Cortical electrical stimulation combined with motor rehabilitation following unilateral cortical lesions: effects on behavioral performance and brain plasticity

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Adkins, DeAnna Lynn

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Motor impairments are one of the most common deficits resulting from strokes in humans. Motor rehabilitation can often either accelerate and/or enhance functional recovery. Clinical data also indicates that motor cortical electrical stimulation may reduce motor impairments. Thus it seemed likely that combining cortical electric stimulation with rehabilitative training on a motor task could facilitate greater functional recovery. The general hypothesis is that cortical electrical stimulation (CS) can improve the efficacy of motor rehabilitative training and increase neuronal structural plasticity after stroke-like damage in adult animals. This was tested following ischemic SMC lesions in adult male rats using low-levels (below the level of current that elicits movement) of electrical current delivered to the surface of intact tissue adjacent to the lesion concurrent with motor rehabilitative training on a skilled reaching task. In separate studies, it was demonstrated that 50Hz bipolar or 100Hz monopolar cathodal and anodal electrical CS of peri-infarct tissue augmented forelimb functional recovery on skilled reaching tasks compared to rehabilitation alone. However, CS may be partially limited in effectiveness by the severity of post-lesion impairments. CS did not improve overall reaching successes in the single pellet retrieval task in animals with relatively severe impairments following SMC lesions, although CS did alleviate specific movement impairments related to reaching in both moderately and severely impaired groups. It was also hypothesized that cortical stimulation facilitates behavioral improvements by inducing neural structural reorganization after brain damage. It was found that CS-induced improvements in behavior coincided with structural plasticity in the cortex adjacent to the lesion. Rehabilitation combined with 50Hz stimulation increased the surface density of dendritic processes in layer V of the cortex lateral to the lesion compared to groups receiving 250Hz CS or no stimulation during rehabilitation. Cathodal 100Hz CS also enhanced neuronal density, but not neuron number, in perilesion motor cortex compared to groups receiving no stimulation during rehabilitation. Together these studies indicate that cortical electrical stimulation combined with skilled reaching can greatly enhance post-lesion behavioral recovery on skilled reaching tasks. Enhanced behavioral recovery is accompanied by neuroplasticity in cortical areas adjacent to the lesion.