Consider, for example, that humans suffer with conditions associated with increased nerve activity. Pain is the best example. The great majority of afferent fibers innervating spinal joint tissues are group IV afferents, which typically function as nociceptors.1,2 Their activity dramatically increases with tissue,3,4 as does central nociceptive processing,5 and the outcome is pain.
One of the best-studied outcomes of spinal adjusting is the reduction of back pain, which suggests that the adjustment interferes with overactive nociceptive neurons. Reviews of the literature suggest that the adjustment stimulates afferent fibers that reduce nociceptive activity.4,5 So, should we say that the adjustment causes nociceptive nerve interference?
What About Visceral Symptoms?
It is not uncommon for DCs to report that patients with visceral symptoms improve after an adjustment. Review articles have discussed various mechanisms; the most likely cause of visceral symptoms is increased nociceptive input and associated increased suprasegmental, and perhaps, segmental autonomic activity.4,6 Accordingly, when an adjustment relieves a patient of visceral symptoms, should we say that the adjustment causes nociceptive and autonomic nerve interference?
What About Changes in Paraspinal Muscle Activity?
EMG activity was assessed in paraspinal muscles while pressure was applied to the spinous processes of painful and nonpainful spinal motion segments.7 A significant increase in bilateral EMG was found in the painful segment compared with the nonpainful segment. After an adjustment was applied to the painful motion segment, there was a significant reduction in EMG activity when pressure was again applied to the spinous process, suggesting that the adjustment may reduce nociceptive activity and related hyperactive muscle activity in a painful spinal motion segment. Should we conclude that the adjustment causes nerve interference in the sensory and motor systems?
In another study, EMG activity was assessed during quiet standing and during a complex movement (the golf swing) in a professional golfer with chronic low back pain. After a chiropractic adjustment, it was determined that there was a decrease in muscle activity during quiet standing after the completion of movement, during independent quiet standing, and during the golf swing. Should we conclude that the adjustment causes nerve interference to the motor system?
In still another study, the H-reflex was measured before and after massage and spinal adjustments, to determine if either intervention causes changes in motor neuron activity. Massage subjects exhibited no significant reduction in motoneuronal activity immediately following administration. Spinal manipulation produced a transient reduction of alpha motoneuronal excitability. Paraspinal and limb massage did not inhibit the motoneuron pool as measured immediately post-therapy. These findings support the supposition that spinal manipulation procedures lead to short-term inhibitory effects on motoneuron excitability to a greater magnitude than massage.9 Should we conclude that the adjustment causes a greater degree of nerve interference in the motor nervous system compared to massage? And should we also conclude that massage therapy is not as effective as a chiropractic adjustment, because massage does not cause nerve interference as effectively as an adjustment?
Problems With My Theory That the Adjustment Causes Nerve Interference
For those who might be misinterpreting what they have read thus far, I am not serious about using the term "nerve interference" in the fashion described above. I don't think we should say that the adjustment causes nerve interference, because the adjustment can have both inhibitory and excitatory responses. However, at the same time, there is no evidence or compelling reason to suggest that subluxations cause nerve interference and that the adjustment corrects nerve interference. The term "nerve interference" does not seem to apply to subluxation or post-adjustment neurologic changes.
One thing we can say for sure is that the adjustment stimulates somatic afferents. When adjusting a spine, we apply pressure through the skin and muscles, and then gap spinal joints; this process stimulates somatic afferents. If you were blindfolded, lying prone, and had your mid-dorsals adjusted, you would know it because the somatic afferentation would lead to cortical stimulation and the realization that your midthoracic spine was adjusted. This being said, no one knows exactly how, or to what extent, afferents are activated during an adjustment, and we don't know the details about the central effects of the adjustment. We have some ideas and reasonable hypotheses, as described earlier, but we don't for sure know about the precise mechanisms.
