially inhibiting neurogenesis. 

In humans, the first thousand days of life are said to be a critical point in a child’s development, “characterized by rapid rates of neuronal proliferation (cell numbers), growth and differentiation (complexity), myelination, and synaptogenesis (connectivity) [5].”  The first years of life for humans exhibit an elevated level of neuroplasticity compared to later stages of life, making experiences during this time period essential for cognitive, social, and physical development. These new zebrafish studies may, therefore, hold significant implications for human pediatric brain development, since this new information raises a possibility that movement and sensory input in the postnatal period may be especially important, with long-lasting impacts over the lifespan.

The studies were both undertaken by the same research group, with one team looking at the effect of movement on forebrain neurogenesis while the other looked specifically at the effect of visual sensory input on neurogenesis in the optic tectum [2, 3]. With regard to the former, the researchers remarked:

“Our results demonstrate the importance of movement in neurogenic brain growth and reveal a fundamental sensorimotor association that may couple early motor and brain development [3].” 

With regard to the second, they remarked: 

“Early brain development is shaped by environmental factors via sensory input; however, this form of experience-dependent neuroplasticity is traditionally studied as structural and functional changes within pre-existing neurons. Here, we found that restricting visual experience effects development of the larval zebrafish optic tectum, a midbrain structure involved in visually guided behavior, by limiting the survival of newly generated neurons. [author’s italics; 5]” 

Neurogenesis in a Nutshell 

Neurodevelopment follows seven basic stages, as follows [6]: 

1. Neurogenosis (the birth of a neuron)
2. Migration 
3. Differentiation
4. Maturity
5. Synaptogenesis (the birth of new synapses)
6. Synaptic pruning 
7. Myelinogenesis

These two new papers suggest that should motor and sensory input be suboptimal in the postnatal stage, then the process of neurodevelopment as a whole is diminished at the first of these seven developmental stages – and the authors show evidence that if neurogenesis is compromised, the resultant deficit may never be overcome [2, 3].  Specifically, comparative examination confirmed a difference in the size of the mature brains of the zebrafish populations studied, suggesting a resultant “glass ceiling” to neurodevelopment may result from a deficit of somatosensory input at this stage. 

In response to these recent research papers, Dr. Amy Haas remarked that “One reasonable extrapolation of this data is that, in the first critical weeks and months of a child’s life when neuronal proliferation is underway, ensuring optimal motor and sensory input may be critical.“ She went on to explore the following: 

“Movement maintains forebrain neurogenesis: what does that mean, in a practical sense? It means that if movement doesn’t happen, then neurogenesis, the birth of the new neurons that will create the circuitry of the brain, is compromised at step one of these seven stages of neurodevelopment.  Without proper sensory input, those neurons literally die. If those neurons die in the postnatal period because they have not had the right motor/sensory input, then one could reasonably assume that the brain cannot develop to optimal potential.  The neurons that were pruned, that’s like removing colors from a collection of crayons or markers representing the full-color spectrum. Without the full palette, any drawing produced will be missing elements, nuances – drawings will forever be limited to what is left.  Maybe that can be “enough,” per se… after all, the human nervous system is highly adaptable by its nature… but would it represent the optimal expression?     

“The field of neurodevelopment holds that the critical period for kids is the first thousand days. These new research papers put forward a new possibility, that perhaps there is a more critical period nestled within that.”

These two zebrafish studies independently show that in the absence of somatosensory input, neurons that would otherwise develop into brain networks are “pruned,” they do not regenerate or proliferate. Therefore, the brain may never achieve full differentiation into its complete array of brain structures. This essentially limits brain potential from the get-go, in the neurological sense – because structure dictates function.  What if the exact same process is true in humans? Well, that’s entirely possible if not probable. After all, zebrafish have long been used to study and understand the vertebrate nervous system, which includes… well, most of us. 

 

The Chiropractic Extrapolation

Even though zebrafish are a commonly used model in biology to predict human responses and reactions, there is the obvious disclaimer: this research hasn’t yet been repeated in humans. Obviously, studying neurogenesis and neuron pruning would be quite difficult to do in an ethical manner in the pediatric and infant population.

Still, the hypothesis remains that the zebrafish findings regarding neurogenesis could be very significant for human babies and their long term potential.

