J Electromyogr Kinesiol. 2012 (Oct); 22 (5): 768–776 ~ FULL TEXT
Heidi Haavik, Bernadette Murphy
New Zealand College of Chiropractic,
Auckland, New Zealand.
This review provides an overview of some of the growing body of research on the effects of spinal manipulation on sensory processing, motor output, functional performance and sensorimotor integration. It describes a body of work using somatosensory evoked potentials (SEPs), transcranial magnetic nerve stimulation, and electromyographic techniques to demonstrate neurophysiological changes following spinal manipulation. This work contributes to the understanding of how an initial episode(s) of back or neck pain may lead to ongoing changes in input from the spine which over time lead to altered sensorimotor integration of input from the spine and limbs.
From the Full-Text Article:
Over the past 15 years our research group has conducted a variety
of human experiments that have added to our understanding of
the central neural plastic effects of manual spinal manipulation
(Haavik and Murphy, 2011; Haavik-Taylor and Murphy, 2007a,b,
2008, 2010c; Haavik-Taylor et al., 2010; Marshall and Murphy,
2006). Spinal manipulation is used therapeutically by a number
of health professionals, all of whom have different terminology
for the ‘‘entity’’ that they manipulate. This ‘‘entity’’ which generally
describes areas of muscle tightness, tenderness and restricted
movement may be called a ‘‘vertebral (spinal) lesion’’ by physical
medicine specialists or physiotherapists, ‘‘somatic dysfunction’’
or ‘‘spinal lesion’’ by osteopaths, and ‘‘vertebral subluxation’’ or
‘‘spinal fixation’’ by chiropractors (Leach, 1986). For the purposes
of this article, the ‘‘manipulable lesion’’ will be referred to as an
area of spinal dysfunction or joint dysfunction. Joint dysfunction
as discussed in the literature ranges from experimentally induced
joint effusion (Shakespeare et al., 1985), pathological joint disease
such as osteoarthritis (O’Connor et al., 1993) as well as the more
subtle functional alterations that are commonly treated by manipulative
therapists (Suter et al., 1999, 2000).
Based on our research findings we have proposed that areas
of spinal dysfunction, represent a state of altered afferent input
which may be responsible for ongoing central plastic changes
(Haavik-Taylor et al., 2010; Haavik-Taylor and Murphy, 2007c).
Furthermorewe have proposed a potential mechanism which could
explain how high-velocity, low-amplitude spinal manipulation,
also known as spinal adjustments, improve function and reduce
symptoms. We have proposed that altered afferent feedback from
an area of spinal dysfunction alters the afferent ‘‘milieu’’ into which
subsequent afferent feedback from the spine and limbs is received
and processed, thus leading to altered sensorimotor integration
(SMI) of the afferent input, which is then normalized by highvelocity,
low-amplitude manipulation (Haavik-Taylor et al., 2010;
Haavik-Taylor and Murphy, 2007c). For a pictorial depiction of this
hypothesis, see Figure 1.
This article will provide an overview of some of the growing
body of research on the effects of spinal manipulation on sensory
processing, motor output, functional performance and sensorimotor
integration. This body of work contributes to our understanding
of how an initial episode(s) of back or neck pain may lead to ongoing
changes in input from the spine which over time lead to altered
sensorimotor integration of input from the spine and limbs.
Increasing this understanding may provide a neurophysiological
explanation for some of the beneficial clinical effects reported by
chiropractors and other manipulative therapists in day to day practice.
Chronic musculoskeletal pain affects the lives of millions of
individuals and places a great burden on health care systems in
the western world. Some of the research discussed in this review
has the potential to identify objective neurophysiological markers
which may be able to predict which patients will respond best to
spinal manipulative treatment and/or whether a patient has had
a sufficient amount of treatment to normalize neurophysiological
markers of disordered sensorimotor integration. The relationship
between the development and maintenance of chronic musculoskeletal
pain and neural markers of altered function is a promising
area in need of further research.
