Drs.Cheol E. Han, Michael A. Arbib and Nicolas Schweighofer all associated with the University of Southern California in Los Angeles conceived and designed the following experiments: CEH MAA NS. Performed the experiments: CEH. Analyzed the data: CEH NS. Contributed reagents/materials/analysis tools: CEH. Wrote the paper: CEH NS.
Motor training with the upper limb affected by stroke partially reverses the loss of cortical representation after lesion and has been proposed to increase spontaneous arm use. Moreover, repeated attempts to use the affected hand in daily activities create a form of practice that can potentially lead to further improvement in motor performance. We thus hypothesized that if motor retraining after stroke increases spontaneous arm use sufficiently, then the patient will enter a virtuous circle in which spontaneous arm use and motor performance reinforce each other. In contrast, if the dose of therapy is not sufficient to bring spontaneous use above threshold, then performance will not increase and the patient will further develop compensatory strategies with the less affected hand. To refine this hypothesis, we developed a computational model of bilateral hand use in arm reaching to study the interactions between adaptive decision making and motor relearning after motor cortex lesion. The model contains a left and a right motor cortex, each controlling the opposite arm, and a single action choice module. The action choice module learns, via reinforcement learning, the value of using each arm for reaching in specific directions. Each motor cortex uses a neural population code to specify the initial direction along which the contralateral hand moves towards a target. The motor cortex learns to minimize directional errors and to maximize neuronal activity for each movement. The derived learning rule accounts for the reversal of the loss of cortical representation after rehabilitation and the increase of this loss after stroke with insufficient rehabilitation. Further, our model exhibits nonlinear and bistable behavior: if natural recovery, motor training, or both, brings performance above a certain threshold, then training can be stopped, as the repeated spontaneous arm use provides a form of motor learning that further bootstraps performance and spontaneous use. Below this threshold, motor training is “in vain”: there is little spontaneous arm use after training, the model exhibits learned nonuse, and compensatory movements with the less affected hand are reinforced. By exploring the nonlinear dynamics of stroke recovery using a biologically plausible neural model that accounts for reversal of the loss of motor cortex representation following rehabilitation or the lack thereof, respectively, we can explain previously hard to reconcile data on spontaneous arm use in stroke recovery. Further, our threshold prediction could be tested with an adaptive train–wait–train paradigm: if spontaneous arm use has increased in the “wait” period, then the threshold has been reached, and rehabilitation can be stopped. If spontaneous arm use is still low or has decreased, then another bout of rehabilitation is to be provided.
Stroke often leaves patients with predominantly unilateral functional limitations of the arm and hand. