Since the inception of chiropractic, patients have reported improvements in areas of nervous system function following chiropractic adjustments of their spine. A spinal adjustment is a very quick thrust, delivered to an area of the spine in order to restore spinal and nervous system function. In the past ten years researchers have objectively demonstrated that spinal adjustments can change aspects of nervous system function including muscle reflexes, reaction time and the speed at which the brain processes information. 

A very exciting new area of chiropractic research is being conducted by a group of researchers at the University of Auckland in New Zealand. The project is lead by Dr. Bernadette Murphy, who is both a chiropractor and a human neurophysiologist. She is collaborating with colleagues in the Human Motor Control Laboratory, led by Dr. Winston Byblow. These researchers think that some of the changes in nervous system function reported by patients receiving chiropractic adjustments may be partly explainable by a process called neural plasticity. Scientists now understand that when the nervous system is subjected to unaccustomed inputs, changes can occur in the way the system processes all subsequent inputs. This ability of the nervous system to change the way it responds has been termed “neural plasticity”. These researchers have been able to show that neural plasticity partially explains how people can recover function after damage to the nervous system such as stroke. They are now applying their combined research expertise to investigate whether neural plasticity might occur when areas in the spine are not functioning properly, and whether spinal adjustments might, in fact, be able to reverse these changes. 

In the past ten years, two techniques have been developed to a level enabling the study of neural plasticity in human subjects. One of these techniques, somatosensory evoked potentials (SEPs), involves the measurement of spinal cord and brainwave peaks occurring in response to sensory inputs. By measuring how these brain waves are altered before and after spinal adjustments, it may be possible to understand whether neural plasticity occurs as a result of joint dysfunction. The second technique is called transcranial magnetic stimulation (TMS). TMS is a safe, non-invasive way of stimulating the motor area of the brain that controls movement. A magnetic coil causes a small excitation of the nervous system cells that control output to specific muscles. TMS allows us to measure changes in motor processing that may result from altered input from dysfunctional joints, and how that motor processing is changed following adjustments to the spine. 

Previously, the Auckland researchers have been able to show that adjustments to the cervical spine can change both the sensory processing of input from nerves in the hand and the output of the brain to muscles in the hand. Other researchers have previously demonstrated that plastic changes in neural processing occur in the brain in patients with carpal tunnel syndrome. The Auckland group has also shown that if input from a nerve in the arm is temporarily blocked with local anaesthetic, the output to muscles supplied from a different nerve is changed is changed, even though this nerve has not been blocked. These findings suggest that when the balance of inputs from the nervous system is altered, it changes the way the spinal cord and brain process all subsequent sensory input. These findings may be fundamental to understanding why the vertebral subluxation complex leads to nervous system disturbances that appear to be reversible. When a joint is not functioning properly, it alters the input from sensory receptors in the joint capsule and the muscles that move that joint. 

This altered input may lead to similar alterations in neural processing as observed in the patients with carpal tunnel syndrome or during nerve block with local anaesthetic. If neural plasticity is occurring as a result of “vertebral subluxations”, then spinal adjustments, by restoring normal inputs to the nervous system, will allow the spinal cord and brain to process incoming information in a more coherent way. This would then explain in whole, or in part, some of the improvements in nervous system functioning that have been previously documented following spinal adjustments. 

In order to study the way in which spinal adjustments were able to alter the output from the brain to the forearm muscles, the Auckland group are now making use of a new technique called “paired pulse magnetic stimulation”. By using two magnetic pulses a fraction of a second apart, the degree to which the output to a given muscle is “switched off’ or “switched on” can be measured. This technique provides a sensitive way of measuring markers of sensorimotor integration where sensory inputs to the central nervous system are modified (e.g. spinal adjustments). Changes to the levels of these markers are expected to reflect changes in the way the brain integrates the input from the muscles and joints in the neck and subsequently changes its motor output. By studying how altering the input from the neck to the brain can alter the output of the brain to the arm muscles, the researchers hope to better understand how chiropractic works. Ultimately this type of basic science research may help us understand how chiropractic is able to help improve strength, co-ordination, posture and balance.

Grant Value: $30,000
Chief Investigator: Dr Bernadette Murphy – University of Auckland
Status: Complete

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