Altered sensorimotor processing following spinal manipulation
Several studies utilizing somatosensory evoked potentials
(SEPs) (Haavik-Taylor and Murphy, 2007c, 2010c; Haavik-Taylor
et al., 2010) have shown that manipulation of areas of joint dysfunction
in the cervical spine can alter somatosensory processing
and early sensorimotor integration of input from the upper limb.
These studies have shown alterations in the amplitude of the cortical
SEP peaks N20 (Haavik-Taylor and Murphy, 2007c) and N30
(Haavik-Taylor and Murphy, 2010c) following high-velocity, lowamplitude
cervical manipulation. The N20 SEP peak represents
the arrival of the afferent volley at the primary somatosensory cortex
(Desmedt and Cheron, 1980; Mauguiere, 1999; Nuwer et al.,
1994). Later SEP peaks are thought to be generated by the processing
of this somatosensory input (Cheron and Borenstein, 1991,
1992; Desmedt and Cheron, 1981; Desmedt et al., 1983; Kanovsky´
et al., 2003; Mauguiere et al., 1983; Rossini et al., 1989, 1987;
Waberski et al., 1999) and are therefore thought to reflect early
sensorimotor integration (Rossi et al., 2003).
One of these peaks,
the N30 SEP component is thought to have multiple generators.
Some authors suggest this peak is generated in the post-central
cortical regions (i.e. S1) (Allison et al., 1989a,b, 1991), while evidence
also suggests that this peak is related to a complex cortical
and subcortical loop linking the basal ganglia, thalamus, pre-motor
areas, and primary motor cortex (Cheron and Borenstein, 1991,
1992; Desmedt and Cheron, 1981; Desmedt et al., 1983; Kanovsky´
et al., 2003; Mauguiere et al., 1983; Rossini et al., 1989, 1987;
Waberski et al., 1999). Hence the N30 peak in particular is thought
to reflect early sensorimotor integration (Rossi et al., 2003). More
recently, Cebolla et al. have used swLORETA (standardized
weighted Low Resolution Brain Electromagnetic Tomography) taking
into account both phasic and oscillatory generators to determine
the neural generators of the N30 (Cebolla et al., 2011). They
have determined that the N30 is generated by network activity
in the motor, premotor and prefrontal cortex, adding further
weight to its role as a marker of neural processing relevant to sensorimotor
The results of these studies (Haavik-Taylor and Murphy, 2007c,
2010c; Haavik-Taylor et al., 2010) suggest that manipulation of
dysfunctional cervical segments can alter early sensory processing
and SMI of information from the upper limb. SMI is the process by
which the nervous system coordinates incoming sensory (afferent)
information from different parts of the body and integrates with
the motor system to control movement.
Over the past three decades it has become well established that
the human central nervous system (CNS) retains its ability to adapt
to its ever-changing environment, and that both increased (hyperafferentation)
and decreased (deafferentation) afferent input leads
to changes in CNS functioning (Bertolasi et al., 1998; Brasil-Neto
et al., 1993; Tinazzi et al., 1997). What has also become apparent
is that these plastic changes may occur in a manner that is subjectively
positive for the individual, such as with motor learning to
enable complex finger movement (e.g. playing the piano). This is
known as adaptive neuroplasticity. However, studies are also
showing that these plastic changes may occur in a manner that
has decidedly negative subjective outcomes for the individual,
known as maladaptive neural plastic changes.
There is a growing
body of literature that demonstrates maladaptive plastic changes
are present in a variety of pain conditions/syndromes and musculoskeletal
dysfunction (Falla, 2004; van Vliet and Heneghan, 2006),
and that such adaptive changes can occur remarkably fast following
an injury (Wall et al., 2002). This has lead various authors to
hypothesize that such maladaptive neuroplastic changes present
in long-term pain conditions rather than the actual pain itself is
responsible for the individual sufferer’s symptoms and functional
disturbances (Brumagne et al., 2000; Michaelson et al., 2003; Paulus
and Brumagne, 2008). In particular, changes in the way the CNS
processes proprioceptive information have been suggested as the
most important factor responsible for the clinical presentation of
neck pain sufferers (Paulus and Brumagne, 2008).
