Were D.D. and B.J. Palmer right with their bone on nerve theory? According to Charles A. Lantz, DC. PhD. Director of Research, Life Chiropractic College West (2015), Montgomery and Nelson cited the context within which medical authors in the mid- to late 19th century referred to subluxation, one that was similar to how D.D. Palmer later would:
A vertebra is said to be displaced or luxated when the joint surfaces are entirely separated. Sub-luxation is a partial or incomplete separation: one in which the articulating surfaces remain in partial contact. This latter condition is so often referred to and known by chiropractors as sub-luxation. The relationship existing between bones and nerves are so nicely adjusted that anyone of the 200 bones, more especially those of the vertebral column, cannot be displaced ever so little without impinging upon adjacent nerves. Pressure on nerves excites, agitates, creates an excess of molecular vibration, whose effects, when local, are known as inflammation, when general, as fever. A subluxation does not restrain or liberate vital energy. Vital energy is expressed in functional activity. A subluxation may impinge against nerves, the transmitting channel may increase or decrease the momentum of impulses, not energy.
Lance (2015) also reported, “According to BJ Palmer, a subluxation represented a displaced bone that impinged on a nerve, thus interfering with the transmission of vital nerve energy (or, more specifically, the transmission of ‘mental impulses.’)”
For over a century, doctors of chiropractic have been explaining chiropractic by teaching patients and the medical community that there are bones compressing/irritating spinal nerves. The ensuing nervous system dysfunctions have negative effects on the function of peripheral nervous systems, central nervous systems and patients’ overall ability to maintain homeostasis. Essentially, they go into states of dis-ease. These discussions were in large part due to the teachings of D.D. Palmer and B.J. Palmer as previously cited. Based on the results rendered in chiropractic offices across the country and in a patient-driven model of success, the general consensus in both private practice and chiropractic academia had been to maintain status quo and simply teach what has worked in the absence of conclusive evidence, particularly in light of a lack of serious governmental funding and support for chiropractic research. In addition, dogma has also created blinders for many, as evidence evolves to further chiropractic and its understanding, application and expansion.
“The areas of the brain affected by chiropractic adjustments effect the following functions: emotions, learning, motivation, memory, consciousness, homeostasis, perception, motor control, self-awareness, cognitive function, voluntary movements, decision making, touch, temperature, pain of the skin- epithelial tissue-skeletal muscles-bones-internal organs and cardiovascular system.”
Over the last 10-15 years, research has been published by the scientific community that has begun to verify that D.D. and B.J. Palmer’s hypotheses were fundamentally correct, while clarifying the specific physiological mechanisms related to chiropractic’s ability to alleviate pain. As a result of initially studying pain mechanisms, contemporary research has also begun to set the foundation for understanding why chiropractic works with systemic and autonomic dysfunction and potential disease treatment through the adjustment – central nervous system connection. It is the understanding of that connection with pain that is helping people to begin to understand the full impact of the chiropractic spinal adjustment and render the evidence to help more get well.
CENTRAL NERVOUS SYSTEM PROCESSING OF PAIN REDUCTION
Coronado et al. (2012) reported that, “Reductions in pain sensitivity, or hypoalgesia, following SMT [spinal manipulative therapy or the chiropractic adjustment] may be indicative of a mechanism related to the modulation of afferent input or central nervous system processing of pain” (p. 752). “The authors theorized the observed effect related to modulation of pain primarily at the level of the spinal cord since (1) these changes were seen within lumbar innervated areas and not cervical innervated areas and (2) the findings were specific to a measure of pain sensitivity (temporal summation of pain), and not other measures of pain sensitivity, suggesting an effect related to attenuation of dorsal horn excitability and not a generalized change in pain sensitivity” (Coronado et al., 2012, p. 752). These findings indicate that a chiropractic spinal adjustment affects the dorsal horns at the root levels which are located in the central nervous system. This is the beginning of the “big picture” since once we identify the mechanism by which we can positively influence the central nervous system, we can then study that process and its effects in much more depth.
One of the main questions asked by Corando et al. (2012) “…was whether SMT (chiropractic adjustments) elicits a general response on pain sensitivity or whether the response is specific to the area where SMT is applied. For example, changes in pain sensitivity over the cervical facets following a cervical spine SMT would indicate a local and specific effect while changes in pain sensitivity in the lumbar facets following a cervical spine SMT would suggest a general effect. We observed a favorable change for increased PPT [pressure pain threshold] when measured at remote anatomical sites and a similar, but non-significant change at local anatomical sites. These findings lend support to a possible general effect of SMT beyond the effect expected at the local region of SMT application (p. 762).
The mechanisms of SMT are theorized to result from both spinal cord mediated mechanisms and supraspinal mediated mechanisms [brain]. A recent model of the mechanisms of manual therapy suggests changes in pain related to SMT result from an interaction of neurophysiological responses related to the peripheral nervous system and the central nervous system at the spinal and supraspinal level” (Coronado et al., 2012, p. 762). This demonstrates that the chiropractic adjustment influences the peripheral nervous system and the central nervous system. “Collectively, these studies provide evidence that SMT has an immediate effect on reducing pain sensitivity, most notably at the remote region of stimulus assessment with similar results in clinical and healthy populations” (Coronado et al., 2012, p. 763).
Reed, Pickar, Sozio, and Long (2014) reported:
…forms of manual therapy have been clinically shown to increase mechanical pressure pain thresholds (i.e., decrease sensitivity) in both symptomatic and asymptomatic subjects.Cervical spinal manipulation has been shown to result in unilateral as well as bilateral mechanical hypoalgesia. Compared with no manual therapy, oscillatory spinal manual therapy at T12 and L4 produced significantly higher paraspinal pain thresholds at T6, L1, and L3 in individuals with rheumatoid arthritis. The immediate and widespread hypoalgesia associated with manual therapy treatments has been attributed to alterations in peripheral and/or central pain processing including activation of descending pain inhibitory systems.
