Understanding Age Effects and Adaptation of Sensory and Motor Rehabilitation Procedures for Stroke Patients

Abstract

Stroke is known to degrade sensory and/or motor processes. This research aimed to assess the functioning of the sensory and motor components of each upper limb/hemisphere system of mild to moderate stroke patients to determine the primary source of impairment. The hypothesis was that individualized specific training (sensory vs. motor) favor the recovery of functional abilities. Sensory and motor alterations, induced by unilateral mild to moderate stroke and aging, were investigated separately. For the sensory system, a 20 degrees elbow flexion reference position was matched with the same or opposite arm, and vibration-induced movement illusion was matched with the opposite arm. For the motor system, an isometric 20% MVC reference elbow extension effort was matched with the same or opposite arm, and an isometric force tracking task was performed with each arm. The same protocols and procedures were used in all studies. The first study investigated the left and right proprioceptive sensory and motor systems in younger and older younger adults. Age was found to induce a decrease in the gain of both systems, transforming asymmetries of position sense, movement sense and sense of effort, as well as force control. The second study investigated the left and right proprioceptive sensory systems in stroke patients. The asymmetry in elbow joint position sense was exacerbated, and attenuation of proprioceptive sensitivity was found when compared to older adults. The third study investigated the alteration of the right and left motor systems in stroke patients. The gain transformation produced by stroke corresponded to an exacerbation of age effects, especially for the affected arm. The last study investigated whether impairment-specific training (proprioceptive vs. motor) improves sensory and/or motor deficits in stroke patients after the identification of their primary deficit. Stroke patients were divided into two groups based on studies 1 and 2 assessments: primary sensory or motor deficit was assigned to corresponding impairment-specific training. A reaching functional task to a small target and training to reproduced with the same arm a reference position or extension effort were performed with the affected arm. The respective deficits observed in studies 1 and 2 were reassessed using the same protocols, respectively. Adaptation of training to the primary deficit leads to functional and sensory or motor improvement for the affected side for 60% of the patients. Although 40% of the patients also showed improvement in some tasks, sensory and/or motor training only was not sufficient, as indicated by limited improvement in the functional task. These results lead us to suggest that (1) age and stroke contributes to alterations in position sense, movement sense, sense of effort and force control that may result from the combination of the structural and neurophysiological reorganization of cortical and, likely, other brain structures, which lead to changes in behaviors, (2) alterations can be viewed as conferring a different gain to the sensory and/or motor systems that transform intrinsic natural asymmetries, which should be considered in rehabilitation, (3) the differentiation of stroke-induced sensory and motor deficits is possible, and (4) recovery by impairment-specific training is positive for the corresponding system in patients but has limited effects when both sensory and motor systems are affected, which appears to be related to stroke severity. The results also indicated that the affected side and handedness are factors to consider in the individualization/adaptation of rehabilitation procedures.