Numerous activities of daily living are dependent on appropriate
SMI. Interactions between sensory and motor systems allow
us to engage with our environment. It allows us to reach for and
grasp objects, detect and turn towards an auditory stimuli or respond
to perturbations from the environment in order to maintain
postural stability, balance and locomotion (Chen et al., 2009). SMI
involves strong feedback connections between different CNS structures
that are associated with numerous, and perhaps all, neuroanatomical
subsystems. These subsystems interconnect to form a
dynamic, multimodal, sensorimotor integrative system. This system
receives all afferent information from the environment. The
CNS utilizes all of these peripheral signals continuously to build
and maintain an internal reference frame (Lackner and DiZio,
2005; Sainsburg and Kalakanis, 1999).
This information is continuously
processed in relation to information it receives regarding the
voluntary intent of further movements, previous known estimations
about such movements and internal sensory feedback from
the actual movements when they take place. Continuous comparisons
and error adjustments take place, and over time so does motor
learning of frequent movements or actions. A breakdown
anywhere in these multimodal sensorimotor feedback loops has
the potential to greatly affect other interconnected neuroanatomical
subsystems, in either an adaptive or maladaptive manner.
Motor commands or motor intention (also known as ‘‘efference
copies’’) are for example known to interact with afferent signals to
generate sensation, and are known to contribute to joint position
sense (Smith et al., 2009). Under normal circumstances there is an
integration of intention, action and sensory feedback. Furthermore,
in a healthy state there is congruence between motor intention and
sensory experience (both proprioceptive and visual) when we for
example move a limb through space. Thus goal-directed action requires
ongoing monitoring of sensorimotor inputs to ensure that
motor outputs are congruent with current intentions as well as
the proprioceptive feedback from the actual movement.
This monitoring is automatic but can become conscious if there
is a mismatch between expected and realized sensorimotor states.
A recent study has demonstrated that providing a sensorimotor
conflict, i.e. providing unexpected visual feedback when moving
a limb (via hiding a moving limb and/or distorting visual feedback
of the movement of that limb) is sufficient to produce additional
somaesthetic disturbances, and exacerbation of pre-existing symptoms
in a group of fibromyalgia patients (McCabe et al., 2007). This
suggests that a conflict between our expected and realized sensorimotor
states can in some individuals produce or worsen pain sensations.
It is therefore possible that a mechanism by which spinal
manipulation relieves pain in patients is due to a central effect
by improving somatosensory integration processes. This theory is
however based on several assumptions that need to be verified
in future studies, such as whether a mis-match in expected and actual
sensory information can cause pain in healthy populations,
whether spinal dysfunction causes somaesthetic disturbances
and/or incongruence between motor intention and sensory experience
(both proprioceptive and/or visual), and whether this is improved
with spinal manipulation.
Discrepancies between expected and actual sensory information
can cause pain in healthy populations and this has been explored
in the laboratory setting (McCabe et al., 2005). Healthy
pain-free volunteers were asked to perform a series of bilateral
upper and lower limb movements whilst viewing these movements
in a mirror that created varied degrees of sensory–motor
conflict during the movements. They found that 66% of their
healthy pain-free volunteers reported at least one anomalous sensory
symptom at some stage in the protocol despite no peripheral
nociceptive input. Several of these volunteers reported parasthesia
sensations and mild aches or pain (McCabe et al., 2005), lending
support to the hypothesis that motor–sensory conflict can induce
pain and sensory disturbances in some normal individuals.
