[ARTICLE] The visual amplification of goal-oriented movements counteracts acquired non-use in hemiparetic stroke patients – Full Text HTML

Abstract

Background: Stroke-induced impairments result from both primary and secondary causes, i.e. damage to the brain and the acquired non-use of the impaired limbs. Indeed, stroke patients often under-utilize their paretic limb despite sufficient residual motor function. We hypothesize that acquired non-use can be overcome by reinforcement-based training strategies.

Methods: Hemiparetic stroke patients (n = 20, 11 males, 9 right-sided hemiparesis) were asked to reach targets appearing in either the real world or in a virtual environment. Sessions were divided into 3 phases: baseline, intervention and washout. During the intervention the movement of the virtual representation of the patients’ paretic limb was amplified towards the target.

Results: We found that the probability of using the paretic limb during washout was significantly higher in comparison to baseline. Patients showed generalization of these results by displaying a more substantial workspace in real world task. These gains correlated with changes in effector selection patterns.

Conclusions: The amplification of the movement of the paretic limb in a virtual environment promotes the use of the paretic limb in stroke patients. Our findings indicate that reinforcement-based therapies may be an effective approach for counteracting learned non-use and may modulate motor performance in the real world.

Introduction

Following stroke, a loss of neural tissue induces drastic neurophysiological changes that often result in cognitive and motor impairments, such as hemiparesis. In order to counteract these deficits patients often introduce compensatory movements (e.g. overutilizing their non-paretic limb). Although these compensatory strategies may immediately improve functional motor performance in activities of daily living (ADLs) or reduce the burden of using the paretic limb, a long period of non-use of the affected limb can lead to further reversible loss of neural and behavioral function [1]. This so-called learned non-use has been associated with a reduced quality of life. Hence, methods must be found to reduce the impact of acquired non-use.

A possible treatment for learned non-use is Constraint Induced Movement Therapy (CIMT), which forces the patient to use the paretic limb by constraining the movement of the non-paretic limb. This technique has been shown to be effective in mitigating the effects of learned non-use [2]–[4]. However, due to the high intensity and long duration of CIMT protocols, which can range from 1 to 6 hours of training per session [5], they may reduce quality of life, affect the patient’s adherence to therapy, be prohibitively expensive and even inconvenient for those patients with severe motor or cognitive deficits [6]. Moreover, it remains unclear whether the standard CIMT protocols are more beneficial than bimanual functional rehabilitation [7]. The success rate of the standard CIMT protocols may depend on the severity of upper limb paresis and latency of intervention post-stroke. Consequently, its application remains restricted to subacute patients, with no severe cognitive impairments, and mild hemiparesis. These very stringent inclusion criteria only account for about 15 % of stroke cases [8]. Hence, in light of these limitations it seems opportune to develop rehabilitation techniques that build on the positive aspects of CIMT, i.e. enhanced use of the paretic limb, while mitigating the negative ones.

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