Neural plasticity and neurorehabilitation: Teaching the new brain old tricks
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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2021, Brain Research BulletinCitation Excerpt :This time window represents an important treatment goal to maximize the efficacy of rehabilitation interventions (Bernhardt et al., 2017). Also, the knowledge of the relationship between different neural strategies, mechanisms of neural plasticity and behavioral changes can contribute to improve the rehabilitation process (Kleim, 2011). Thus, it is necessary to develop effective neurorehabilitation interventions to optimize arm function and decrease post-stroke disability.
Longitudinal fMRI measures of cortical reactivation and hand use with and without training after sensory loss in primates
2021, NeuroImageCitation Excerpt :It would be useful to evaluate the reach and retrieval behavioral when vision is blocked. Large bodies of evidence indicate that behavioral experience and activity-dependent plasticity are important drivers in functional recovery after injuries, including cut nerves (e.g., Florence et al., 1998, 2001), stroke (e.g., Nudo et al., 1996a; Xerri et al., 1996; Edwards et al., 2019; see Wahl and Schwab, 2014, Dobkin 2008 for review), dorsal rhizotomy (Darian-Smith and Ciferri 2005), and SCI (see Buonomano and Merzenich 1998; Jones 2000; Tetzlaff et al., 2009; Kleim, 2011; Fouad and Tetzlaff, 2012; Sofroniew 2018 for review). Further, the clinical outcome after stroke can be markedly improved by sensory rehabilitation (Kunkel et al., 1999; Kopp et al., 1999; see Taub et al., 2002; Allred et al., 2014 for review).
Regenerated interneurons integrate into locomotor circuitry following spinal cord injury
2021, Experimental NeurologyCitation Excerpt :By analyzing the Power Spectral Densities (PSDs) of swim waves in the physiologically relevant frequency range between 10 and 30 Hz, we found that both the absolute power and frequency of maximum power were significantly different between uninjured and injured fish at 3 dpi, both rostral and caudal to the injury site (Fig. 1B). Significant PSD differences remained in rostral regions at 9 dpi (Fig. 1B), consistent with studies showing a compensatory effect in neural plasticity following injury (Fouad and Tse, 2008; Kleim, 2011; Martinez et al., 2011). In contrast, PSDs caudal to the injury at 9 dpi were statistically indistinguishable from those in uninjured fish (Fig. 1B), indicating recovery of both swim wave power and the peak frequency of maximum power in this region during the period when newly-generated spinal cord neurons begin to appear at the injury site (Briona and Dorsky, 2014).