The importance of proprioception
Accurate proprioception is therefore an important component
of sensorimotor integration in the CNS. Proprioception includes
both joint position sense (JPS) and kinaesthesia (the sense of limb
movement in the absence of visual cues) (for review see Gilman,
2002). The main source of afferent information for JPS arises from
muscle spindles, however mechanoreceptors in joint capsules and
cutaneous tactile receptors may also contribute (for review see
Joint position sense has been extensively studied in the ankle, knee and hip joints (Adachi et al., 2007; Bennell
et al., 2005; Beynnon et al., 2002; Hazneci et al., 2005; Hopper
et al., 2003; Ishii et al., 1997; Karanjia and Ferguson, 1983; Larsen
et al., 2005; Marks, 1996; Okuda et al., 2006; Reider et al., 2003;
Ribeiro et al., 2007; Tsauo and Cheng, 2008),
particularly to investigate the effects of
reconstructive surgery (Adachi et al., 2007;
Hopper et al., 2003; Reider et al., 2003),
et al., 1991; Bennell et al., 2003; Marks, 1996),
joint bracing (for review
see Beynnon et al., 2002), and
various exercise or re-training
programs (Friemert et al., 2006; Hazneci et al., 2005;
Ribeiro et al., 2007; Tsauo and Cheng, 2008).
Recently there has also been an increased
focus in the literature on spinal JPS (Allison, 2003; Jull et
al., 2007; Learman et al., 2009; Strimpakos et al., 2006; Swinkels
and Dolan, 1998), however, much less research has looked at the
effect of the spine on limb JPS (Knox et al., 2006a,b; Knox and
Improved head repositioning accuracy has been demonstrated
by Palmgren et al. (2006) following chiropractic care, suggesting
that spinal manipulation can improve spinal proprioception. The
effects of improving spinal function on upper limb proprioception
has also recently been investigated in a group of 25 participants
with subclinical neck pain (SCNP) (i.e. reoccurring neck dysfunction
such as neck pain, ache and/or stiffness with or without a history
of known neck trauma) and 18 control participants (Haavik
and Murphy, 2011). This study demonstrated that the SCNP group
had reduced elbow joint position sense compared with those who
had no history of any neck complaints.
Furthermore, the study
showed that cervical spine manipulation of dysfunctional segments
improved the accuracy of the SCNP groups’ elbow joint position
sense (Haavik and Murphy, 2011). This suggests that cervical
dysfunction can impair the way that proprioceptive information
from the upper limb is processed. It also suggests that improving
spinal function with manipulative treatment leads to more appropriate
and accurate processing and integration of such proprioceptive
input. However, it is worth noting that this study does not
provide conclusive evidence that improving spinal ‘dysfunction’
was the precise cause of these observed effects.
In all of the cited studies by our group, spinal dysfunction was
‘quantified’ to some degree prior to and after each spinal manipulation
intervention by assessing for tenderness to palpation of the relevant
joints, manually palpating for restricted intersegmental range
of motion, assessing for palpable asymmetric intervertebral muscle
tension, and any abnormal or blocked joint play and end-feel of a
joint. All of these biomechanical characteristics are known clinical
indicators of spinal dysfunction (Fryer et al., 2004; Hestboek and
Leboeuf-Yde, 2000). These findings were documented pre and post
each spinal manipulation intervention. Improvements in segmental
function following spinal manipulation were also recorded for each
An important area for future research is to document more precise
biomechanical data pre and post spinal manipulation to explore
whether particular biomechanical characteristics of spinal
dysfunction are associated with poor proprioception. Similarly it
is necessary to explore whether particular biomechanical characteristics
of improved spinal function correlate with improved proprioceptive
processing. Furthermore, more precise reporting of
biomechanical characteristics of the manipulation may reveal correlations
between certain features of the manipulation and improved
proprioceptive processing. This should be explored in
In light of the above findings it is possible that the changes we
previously observed in the cortical N20 and N30 SEP peaks following
cervical spine manipulation (Haavik-Taylor and Murphy,
2007c, 2010c; Haavik-Taylor et al., 2010) reflect changes in the
way the research participant’s CNS was perceiving and processing
proprioceptive information from their stimulated upper limb. The
low intensity stimuli applied during SEP recordings which are just
above motor threshold, stimulate mainly large myelinated sensory
afferents such as 1a muscle afferents (Gandevia and Burke, 1988;
Gandevia et al., 1984).