Keeping in mind that in the zebrafish model system, motion or sensory restriction led to neuron pruning and reduced neurogenesis, let’s consider a study by Keil and Fludder that described reduced range of motion present at birth [7].  In this study, reduced range of motion was found in: 

• 76.1% of infants born vaginally without intervention
• 75% of infants delivered with forceps
• 88.9% of vacuum-assisted deliveries
• 82.3% of infants born via caesarean section

While the sample may be slightly skewed given it was taken from a paediatric chiropractic clinic, it certainly shows that there is a population that suffers from reduced range of motion immediately following birth. Further, plagiocephaly, or flat head syndrome, is found in up to 46.6% of infants (according to a 2013 estimate) and this itself may result in motion restriction or motion asymmetry  [8]. 

Dr. Amy Haas explores what motion abnormality in neonates and pediatrics may mean for chiropractors when considered in the context of these new zebrafish studies: 

“When we look at the Keil and Fludder study, and other studies regarding range of motion abnormalities found directly following birth, we see that …whether birth trauma exists and results in motion abnormality is not in question. It’s a matter of assessing the degree of birth trauma: Is there torticollis? Is there a broken shoulder? Is there shoulder distortia? What other motion abnormalities can be appreciated upon exam?  Or, are there more subtle deficits?” says Dr. Amy. 

“These post-birth motion abnormalities are certainly not black and white, rather more shades of grey.  Some are very easily appreciated, while some are of a more subtle nature. Within that spectrum, we can include observations of a reduced range of motion due to a vertebral subluxation complex (VSC), as motion abnormality is one of the components of subluxation in the MOPI model. The findings of the zebrafish study support the philosophy that VSC may not constitute just a structural “stuckness” but rather, if it alters the somatosensory input to the brain, it may be literally interfering with brain development ipso facto via neurogenesis and neuron pruning mechanisms. People ask why you would need to check and adjust a baby, well these papers suggest the possibility that correcting vertebral subluxation complex in a newborn with motion abnormalities may restore the potential trajectory of neurogenesis.  In my opinion, that may be fairly important to human health, since we live our entire lives through our nervous systems.”

“In the human nervous system, input, when integrated, determines output. That’s the afferentation (or dysafferentation) loop. If you disturb the quality, quantity, or character of input to the brain, then you lack the appropriate input to be integrated to an appropriate and timely output.

“The findings in zebrafish establish that mobility restrictions or insufficient afferent sensory stimuli impacts the production and/or survival of new brain cells, and thereby limit the development of the nervous system. Extrapolated to human biology, and particularly to human babies born with birth trauma, well, these findings may point to the broader potential implication of the Vertebral Subluxation Complex.  VSC, particularly from birth trauma, may be literally limiting human development.”

“This potentially makes infants and paediatrics the most significant time window in terms of chiropractic care having an impact on optimal neural development across the lifespan. The existence of birth trauma and resultant motion abnormality is not refutable. It has been clearly documented. When you look at that in the context of this paper you see the possibility that motion abnormalities could, in theory, limit brain and nervous system development.  Clearly, research will be necessary to explore this potential connection… that said, my own clinical experience and that of other field docs is consistent with this possibility. In my observation and that of colleagues, babies who are checked for VSC and adjusted as necessary from birth develop faster, are more alert and interactive and meet milestones ahead of same-age cohorts who have never been adjusted.  Now, that’s a big statement, and I get that. I’ll offer again, this is my personal observation and that of many other field docs, and it’s one that I find very interesting. I believe that observation merits further exploration, in the context of this recently published zebrafish research.”

Where does this leave us on sensory input?

Research conducted by Dr. Heidi Haavik, Dr. Kelly Holt and the New Zealand College of Chiropractic has illustrated over and over again that sensorimotor integration is clearly and positively impacted by the chiropractic adjustment [9,10]. 

Says Dr. Amy, “Published chiropractic research by multiple authors and groups has established that the chiropractic adjustment can affect afferent input, sensorimotor integration, and efferent (motor) output.  In a simpler sense, think about nociception and proprioception. When you have nociception, which is generated by an abnormally moving spinal motion segment or a nonmoving spinal joint, well, that counters proprioception. It is this proprioception that the authors are talking about (in these zebrafish studies) which enables neuronal survival. To suggest that somatosensory input directs human brain development and that its deficit (via VSC) may limit brain development is an extrapolation, but this recent research finding in the zebrafish certainly sets an interesting precedent towards that idea.”

