Cortical plasticity and rehabilitation

Abstract

The brain is constantly adapting to environmental and endogenous changes (including injury) that occur at every stage of life. The mechanisms that regulate neural plasticity have been refined over millions of years. Motivation and sensory experience directly shape the rewiring that makes learning and neurological recovery possible. Guiding neural reorganization in a manner that facilitates recovery of function is a primary goal of neurological rehabilitation. As the rules that govern neural plasticity become better understood, it will be possible to manipulate the sensory and motor experience of patients to induce specific forms of plasticity. This review summarizes our current knowledge regarding factors that regulate cortical plasticity, illustrates specific forms of reorganization induced by control of each factor, and suggests how to exploit these factors for clinical benefit.Keywords: Cortical plasticity; Experience-dependent plasticity; Cortical reorganization; Neuromodulators; Cholinergic; Rehabilitation Factors that regulate plasticityPlasticity is the remarkable ability of developing, adult, and aging brains to adapt to a changing world. This potential is revealed whenever an organism must meet a new environmental demand or recover from nervous system damage. Plasticity occurs in sensory and motor systems following deprivation of input or overstimulation, increased or decreased usage, learning of new skills, and injury. These experience-dependent changes can be as subtle as a change in neuronal excitability (Engineer et al., 2004) or as dramatic as the rewiring of auditory cortex to process visual information (Sur et al., 1988). Topographic maps, receptive field (RF) size, neuronal firing rate, temporal precision, and combination sensitivity can all be modified by our experiences. The types of plasticity activated by specific situations depend on the nature of the experiences and their behavioral significance, conveyed by release of modulatory neurotransmitters (Fig. 1). Attentional modulationNeural plasticity is essential for adapting to changes in the environment but plasticity can be destabilizing if not well regulated. Limiting plasticity prevents meaningless events from driving changes that could degrade previously acquired memories and skills. Attention plays a key role in the regulation of plasticity associated with sensory experience. Repeated sensory stimulation alters topography in primary sensory cortex only when monkeys use the stimuli to make behavioral judgments (Recanzone et al., 1992(Recanzone et al., , 1993. Many studies have shown that cortical neurons respond differently to attended versus unattended stimuli. Neurons in secondary somatosensory cortex, for example, exhibit greater response synchronization when monkeys are engaged in a tactile task (Steinmetz et al., 2000). Attention can also directly affect firing rates of cortical neurons (Treue and Maunsell, 1999;Recanzone and Wurtz, 2000). Results from several psychophysical studies support the hypothesis that attention re...

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