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Physiotherapy Practice and Research 34 (2013) 1–8
DOI 10.3233/PPR-2012-0009
IOS Press
1
Discussion Paper
An update on brain plasticity for physical
therapists
Siobhan M. Schabruna,∗, Michael C. Riddingband Lucinda S. Chipchasea
aSchool of Health and Rehabilitation Science, University of Queensland, St Lucia, Brisbane, QLD, Australia
bThe Robinson Institute, School of Paediatrics and Reproductive Health, The University of Adelaide,
Adelaide, SA, Australia
Received 2 September 2012
Accepted 30 September 2012
Abstract. The understanding that the human brain is capable of structural and functional change throughout life has significant
implications for the future of physical therapy. Cortical plasticity impacts on many areas of physical therapy including clinical
practice, research and education. Although the principles of plasticity underpin developments in neurological physical therapy,
relevance to musculoskeletal physical therapy is still emerging. How will key areas of musculoskeletal physical therapy change
as our understanding of plasticity advances? If cortical plasticity can be harnessed, new plasticity-based therapies, that enhance
performance in healthy individuals and improve pain and function in patient populations, have the potential to become the
cornerstone of musculoskeletal physical therapy. In addition, common physical therapy techniques, such as electrical stimulation,
require reconsideration of their clinical efficacy and application in light of new discoveries in neuroscience. The aim of this
appraisal is to provide an update on brain plasticity for physical therapists in relation to clinical practice, research and education.
Keywords: Cortical plasticity, education, electrical stimulation, physical therapy, research, treatment
1. Introduction
The human brain is capable of profound structural
and functional change throughout life [1]. This ability,
now widely known as plasticity [2], is critical for skill
learning, memory and the recovery of function after
injury or illness [3]. Once considered possible only in
the very young, our understanding that brain connec-
tivity can change has provided an opportunity for a
paradigm shift in physical therapy. This paradigm has
underpinned major developments in neurological reha-
bilitation [4, 5]. However, the principles of plasticity
are also relevant to musculoskeletal physical thera-
pists where the potential for ‘peripheral’ conditions
∗Corresponding author: Dr. S.M. Schabrun, School of Health
and Rehabilitation Science, The University of Queensland, St
Lucia, QLD 4072, Australia. Tel.: +61 7 3365 4590; E-mail:
s.schabrun@uq.edu.au.
and manual, electrical and exercise treatments to affect
cortical plasticity is increasingly recognised. The pur-
pose of this appraisal is to provide an update on brain
plasticity for physical therapists in relation to clinical
practice, research and education.
1.1. Cortical plasticity
The clinical implications of a nervous system
that can change make this one of the most exciting
discoveries in the field of neuroscience. Cortical
plasticity has been defined as a structural or functional
change in the properties of neurons [6]. Plasticity can
be observed at all levels of the central nervous system
and occurs in response to many phenomena, including
environmental change, illness or injury, medication,
motor training and manipulation of afferent input
ISSN 2213-0683/13/$27.50 © IOS Press and the authors. All rights reserved
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2S.M. Schabrun et al. / An update on brain plasticity for physical therapists
[7–9]. In fact, afferent (sensory) input is known to be an
extremely powerful driver of plastic change [10–12].
This is highly relevant to physical therapy where
treatment techniques such as electrophysical agents,
motor retraining and manual therapy generate afferent
input with the potential to drive plasticity in the human
brain. Further, it is interesting to consider whether
many conditions encountered by physical therapists
may in fact, stem from altered afferent input caused
by inappropriate postures or injury. There is already
evidence for this proposition in chronic pain where
altered processing of afferent signals may underlie
chronicity by driving maladaptive plasticity in the
motor and sensory cortices [13, 14]. An understanding
of cortical plasticity and the role of afferent input is
therefore likely to assist therapists in the prevention
and treatment of these conditions in the future.