It is quite possible that the adjustment stimulates somatic afferents (group I-IV fibers),10 resulting in both inhibitory and excitatory effects in the central nervous system. My suspicion is that reduced movement and inflammation in a spinal motion segment lead to reduced mechanoreception and increased nociception, which may be normalized or modulated by the adjustment.4
Pickar recently reviewed the literature, and not surprisingly, it is not clear what occurs in the CNS after an adjustment. There are likely to be both excitatory and inhibitory reflex changes in the somatic and autonomic nervous systems.11 In this regard, consider that by measuring the H-reflex, Dishman determined that the adjustment inhibits segmental outflow of motoneurons.9 However, when motor neuron pool excitability was measured directly by central corticospinal activation with transcranial magnetic stimulation techniques, a transient but significant facilitation occurred as a consequence of spinal manipulation. Thus, a basic neurophysiologic response to spinal manipulation is central motor facilitation.12 Clearly, the adjustment has both central inhibitory and excitatory effects.
Summary
The term "nerve interference" really does not fit well when used in its classic sense, or in the manner I suggested earlier. This is because dysfunction of spinal joints, or subluxation, is likely to lead to inhibition and excitation of various pools of central neurons, and the adjustment is likely to modulate such inhibitory/excitatory activity.
The best hypothesis we have working for us is the idea that the adjustment activates somatic afferents, and such stimulation results in modulation of central nociceptive processes and central modulation of sensory-motor and autonomic processes. However, we do not know the degree of such changes, their duration, or exactly how they operate in the clinical setting.
What this basically means is that a trial of adjustments may provide relief for patients with back pain, headaches, sensory-motor disturbances, and perhaps certain visceral symptoms. As long as no red flags are present, a trial of adjustments is not an unreasonable choice, which means that many people should be visiting the local chiropractor to see how an adjustment can favorably modulate their nervous systems.
References
- Leach RA, Pickar JG. Segmental dysfunction hypothesis: joint and muscle pathology and facilitation. In Leach RA. Ed. The Chiropractic Theories: A Textbook of Scientific Research. Baltimore: Lippincott Williams & Wilkins; 2004:137-205.
- Mense S, Simmons DG. Muscle Pain: Understanding Its Nature, Diagnosis and Treatment. Philadelphia: Lippincott Williams & Wilkins; 2001:26-30.
- Seaman DR, Cleveland C. Spinal pain syndromes: nociceptive, neuropathic, and psychologic mechanisms. J Manip Physio Ther 1999;22:458-72.
- Seaman DR, Winterstein JF. Dysafferentation, a novel term to describe the neuropathophysiological effects of joint complex dysfunction: a look at likely mechanisms of symptom generation. J Manip Physiol Ther 1998;21:267-80.
- Boal RW, Gillette RG. Central neuronal plasticity, low back pain, and spinal manipulative therapy. J Manip Physiol Ther 2004;27:314-26.
- Nansel D, Szlazak M. Somatic dysfunction and the phenomenon of visceral disease simulation: a probable explanation for the apparent effectiveness of somatic therapy in patients presumed to be suffering from true visceral disease. J Manip Physiol Ther 1995;18(6):379-97.
- Lehman GJ, Vernon H, McGill SM. Effects of a mechanical pain stimulus on erector spinae activity before and after a spinal manipulation in patients with back pain: a preliminary investigation. J Manip Physiol Ther 2001;24(6):402-6.
- Lehman GJ, McGill SM.The influence of a chiropractic manipulation on lumbar kinematics and electromyography during simple and complex tasks: a case study. J Manip Physiol Ther Nov-Dec 1999;22(9):576-81.
- Dishman JD, Bulbulian R. Comparison of effects of spinal manipulation and massage on motoneuron excitability. Electromyogr Clin Neurophysiol 2001;41:97-106.
- Gillette RG. A speculative argument for the coactivation of diverse somatic receptor populations by forceful chiropractic adjustments. Man Med 1987;3:1-14.
- Pickar JG. Neurophysiological effects of spinal manipulation. The Spine J 2002;2:357-71.
- Dishman JD, Ball KA, Burke J. First Prize: Central motor excitability changes after spinal manipulation: a transcranial magnetic stimulation study. J Manip Physiol Ther 2002;25:1-9.
David Seaman, DC, MS, DABCN
Port Orange, Florida
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