Increasing evidence from animal models suggests that manual therapy activates the central nervous system and, in so doing, affects areas well beyond those being treated. (p. 277)
Reed et al. (2014) also reported:
The finding that only the higher intensity manipulative stimulus (ie, 85% BW [body weight] vs 55% BW or control) decreased the mechanical sensitivity of lateral thalamic neurons to mechanical trunk stimulation coincides with other reports relating graded mechanical or electrical stimulus intensity to the magnitude of central inhibition…
Several clinical studies indicate that spinal manipulation [chiropractic spinal adjustment] alters central processing of mechanical stimuli evidenced by increased pressure pain thresholds and decreased pain sensitivity in asymptomatic and symptomatic subjects following manipulation. (p. 282)
The thalamus also plays an important role in regulating states ofsleep and wakefulness.Thalamic nuclei have strong reciprocal connections with the cerebral cortex, formingthalamo-cortico-thalamic circuitsthat are believed to be involved withconsciousness. The thalamus plays a major role in regulating arousal, the level of awareness, and activity (“Thalamus,” http://en.wikipedia.org/wiki/Thalamus).
This indicates that the chiropractic spinal adjustment reduces pain by effecting the thalamus and descending central pain pathways, while mobilization does not show evidence of having the same effect. In addition, with our current knowledge of the chiropractic adjustment effecting the thalamus, we can begin to offer an explanation of how the first historically reported chiropractic adjustment by D.D. Palmer helped Harvey Lilard regain his hearing.
CHIROPRACTIC ADJUSTMENTS REDUCES PAIN IN MULTIPLE REGIONS DUE TO LOCAL AND CNS STIMULATION
Mohammadian, Gonsalves, Tsai, Hummel, and Carpenter (2004) investigated “the hypoalgesic effects of a single SMT on acute inflammatory reactions and pain induced by capsaicin [hot pepper extract]. These effects were assessed by measuring both sensory (allodynia [central nervous system pain], hyperalgesia, spontaneous pain intensity) and local vascular parameters (blood flow)” (p. 382). They reported “As expected, topical capsaicin induced primary hyperalgesia in the application area and secondary hyperalgesia outside that area. While the local vascular parameter blood flow was not affected by a single SMT [spinal manual therapy], the results indicated that sensory parameters (spontaneous pain perception and areas of both secondary hyperalgesia and allodynia) were significantly altered after spinal manipulation compared with N-SMT [non-spinal manipulative therapy]. These results clearly demonstrated that in contrast to the N-SMT condition, a single spinal manipulation triggered hypoalgesic effects” (Mohammadian et al., 2004, p. 385).
“In the present study, local blood flow was not affected by a single SMT. However, significant changes were observed on sensory parameters, supporting the hypothesis of centrally mediated effects of a single SMT. It is well known that secondary hyperalgesia appears to be due to central sensitization of the spinal dorsal horn neurons,while primary hyperalgesia is caused by nociceptor sensitization. It has also been discussed that mechanisms underlying allodynia are centrally mediated.Our findings also confirm the view that the hypoalgesic effects of a single SMT might be due to central modulation. These effects could also be explained as a result of a stress reaction caused by spinal manipulation treatment…Other studies discussed thatspinal manipulation [chiropractic spinal adjustments] stimulates mechanoreceptors of the spinal joints, resulting in afferent discharges and subsequently causing inhibitory reactions on the dorsal horn neurons.Vicenzino et al. demonstrated also a strong correlation between hypoalgesic and sympathoexcitatory effects, suggesting that a central control mechanism might be activated by manipulative therapy… previous studies as well as the present investigation…indicate that hypoalgesic effects of spinal manipulation are more likely mediated through central modulation” (Mohammadian et al., 2004, p. 386). This study suggests that the chiropractic spinal adjustment affects the nociceptors and the mechanoreceptors at the joint level causing central modulation of an effect at the cord and/or brain level(s) and pain reductions in multiple areas as a result.
CHIROPRACTIC ADJUSTMENTS CREATE HIGHER FUNCTION IN CORTICAL REGIONS
Gay, Robinson, George, Perlstein, and Bishop (2014) reported, “With the evidence supporting efficacy of MT [manual therapy or chiropractic spinal adjustments] to reduce pain intensity and pain sensitivity, it is reasonable to assume that the underlying therapeutic effect of MT is likely to include a higher cortical component” (p. 615). It is in this place in particular that chiropractic must lead in both clinical application and academic processes such as formal continuing education lectures and research.
In the study conducted by Gay et al. (2014), “…pain-free volunteers processed thermal stimuli applied to the hand before and after thoracic spinal manipulation (a form of MT). What they found was that after thoracic manipulation, several brain regions demonstrated a reduction in peak BOLD [blood-oxygen-level–dependent] activity. Those regions included the cingulate, insular, motor, amygdala and somatosensory cortices, and the PAG [periaqueductal gray regions]” (p. 615). In other words, thoracic adjustments produced direct and measureable effects on the central nervous system across multiple regions, which in the case of the responsible for the processing of emotion (cingulate cortex, aka limbic cortex) are regarding the insular cortex which also responsible for regulating emotion as well has homeostasis. The motor cortex is involved in the planning and execution of voluntary movements, the amygdala’s primary function is memory and decision making (also part of the limbic system), the somatosensory cortex is involved in processing the sense of touch (remember the homunculus) and, finally, the periaqueductal gray is responsible for descending pain modulation (the brain regulating the processing of painful stimuli).