Cortical plasticity encompasses a range of mecha-
nisms including the awakening of previously unused
synaptic connections [15, 16], the growth of new
synapses [17] and changes in synaptic strength
[18]. Physical therapy interventions are most likely
to induce plasticity through alterations in synaptic
strength. This mechanism is typified by the adage
‘neurons that fire together, wire together’. First
postulated by Hebb, [19] if neuron A repeatedly
takes part in firing neuron B then the connection
between these neurons is strengthened. This process,
known as long-term potentiation (LTP), increases the
efficiency of the synaptic connection between cells
[18]. Conversely, the connection between two cells
can be weakened, leading to long-term depression
(LTD) of synaptic efficiency. LTP and LTD-like
changes are thought to be the primary short-term
mechanisms underlying plasticity in the human brain.
To understand the relationship between cortical
plasticity and motor learning two key points must
be highlighted. First, neurophysiological studies in
human subjects consider changes in cortical excitabil-
ity (often measured non-invasively using transcranial
magnetic stimulation) to be a marker of plasticity
(review see [20]). Thus, if excitatory (glutamergic)
synapses are the target, an increase in cortical excitabil-
ity may be considered to reflect LTP-like mechanisms
and a decrease to reflect LTD-like mechanisms. Sec-
ond, motor learning is associated with a rapid increase
in cortical excitability (and therefore LTP-like mech-
anisms [21]. It is reasonable to assume then, that
techniques which increase cortical excitability may
enhance learning in a rehabilitation context.
Plasticity can also manifest as changes in corti-
cal maps. The primary motor cortex is organised
topographically, a phenomenon frequently depicted
as the homunculus, with body parts represented
from medial (foot and leg representations) to lateral
(head and face representations) along the cerebral
surface [22]. Here, varying amounts of cortical terri-
tory, known as a representation or cortical map, are
devoted to muscles and movement patterns. How-
ever, cortical representations are capable of significant
reorganisation. One early example of reorganisation
demonstrated that the motor cortical representation
of the muscle controlling the ‘reading’ finger was
enlarged in blind individuals who were proficient
Braille readers when compared with less experienced
Braille readers [23]. Similar expansions in cortical ter-
ritory for finger and hand muscles have been reported
in elite string musicians [24] and skilled racquet play-
ers [25] when compared with control subjects. These
examples demonstrate the importance of intensive
practice in the induction of plasticity. However, cor-
tical reorganisation also occurs with inactivity of a
body part. For example, transient deafferentation of
the forearm and hand has been demonstrated to result
in expansion of the cortical territory of muscles prox-
imal to the block [26], presumably into the region
of the “dennervated” cortex. Similar findings have
been reported in amputees, where increased cortical
representations have been demonstrated for muscles
proximal and ipsilateral to the amputation [11].
Of relevance to physical therapists, the degree of
cortical reorganisation has been shown to correlate
with functional recovery following peripheral [10],
spinal [27] and cortical injuries [28]. For example,
cortical reorganisation in the primary motor cortex
occurs in association with functional recovery follow-
ing sub-cortical stroke [28]. This has led to the widely
held belief that cortical reorganisation contributes to
motor recovery and assists in compensating for last-
ing impairment, making it an attractive target for new
approaches to therapy.
Plasticity, while generally thought of as beneficial
or adaptive, can also be maladaptive. This is postu-
lated to contribute to the vicious cycle of pain, motor
impairment and reduced function considered to under-
lie many chronic musculoskeletal conditions. Flor and
colleagues [29] demonstrated a shift in the cortical rep-
resentation of the mouth towards that of the former
hand representation after amputation in those experi-
encing phantom limb pain. These same changes were
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S.M. Schabrun et al. / An update on brain plasticity for physical therapists 3
not present in individuals who did not experience phan-
tom limb pain. Similarly, cortical representations are
abnormally enlarged and overlapped in focal hand
dystonia [30–33] interfering with isolated movements
of the hand, and representations are shifted posteri-
orly in chronic low back pain [14]. Excitingly for
physical therapists, normalisation of cortical organi-
sation has been demonstrated to occur with targeted
electrical stimulation paradigms [30, 34] and motor
retraining [35–39]. Thus, techniques that prevent or
reverse maladaptive plasticity are equally as relevant
to the future of physical therapy practice as techniques
which enhance adaptive plasticity.