There are numerous other studies that also implicate cervical
spine impairment in maladaptive sensorimotor integration, for
example affecting postural control and/or reduced JPS. This has
been observed with chronic neck pain (Falla, 2004; Michaelson
et al., 2003), neck muscle fatigue (Stapley et al., 2006), cervicobrachial
pain syndrome (Karlberg et al., 1995), cervical root compression
(Takayama et al., 2005a,b), and following whiplash
injury (Stapley et al., 2006; Sterling et al., 2003). Therefore, there
appears to be a considerable link between cervical function and
accurate proprioceptive processing. Although most of these previous
studies related to significant cervical injury or severe cervical
symptoms, one study has demonstrated that changes in head and
neck position in a group of participants without any history of neck
pain or injury led to reduced accuracy of elbow joint position sense
(Knox and Hodges, 2005). The authors of this study discussed how
accurate execution of movement depends on the ability of the CNS
to integrate somatosensory, vestibular, and visual information
regarding the position of the body (Knox and Hodges, 2005). They
argued that placing their subjects’ heads in full flexion and rotation
could have led to an overload of the computational capacity of the
CNS, thus resulting in increased JPS error (Knox and Hodges, 2005).
Altered somatosensory integration following spinal manipulation
A key component of typical SMI is early sensory integration of
afferent input. The interaction and integration of afferent inputs
from adjacent nerves at spinal, brainstem and cortical levels of
the somatosensory system can be evaluated with a particular SEP
protocol, i.e. by comparing spinal, brainstem and cortical SEP
amplitudes obtained after stimulating two peripheral nerves
simultaneously with the arithmetic sum of the SEP amplitudes obtained
after stimulating the same nerves individually. In healthy
subjects the dual input produces smaller SEP amplitudes compared
with SEP amplitudes that were produced from the same nerves
stimulated individually and arithmetically added together (Tinazzi
et al., 2000). This type of sensory filtering is the ability of an individual’s
CNS to suppress or attenuate the processing of multiple
afferent peripheral, mainly proprioceptive, inputs. It is thought to
reflect a type of ‘‘surround-like’’ inhibition, which in healthy individuals,
allows for the contrast between stimuli to remain high by
suppressing the processing of input from surrounding areas. In the
somatosensory system, such inhibition allows for the body to perceive
stimuli as separate and process them accordingly (Tinazzi
et al., 2000a,b).
This filtering process has been found to be altered in individuals
with neck pain, after repetitive muscular activities such as typing as
well as other musculoskeletal disorders such as dystonia (Haavik-
Taylor and Murphy, 2007a, 2010a,b, 2007c; Tinazzi et al., 2000).
Two studies, utilizing this particular dual peripheral nerve stimulation
SEP protocol both demonstrated that manipulating dysfunctional
cervical segments can increase the surround-like inhibition
of proprioceptive afferent input (Haavik-Taylor et al., 2010;
Haavik-Taylor and Murphy, 2010c). Figure 2 is reprinted from Haavik-
Taylor et al. (2010). It depicts a significant decrease in the N30
SEP peak when the median and ulnar nerve are stimulated simultaneously,
as compared with the arithmetic sum of the SEP amplitudes
obtained following stimulation of the two nerves
Earlier work by Tinazzi et al. (2000) found that dystonia patients
have a reduced ability to suppress the dual peripheral nerve
input. They argued that this reduced ability to suppress the dual
peripheral nerve input was evidence of inefficient integration,
and that this could give rise to abnormal motor output, which
might therefore contribute to the motor impairments present in
dystonia. The decreased SEP ratios following cervical spine manipulation
of dysfunctional spinal segments (Haavik-Taylor et al.,
2010; Haavik-Taylor and Murphy, 2010c), indicative of an enhanced
ability to filter sensory information, may therefore reflect
an improvement in early sensory integration of afferent input.
