Neuroplasticity is the capacity of the nervous system to change its chemistry, structure, and function in response to intrinsic or extrinsic stimuli.1 Neuroplastic mechanisms are activated by environmental, behavioral, or neural processes, and by disease; they underpin the motor and cognitive learning associated with physical therapy or exercise. Neuroplasticity can lead to positive or negative changes in function, which are referred to as adaptive and maladaptive neuroplasticity, respectively. In their roles as clinicians and as scientists, physical therapists and other rehabilitation professionals harness neuroplasticity using evidence-based interventions to maintain or enhance functional performance in individuals with neurological disorders. There is still much to learn about the optimal interventions and parameters of dose and intensity necessary to achieve adaptive neuroplastic changes.
Beyond questions related to dose and intensity, more information is needed regarding the degree to which factors such as past experiences, age, sex, genetics, and the presence of a neurological disorder affects capacity for neuroplastic change. In addition, it is likely that these factors interact with each other, making it even harder to understand their influence on neuroplastic change. Improved measures for assessment of neuroplasticity in humans are needed, such as biomarkers (including movement-related biomarkers) for diagnosing disorders, and predicting and monitoring treatment effectiveness. Greater knowledge of effective rehabilitation and exercise interventions that drive adaptive neuroplasticity, and are tailored to each person's unique characteristics, will improve patient outcomes. The idea for this special issue was born out of a desire to advance understanding of the mechanisms driving functional change.
Two studies in this special issue use a newer neuroimaging method called functional near-infrared spectroscopy to measure cortical activity during dual-task walking.2,3 Impaired dual-task walking is common in neurological populations and can interfere with the ability to perform daily life activities. Hoppes et al2 examine frontal lobe activation patterns in individuals with and without visual vertigo during dual-task walking. The differences in cortical activation patterns identified increase our understanding of possible mechanisms underlying decrements in dual-task performance in individuals with vestibular disorders, and may be useful for diagnosis, and for predicting or determining functional recovery in this population. Stuart and Mancini3 investigate how open and closed-loop tactile cueing influences prefrontal cortex activity during single- and dual-task walking and turning in individuals with Parkinson disease. Tactile cues delivered to the feet in an open-loop (continuous rhythmic stimuli) or closed-loop (intermittent stimuli based on an individual's movement) mode are associated with improved gait and turning performance, and it is hypothesized that attention arising from the prefrontal cortex may underlie these cueing effects.4 Their findings of unchanged prefrontal cortex activity are unexpected, and raise additional questions regarding the role of the prefrontal cortex during gait.
Rehabilitation approaches such as task-oriented training that emphasize high repetition and challenge have been shown to facilitate recovery of mobility and function in neurological populations, but responses are varied and residual deficits often remain.5,6 There is still much to be learned about how to deliver the best interventions to optimize nervous system adaptive neuroplasticity and learning that ultimately lead to optimal functional recovery. In a proof-of-principle case series article in this special issue, Peters et al7 explore whether deficits in motor planning of stepping can be reduced by physical therapy focused on fast stepping retraining, or by conventional therapy focused on balance and mobility training, in individuals with subacute stroke. Both interventions altered electroencephalogic measures indicative of motor planning duration and amplitude of stepping; furthermore, duration changes for all participants were in the direction of those acquired from healthy adult values. These findings suggest that physical therapy may be able to drive neuroplasticity to improve initiation of stepping in individuals after stroke.
A growing body of human and animal evidence supports that aerobic exercise promotes neuroplasticity and functional recovery in many neurological disorders.1 Chaves et al8 utilized transcranial magnetic stimulation to examine changes in brain excitability measured in the upper extremity following a 40-minute bout of aerobic exercise (ie, body weight-supported treadmill walking) in individuals with progressive multiple sclerosis requiring devices for walking. Improvements in brain excitability were found following the aerobic exercise, which suggest that the capacity for neuroplasticity exists in this population. Participants' responses to the exercise were greater in those with higher cardiorespiratory fitness and less body fat. The authors discuss that maintaining an active lifestyle and participating in aerobic exercise may be beneficial for improving brain health and neuroplasticity in people with progressive multiple sclerosis.
Finally, for the first time Vive et al9 translate to the clinical setting the enriched environment model used in laboratory-based animal studies. Evidence from preclinical studies suggests that combinational therapies such as enriched environments, which take advantage of multiple mechanisms underlying neuroplasticity, may promote greater functional recovery than a single therapy.10 The researchers examine the effects of a high-dose enriched task-specific therapy, which combines physical therapy with social and cognitive stimulation on motor recovery in individuals with chronic stroke. Their findings demonstrate that the enriched task-specific therapy intervention is feasible, and suggest that it may be beneficial for repair and recovery long after a stroke.
The articles in this issue provide new insights to improve our understanding of adaptive neuroplastic changes in nervous system activity resulting from neurological disorders or following exercise interventions. Evidence regarding benefits of physical therapy and exercise interventions to promote motor and cognitive function across the lifespan and in the presence of neurological pathology may motivate individuals to adapt and adhere to healthier lifestyles.1 Physical therapists and rehabilitation professionals can use the evolving neuroplasticity research to assist with decision-making regarding individualized therapy goals, and the selection and monitoring of therapeutic interventions to best achieve compliance and goal attainment. Collaborations between rehabilitation clinicians and researchers will enhance and hasten the translation of neuroplasticity research into effective clinical therapies. In the end, these efforts will certainly lead us to improved interventions that help to restore function and health to our patients.
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