1.2. Considerations for clinical practice
In the domain of clinical practice, there are two key
areas where physical therapists need to focus atten-
tion. First, we must carefully consider the effect of
current therapies on cortical structures. Many physical
therapy treatments have been designed based on physi-
ological effects that have been demonstrated to occur in
peripheral and spinal structures. A case in point is elec-
trical stimulation (ES). Electrical stimulation is used
extensively by physical therapists to reduce pain and
improve motor function across a range of conditions
[40–42]. Yet, in basic science research, ES has been
used for many years as a repeatable form of afferent
input to drive plastic change [43]. Indeed in humans, it
is clear that ES produces effects on the cortex in addi-
tion to those in the periphery and spinal cord [43, 44].
Recent work has demonstrated that ES delivered at
intensities sufficient to produce a muscle contraction
(as in neuromuscular nerve stimulation) results in an
increase in excitability of the cortical representation of
the muscle stimulated. However, intensities at either
sensory or noxious thresholds reduces excitability [44].
These findings suggest that a therapist who applies ES
for pain relief at sensory intensities prior to motor
retraining may theoretically be reducing the brain’s
ability to learn. Although this premise is speculative,
it highlights the need for physical therapists to stay
abreast of basic science research. Further, it raises an
important question. Are physical therapists producing
detrimental or unwanted cortical effects during some
physical therapy applications?
Conversely, the ability of ES to induce cortical
effects opens up the tantalising prospect that phys-
ical therapists can use ES in novel ways to drive
beneficial plastic change and prevent or reverse the
development of maladaptive plasticity. In fact, neuro-
scientists have been using ES techniques in novel ways
and these are gaining momentum in the basic science
field. For example, non-associative ES involves the
application of electrical stimuli at motor intensity to
two hand muscles asynchronously. This approach has
been used to normalise maladaptive cortical plasticity
in focal hand dystonia by driving the cortical represen-
tations for two hand muscles further apart [30]. This
treatment is based on literature demonstrating that cor-
tical representations are abnormal in those with focal
hand dystonia [31, 32, 45]. This example highlights
the importance of understanding cortical mechanisms
in different pathologies if new treatments are to be
designed and implemented.
Second, novel applications for ES techniques are
currently being tested in the neuroscience field.
For example, transcranial direct current stimulation
(tDCS), an emerging brain stimulation technique, has
the potential to reduce pain and improve function in a
range of conditions [46]. Yet the application of direct
current to the human body is not new, with physi-
cal therapists using direct current in the periphery for
wound healing and iontophoresis since the early 1900’s
[47, 48]. When applied transcranially, depending on
the polarity of the active electrode (anodal or catho-
dal), cortical excitability can be enhanced or reduced
through alteration of resting membrane potential [49,
50]. Currently, tDCS is being tested as a treatment to
alter the resting state of the cortex by increasing or
decreasing cortical excitability and as an adjunct treat-
ment to increase the receptiveness of the brain to other
therapies. The latter, known as priming [51], should be
of considerable interest to physical therapists.
Priming the brain to reach an optimal state of
excitability presents innumerable opportunities for
physical therapy practice. One example of this
approach is the combination of tDCS and tran-
scutaneous electrical nerve stimulation (TENS)
in individuals with chronic neurogenic pain. The
rationale for combining tDCS with TENS is to
increase the receptiveness of the cortex to TENS
and to combine the cortical effects of tDCS with the
spinal and peripheral effects elicited by TENS. tDCS
combined with TENS for a period of 30 minutes
has been demonstrated to induce a greater reduction
(36.5%) in pain scores than tDCS alone (15.5%) or
sham stimulation [52]. Although this study failed
to include a TENS alone group, pain reductions
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4S.M. Schabrun et al. / An update on brain plasticity for physical therapists
obtained following TENS in other work suggests
that the combination of tDCS and TENS produces
superior decreases in pain scores [53, 54]. If tDCS can
successfully prime the brain, then there is potential for
it to be used with a range of interventions including
motor retraining, manual therapy and other forms of
afferent input. Although, evidence for priming is in
the early stages and tDCS is not yet approved for
clinical use, a vision of physical therapy where the
brain is primed to learn is no longer farfetched.