However, this assumes that a reduced ability to suppress dual
peripheral nerve input is always a negative finding, and that
increasing it reflects a positive or adaptive neuroplastic process,
neither of which is firmly established.
The ability of the CNS to gate sensory information is thought to
be important to maintain the internal representation of its current
posture or activity and to avoid undesirable reactions to external
or internal perturbations (Ivanenko et al., 2000; Paulus and
Brumagne, 2008). As Tinazzi et al. demonstrated that gating of sensory
information is distorted in patients with focal hand dystonia
(Tinazzi et al., 2000). Other groups have also demonstrated that
there is a shift in the gain of the sensory signals, i.e. a central
re-weighting of proprioceptive input, in patients with spasmodic
torticollis (Anastasopoulos et al., 2003) and low back pain patients
(Brumagne et al., 2004).
Altered motor control following spinal manipulation
Several studies utilizing transcranial magnetic stimulation (TMS)
(Haavik-Taylor and Murphy, 2007c, 2008) have also shown that
manipulating dysfunctional segments in the cervical spine can alter
sensorimotor integration of input from the upper limb. The TMS
experimental measures utilized in these studies, such as shortinterval-
intracortical-inhibition (SICI), short-interval-intracorticalfacilitation
(SICF) and the cortical silent period (CSP), are measures
of sensorimotor integration that are believed to reflect processing at
the level of the cortex (Cantello et al., 1992; Chen et al., 1999, 1998;
Di Lazzaro et al., 1998, 1999; Fisher et al., 2002; Hanajima et al.,
2002; Inghilleri et al., 1993; Kujirai et al., 1993; Kukowski and Haug,
1992; Tokimura et al., 1996; Ziemann et al., 1998).
These motor control
changes appear to occur in a muscle specific manner (Haavik-
Taylor and Murphy, 2008). Figures. 3 and 4 are reprinted from
Haavik-Taylor and Murphy (2008). Fig. 3 depicts a decrease in SICI
for the abductor pollicis brevis (APB) muscle following spinal
manipulation. No change was noted after the control intervention.
Fig. 4 depicts an increase in SICF for the APB muscle and a decrease
in SICF for the extensor indices proprios (EIP) muscle after the spinal
manipulation session. Again no change was observed after the control
intervention. The functional implications of these changes to
upper limb function need further exploration.
Improved neuromuscular performance with spinal manipulation
When performing bodily movements, like throwing a ball for
example, the central nervous system will activate a variety of postural
trunk muscles prior to any movement of the arm in order to
main postural stability during the throwing action. This process is
known as feed-forward activation (FFA). Individuals with chronic
low back pain are known to have delays in feedforward activation
(Hodges and Richardson, 1999; Hodges et al., 1996), which is
thought to influence postural stability. Early work by Murphy et
al. (1995) had demonstrated the ability of sacroiliac joint (SIJ)
manipulation to influence reflex excitability and her group sought
to determine if SIJ manipulation might also influence feedforward
activation. A study involving 90 healthy young males evaluated the
participants for delays in FFA in the transversus abdominis muscle
and internal obliques when undertaking rapid movements of the
upper limb (Marshall and Murphy, 2006).
Seventeen subjects had
a delay in FFA which was reproducible when retested 6 months later.
These subjects were examined by a chiropractor and were all
found to have dysfunction of the sacroiliac joint on the side of delayed
FFA. Following a single chiropractic manipulation of the dysfunctional
sacroiliac joint, the feed forward activation latency was
reduced by an average of 38% (Marshall and Murphy, 2006). This
study demonstrated an improvement in central nervous system
activation times of muscles associated with the stability of a specific
joint due to spinal manipulation. What is not known is
whether the improvement in FFA persisted beyond the time of
treatment. However, subsequent work by Marshall and Murphy
(2008) demonstrated that chronic low back pain participants treated
with manipulation and/or exercise, there was a continued
improvement in delayed FFA times at 1 year follow-up.
for the association between delayed muscle activation times and
impaired motor control is provided in a study by Radebold et al.