“Taking this a step further, if kids are denied access to chiropractic care, it’s possible that they will never reach their full range of human potential – biologically and neurologically speaking. It follows that if sensory and motor problems can be corrected in newborns via the chiropractic adjustment intended to correct VSC and thereby restore somatosensory input, which would, in turn, be expected to promote normal brain development…. well, in my opinion, it makes no sense to ban chiropractic care for kids. It could actually be unethical, in fact, to restrict that form of care. Especially considering that excellent safety records support the conservative chiropractic care of children, by those specifically trained in this art [11]” said Dr Amy.  “The safety of this care, when properly delivered, has been established – and the benefits may, in fact, be much greater than originally thought.” 

Or, to paraphrase the conclusion of the study’s author [3], “Our results demonstrate a robust connection between motor and brain development during postembryonic development. Motor development in most vertebrates begins early in the postembryonic period… Therefore, if conserved across taxa, this close relationship between movement and neurogenesis may couple early motor and brain development. Furthermore, this relationship could help explain correlations between early physical and mental development, such as the long-observed comorbidity of physical and mental impairments… and correlation between sedentary lifestyle and depression… which has been previously associated with impaired neurogenesis in children.”

Perhaps it’s time to reconsider the potential importance of paediatric chiropractic care to human potential in light of developmental biology and to explore this possibility with due research diligence.

The Australian Spinal Research Foundation would like to thank Dr. Amy Haas for her extensive insight and input on this article.

REFERENCES: 

1. University of Toronto. “Scientists uncover connection between post-natal sensory experiences and brain development: Findings reveal opportunities for interventions to overcome barriers to cognitive development.” ScienceDaily. ScienceDaily, 16 April 2018. www.sciencedaily.com/releases/2018/04/180416124313.htmRetrieved 2 April 2019
2. Hall ZJ and Tropepe V (2018), “Movement maintains forebrain neurogenesis via peripheral neural feedback in larval zebrafish,” eLife, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5847330/?fbclid=IwAR3PRQCnqFl2YPIqhsdFhTVxE6SRuFyl6BuIgcMLaI0xyfD1b9bHExrHwRIretreived 2 April 2019
3. Hall ZJ and Tropepe V (2018), “Visual experience facilitates BDNF-Dependent Adaptive Recruitment of New Neurons in the Postembyronic Optic Tectum,” The Journal of Neuroscience, February 21 2018, 38(8): 2000-2014, http://www.jneurosci.org/content/jneuro/38/8/2000.full.pdf?fbclid=IwAR0NGjYOJsveXah6MLloINDFFpYIKoG8zZGtd04JjGDRXzqYF0X7jx9yd18retrieved 2 April 2019
4. Dooley K, Zon L (2000), “Zebrafish: a model system for the study of human disease,” Curr Opin Genet Dev.2000 Jun;10(3):252-6, https://www.ncbi.nlm.nih.gov/pubmed/10826982retrieved 4 August 2019
5. Cusick S and Georgieff M, “The First 1000 days of life: the brains window of opportunity,” UNICEF, https://www.unicef-irc.org/article/958-the-first-1000-days-of-life-the-brains-window-of-opportunity.htmlretrievied 2 April 2019
6. Staff Writer (2019), “Interview with Dr Monique Andrews” Australian Spinal Research Foundation
7. Fludder C, and Keil B (2018), “Instrument Assisted Delivery and the Prevalence of Reduced Cervical Spine Range of Motion,” Chiropractic Journal of Australia, retrieved 28 November 2018
8. Mawji A, Robinson Vollman A, Hatfield J, McNeil A, Sauve R, (2013), “The Incidence of Positional Plagiocephaly: a Cohort Study,” Pediatrics, August 2013 Volume 132, Iss. 2  https://pediatrics.aappublications.org/content/132/2/298 
9. Holt, Kelly R et al,“Effectiveness of Chiropractic Care to Improve Sensorimotor Function Associated With Falls Risk in Older People: A Randomized Controlled Trial,” Journal of Manipulative and Physiological Therapeutics.
10. Staff writer, (2016) “Beyond Reasonable Doubt: Adjusting the spine changes the brain,” Australian Spinal Research Foundation, https://spinalresearch.com.au/research-beyond-doubt-adjusting-subluxated-spine-changes-brain-function/  
11. Todd A, Carroll M, Robinson A, Mitchell E, (2015), “Adverse Events Due to Chiropractic and Other Manual Therapies for Infants and Children: A Review of the Literature,” Journal Manipulative and Physiological Therapeutics, Volume 38, Issue 9, November-December 2015, pp. 699-712, http://www.sciencedirect.com/science/article/pii/S016147541400178X