Finally, a greater understanding of cortical plas-
ticity may have benefits for the rehabilitation of
musculoskeletal conditions in other ways. Consider-
able research is emerging on the factors that affect
plastic change. These include time of day, attention,
gender, medication and frequency of treatment appli-
cation (review see [55]). For instance, increases in
cortical excitability have been shown to be greater later
in the day than in the morning [56, 57] and plasticity
protocols applied repeatedly at short intervals produce
greater and longer-lasting plastic changes [58] than
single applications or applications at longer intervals.
Importantly, behavioural relevance is a key aspect of
plastic change [59, 60]. This work suggests that when
the goal of therapy is to take advantage of the poten-
tial for plasticity, it may be more efficacious to apply
multiple goal-directed treatments spaced at intervals of
minutes, rather than days, and to schedule therapy ses-
sions for later in the day. Consideration of these factors
has the potential to alter the way therapists practice. It is
possible to envisage a time when single 20 minute ses-
sions spaced days or weeks apart become the exception
rather than the norm.
A key focus of physical therapists, particularly in
the field of low back pain, is to identify and sub-group
individuals based on factors that are likely to predict
response to treatment. Similarly, an individual’s
predisposition to plasticity may affect their response
to plasticity-based therapies. Although evidence in
this area is still gaining momentum, exercise, age
and genetic profile are factors likely to affect the
plasticity response (for review see [55]. For example,
individuals who regularly engage in aerobic activity
have a greater capacity for plastic change, enhancing
learning and memory than sedentary individuals [61,
62]. The magnitude of plasticity is also greater for
young and middle aged individuals than for those
aged over 60 years. In particular, some protocols
known to induce plasticity in younger individuals,
fail to do so in those aged over 60 years [63, 64].
An individual’s genetic profile is also a important
factor. Neurotrophins, particularly brain derived
neurotrophic factor (BDNF), play a role in altering
brain connectivity [65, 66]. Yet a large proportion of
the population have a polymorphism in the BDNF
gene that reduces their capacity for plastic change
[67, 68]. As plasticity-based therapies advance, new
sub-groups are likely to be developed based on factors
that influence an individual’s capacity for plasticity.
1.3. Considerations for research
Our understanding of cortical plasticity has begun
to infiltrate and guide physical therapy research. There
are several implications of this new understanding in
terms of research. First, translational research has been
considered traditionally as a unidirectional pipeline
from basic science to clinical application. In the mod-
ern healthcare setting, this ‘bench to bedside’ model
is outmoded and it is increasingly recognised that, to
be effective, the research pathway must be bidirec-
tional [69]. This means that clinical research at one
end of the pipeline must be informed by and con-
tinually evaluated in light of discoveries in the basic
sciences [70]. Similarly, basic science research must
be informed by and continually evaluated in light
of discoveries in the clinical sciences. A collabora-
tive model such as this has the potential to lead to a
more rapid uptake of novel ideas and translation of
these into efficacious clinical outcomes. Physical ther-
apists with their grounding in anatomy, physiology and
neuroscience have the potential to contribute to the
rapid translation of new discoveries in the neuroscience
field.
Second, the rapid development of new knowledge in
the neuroscience field means that we must be cautious
about the interpretation of clinical trials and system-
atic reviews. Again ES can be used as a case in point.
Results of randomised controlled trails and systematic
reviews of TENS as a treatment for acute [71] and
chronic pain [72] demonstrate conflicting or inconclu-
sive findings. However, the application of TENS in
these studies fails to consider the effect of ES on corti-
cal plasticity. Subtle changes in stimulus intensity can
rapidly reverse the effect of ES on the cortex from one
of excitation to one of depression [43, 44]. Additional
sources of bias, such as the addition of co-interventions
in TENS trials have also been highlighted [73]. There
is the real possibility that the combination of TENS
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S.M. Schabrun et al. / An update on brain plasticity for physical therapists 5
with other therapies or variation in stimulus intensi-
ties interferes with the plastic response reducing the
effectiveness of the TENS intervention.