(2001). They measured the ‘‘on’’ and ‘‘off’’ times of 12 agonist
and antagonist trunk muscles during sudden trunk release movements
in different directions, as well as postural sway in individuals
with chronic back pain and controls. They found that chronic
low back pain patients have delayed muscle ‘‘on’’ and ‘‘off’’ times
and that these delays correlated significantly with impaired balance
performance with eyes closed. FFA times have also been
shown to correlate strongly with a patient’s self-rated disability
(Marshall and Murphy, 2010) indicating that these neuromuscular
measures may be useful markers of both treatment effects and potential
for chronicity in neck and back pain patients.
Motor impairments are present in chronic neck pain patients.
Impairment of deep cervical neck flexor activation and significant
postural disturbances during walking and standing have been demonstrated
in both insidious-onset and trauma-induced chronic neck
pain conditions (Alund et al., 1993; Branstrom et al., 2001; Jull et al.,
2004; Karlberg et al., 1995; Michaelson et al., 2003; Persson et al.,
1996; Rubin et al., 1995). Altered sensitivity of proprioceptors
within the neck muscles has been suggested to be related to the
postural (i.e. motor control) disturbances seen in these patients
(Michaelson et al., 2003; Persson et al., 1996). It has also been argued
that the degree to which proprioceptive input to the central
nervous system is disturbed, and even more importantly how the
CNS processes, interprets and transforms this afferent information
into motor commands, that determines the degree to which subjects
can successfully execute more challenging balance tasks
(Michaelson et al., 2003; Paulus and Brumagne, 2008).
It is therefore
possible that spinal manipulation in patients with sub-clinical
or more chronic neck pain is able to improve the central processing
of proprioceptive information, and that this is part of the mechanism
by which high-velocity, low-amplitude spinal manipulation
improve function and reduce chronicity and reoccurrence in these
patient populations. It is possible that the changes in cortical
somatosensory processing (Haavik-Taylor and Murphy, 2007c;
Zhu et al., 2000, 1993), sensorimotor integration (Haavik-Taylor
and Murphy, 2007c, 2008) and motor control (Haavik-Taylor and
Murphy, 2007b, 2008; Marshall and Murphy, 2006; Suter and
McMorland, 2002; Suter et al., 1999) that have been previously
documented following high-velocity, low-amplitude spinal manipulation
reflect changes in central processing of proprioceptive afferent
It is worth noting that the SEP recording protocol utilized in the
cited studies (Haavik-Taylor and Murphy, 2007c, 2010c; Haavik-
Taylor et al., 2010) cannot rule out spinal cord and/or brainstem
or subcortical changes. For example, more than 500 stimuli need
to be averaged for reliable far-field brainstem and subcortical SEP
peaks. SEP recordings also took several minutes to record and the
recordings did not commence until the electrode impedance was
re-checked after the cervical manipulations had been performed.
Short lived spinal and/or brainstem changes can therefore not be
ruled out either.
It is also worth noting that the cited studies (Haavik and
Murphy, 2011, 2007c, 2008, 2010a,c; Haavik-Taylor et al., 2010;
Marshall and Murphy, 2006) do not provide conclusive evidence
that the observed neuroplastic changes following spinal manipulation
are changes due to the correction of joint dysfunction.
Clinicians practicing manipulation assess, via palpation and observation,
that the area of spinal dysfunction has had its appropriate
range of movement restored following manipulation. It is tempting
to attribute the documented neurophysiological changes to this
restoration of appropriate movement (as we have proposed).
the observed neuroplastic changes could also merely be due
to the afferent barrage associated with the manipulative thrust.
Future studies should endeavour to address this question. We have
however cited one longer term study which showed that the FFA
time continued to improve up to one year after a 3 month period
of treatment with exercise and/or manipulation in a group of
chronic low back pain patients (Marshall and Murphy, 2008). This
suggests that some of these neurophysiological markers do indeed
have the capacity to improve following a period of successful care
even in a chronic back pain group.
