Elsevier

Journal of Communication Disorders

Volume 44, Issue 5, September–October 2011, Pages 521-528
Journal of Communication Disorders

Neural plasticity and neurorehabilitation: Teaching the new brain old tricks

https://doi.org/10.1016/j.jcomdis.2011.04.006Get rights and content

Abstract

Following brain injury or disease there are widespread biochemical, anatomical and physiological changes that result in what might be considered a new, very different brain. This adapted brain is forced to reacquire behaviors lost as a result of the injury or disease and relies on neural plasticity within the residual neural circuits. The same fundamental neural and behavioral signals driving plasticity during learning in the intact brain are engaged during relearning in the damaged/diseased brain. The field of neurorehabilitation is now beginning to capitalize on this body of work to develop neurobiologically informed therapies focused on key behavioral and neural signals driving neural plasticity. Further, how neural plasticity may act to drive different neural strategies underlying functional improvement after brain injury is being revealed. The understanding of the relationship between these different neural strategies, mechanisms of neural plasticity, and changes in behavior may facilitate the development of novel, more effective rehabilitation interventions for treating brain injury and disease.

Learning outcomes: Readers will be able to: (a) define neural plasticity, (b) understand how learning in the intact and damaged brain can drive neural plasticity, (c) identify the three basic neural strategies mediating functional improvement, and (d) understand how adjuvant therapies have the potential to upregulate plasticity and enhance functional recovery.

Highlights

Neural plasticity is the neurobiological mechanism supporting functional improvement after brain injury. ► The brain uses different neural strategies to facilitate functional improvement after brain injury. ► Understanding the factors driving neural plasticity may facilitate the development of better therapies.

Introduction

Medical advances have increased the average life expectancy in North America by over 30 years in the last century. Increased survival from traumatic brain injury, and an increase in the number of individuals suffering from age related neurological impairment, has significantly increased the number of individuals receiving neurorehabilitation. Unfortunately, this in turn has highlighted the relatively slow progress in neurorehabilitation as compared to other medical disciplines such as cardiology and immunology. Most major medical advances can be traced back to basic science research that first determined the fundamental properties of the dysfunctional biological system and then developed an appropriate treatment. The biological system and causes of dysfunction that neurorehabilitation deals with are far more complicated and diverse than those associated with heart disease or influenza. The brain is the most complex biological system on the planet and the sources of functional impairment are many ranging from the sudden loss of tissue due to a stroke or traumatic injury to the decades long neurodegeneration associated with Parkinson's or Alzheimer's disease. A second issue is the historical lack of interaction between basic and clinical rehabilitation scientists. In academic settings, physical therapy, occupational therapy, and physical medicine departments are isolated from basic science departments such as neuroscience, biochemistry or physiology. They publish in different scientific journals, attend different scientific conferences, and speak different scientific languages. This has hindered our ability to develop effective, clinically relevant, interventions that are informed by basic neurobiology. All of this has, however, begun to change over the last several years. This is not because basic science has suddenly discovered some critical aspect of brain function that can be immediately translated into treatment. Rather, basic science disciplines such as neuroscience are simply beginning to more fully characterize a fundamental property of the brain that was recognized over a hundred years ago: the capacity for neurons to structurally and functionally adapt in order to reorganize neural circuits, i.e. the capacity for neural plasticity.

The purpose of the present review is to describe some of the key issues related to how understanding neural plasticity might guide the development of more effective rehabilitation interventions. It is predicated on the hypothesis that functional improvement is in part related to the capacity for neural plasticity within residual neural circuits. Such plasticity affords the opportunity to train the new brain to perform old functions lost due to injury or disease.

Section snippets

Functional improvement after brain injury is a relearning process

Restoring function after brain injury or disease is not trivial and although neuroscience has made major advances, we are far from understanding brain circuitry at the level needed to place new neurons and synapses in just the right places to restore lost function after damage. One way to approach the problem is by recognizing that functional improvement after injury is a relearning process. During therapy, patients are guided through practice to try and re-acquire the ability to produce

Learning-dependent neural plasticity

Evidence for learning dependent neural plasticity can be found in every animal species across virtually every behavioral modality. To review this literature is beyond the scope of the paper. However, much of what rehabilitation therapists deal with involves motor training to re-establish lost motor abilities and, as such, this review will focus on plasticity within the motor system associated with motor training. Virtually all of our daily behaviors, from speaking to tying our shoes, involve

Recovery versus compensation

Although this paper presents neurorehabilitation as a relearning process there is one clear difference between learning in the intact brain and relearning in the damaged brain. Specifically, unlike in normal learning conditions, rehabilitation can take advantage of previously learned behaviors that may still exist within the residual neural circuits of the damaged brain. These behaviors may have been masked due to some neurobiological phenomenon such as inflammation, edema, or increased neural

Neural strategies for motor improvement after brain injury

Neurorehabilitation therapists face several variables that can contribute to the capacity for functional improvement when treating neurological injury or disease. These include patient health status, age, lifestyle, and time after injury in addition to the nature and locus/extent of the brain injury. All of these factors compound to create a brain that is very different from the “normal” brain and an incredibly diverse range of impairments even within the same injury domain. This leads to

Clinical implications

The goal of this research area is of course to gain sufficient knowledge of the key behavioral and neural signals that drive neural plasticity in order to develop patient specific therapies that increase the opportunity for functional improvement. Neuroscience has identified several such signals and treatments such as deep brain stimulation for Parkinson's and Constraint-induced movement therapy in stroke have become prevalent in clinics. Preclinical studies in animals have also identified

Why should therapists care about neural plasticity?

Most training programs for physical therapy, occupational therapy, or speech language pathology focus primarily on behavioral interventions that may have the greatest impact on enhancing functional outcome. So why should therapists need to know at all about neural plasticity? There are several answers to this question. First, measures of neural plasticity provide a surrogate marker for functional improvement that is independent from behavior alone. It allows us to determine what neural systems

Summary

This brief review highlights the importance of understanding neural plasticity in neurorehabilitation. Characterizing the neural and behavioral signals that drive plasticity in concert with identifying the neural strategies employed during rehabilitative training can guide the development of novel, more effective, therapeutic strategies.

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