A clinical example is the use of ES for pain relief
in the treatment of osteoarthritis of the knee [74].
ES at sensory intensities has been shown to reduce
cortical excitability [43, 44]. Thus, the application of
ES to the knee might in fact be producing undesirable
effects in the motor cortex, reducing excitability of
the corticomotor pathway to the quadriceps muscles,
thereby limiting clinical outcomes. Without a greater
understanding of the role of cortical plasticity in
pathologies and physical therapy treatments, care
must be taken when interpreting negative findings
in clinical trials and systematic reviews. Indeed,
inconclusive findings, as reported by many systematic
reviews, may not be due to the technique itself but
to our limited understanding of how to control for
desirable or undesirable effects on the cortex.
In an evidenced based climate where clinical tri-
als and systematic reviews are considered the most
important drivers of clinical practice, it is important
that physical therapists review and adopt evidence in
light of a critical appraisal of basic science concepts
and physiological mechanisms. A broader approach to
interpreting research is likely to serve the discipline of
physical therapy better than an approach limited to the
current EBP framework.
1.4. Considerations for education
In order to facilitate the translation of cortical plas-
ticity into physical therapy practice, new educational
strategies need to be developed. Most new graduate
physical therapists understand that brain connectiv-
ity can change. Yet the speed with which this field
is changing, particularly in relation to disease mech-
anisms and treatment options, means that entry level
students must be exposed to cutting-edge research as it
happens. This integration should start from day one in
physical therapy programs and ideas of how to progress
this learning throughout and beyond entry-level train-
ing are needed. Building greater links between research
(both clinical and basic science) and teaching in phys-
ical therapy education will help facilitate the transition
of knowledge.
A more integrated approach to physical therapy
education may also enhance the translation of plastic-
ity concepts into practice. Currently many entry level
programs separate teaching into core practice areas
such as neurological, cardiorespiratory and muscu-
loskeletal topics. Although practical, this model fails
to highlight the importance of the brain in conditions
which are not defined as neurological. For example, a
student in a musculoskeletal course reasoning through
a leg injury may be encouraged to consider spinal
or peripheral mechanisms but not the role of corti-
cal plasticity. Similarly, treatments such as ES used
for musculoskeletal treatments may only be applied in
relation to their peripheral and spinal effects without
considering their effect on the brain.
If plasticity based techniques become an integral
part of physical therapy practice in the future, phys-
ical therapy students must have a good understanding
of the plastic mechanisms present after illness and
injury. This will ensure that physical therapists are able
to adopt plasticity-based techniques and apply them
appropriately in clinical practice. For example, a con-
dition like focal hand dystonia, in which the brain is too
excitable, is likely to require a technique that reduces
cortical excitability. Conversely, conditions where the
brain is under active may require excitability enhanc-
ing techniques. Providing fundamental education and
training in this area now, will ensure that the phys-
ical therapists of the future are well placed to take
advantage of this novel field.
2. Conclusion
The plastic capabilities of the human brain have sig-
nificant relevance to musculoskeletal physical therapy.
Afferent input generated by ‘peripheral’ conditions and
in the form of exercise, manual therapy or electrical
stimulation is a powerful driver of plastic change. It
is essential that physical therapists consider the effects
of current therapies on the brain and contribute to the
development of new plasticity-based therapies capable
of enhanced performance, reduced pain and improved
recovery of function. Consideration and integration of
plasticity concepts into clinical practice, research and
education will ensure physical therapists stay abreast
of this rapidly advancing field.
Funding sources
SMS is supported by a Clinical Research Fellowship
(631612) and MCR by a Senior Research Fellowship
AUTHOR COPY
6S.M. Schabrun et al. / An update on brain plasticity for physical therapists
(519313) both from The National Health and Medical
Research Council of Australia. LSC is supported by a
University of Queensland Teaching Fellowship.
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