Many of the studies discussed in this paper show that spinal
manipulation results in plastic changes in sensorimotor integration
within the central nervous system in human participants. Collectively
these studies provide evidence to support a central mechanism
of action for high-velocity, low-amplitude spinal manipulation. What
is not yet clear is the degree to which these changes correlate with
beneficial clinical outcomes. It is also not clear whether these changes
are due to the correction of spinal dysfunction, therefore normalizing
aberrant afferent input to the CNS, or whether they are merely
due to an afferent barrage associated with the manipulative thrust.
These questions remain to be answered and are the focus of our
ongoing research efforts.
The authors would like to acknowledge the following organizations
for support and funding over the past 15 years: Australian
Spinal Research Foundation, Hamblin Chiropractic Research Fund
Trust, University of Auckland Vice Chancellors Fund, New Zealand
Tertiary Education Commission Top Achievers Doctoral Scholarship,
Foundation for Chiropractic Education and Research, Natural
Science and Engineering Research Council of Canada, Canada Foundation
for Innovation, the University of Ontario Institute of Technology
and the New Zealand College of Chiropractic.
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Heidi Haavik is a chiropractor and a neurophysiologist
who has worked in the area of human neurophysiology
for the past ten years. She has utilized techniques such
as somatosensory evoked electroencephalography and
transcranial magnetic brain stimulation to investigate
the effects of chiropractic manipulation of dysfunctional
spinal segments on somatosensory processing,
sensorimotor integration and motor cortical output. Dr.
Haavik graduated from the New Zealand College of
Chiropractic in 1999, and was awarded her PhD degree
by the University of Auckland in 2008. She is currently
the Director of Research at the New Zealand College of
Chiropractic where she has established two human
neurophysiology research laboratories. Dr. Haavik is also an Adjunct Professor at the
University of Ontario, Institute of Technology in Oshawa, Canada and is a member of
the World Federation of Chiropractic’s Research Council. Dr. Haavik has received
numerous research awards and has published a number of papers in chiropractic and
neurophysiology journals. She has presented her work to both chiropractic and
neuroscience communities around Australasia, North America and Europe. She is on
the Editorial Board of the Journal of Manipulative and Physiological Therapeutics and
Journal of Chiropractic Education. She was named Chiropractor of the year in 2007 by
both the New Zealand Chiropractic Association and the New Zealand College of
Chiropractic Alumni Association.
Bernadette A. Murphy
Bernadette A. Murphy graduated from the Canadian
Memorial Chiropractic College in 1989 before moving
to New Zealand where she completed her MSc (1992)
and PhD (1998) in Human Neurophysiology at the
University of Auckland. She was a fulltime faculty
member in the Department of Sport and Exercise
Science from 1999 to 2007, where she established an
MSc in Exercise Rehabilitation. In January 2008, she
returned to Canada and took a position in the Faculty
of Health Sciences at the University of Ontario Institute
of Technology (UOIT). She is a Professor and
Director of Health Sciences and Kinesiology, and
heads the Human Neurophysiology and Rehabilitation
Laboratory. The overall theme of her research is neural adaptation in humans and
the role of physical interventions such as manipulation and exercise in aiding the
re-establishment of appropriate neuromuscular connections. She was the Recipient
of a $100,000 Vice-Chancellor’s Early Career Research Award at Auckland in 2002
which funded much of her initial work into neuromuscular alterations in chronic
low back pain, as well as several grants from the Australian Spinal Research
Foundation which enabled her to investigate disordered sensorimotor integration
in neck and back pain patients. Her current basic science research is funded by the
Natural Sciences and Engineering Research Council (NSERC) of Canada. She is on the
Editorial Board of ISRN Rehabilitation and the Journal of the Canadian Chiropractic
Association. She has supervised numerous Masters and PhD students and reviews
for several journals including Neuroimage, Journal of Neurophysiology, Spine, Clinical
Neurophysiology, Experimental Brain Research, JEK and JMPT.
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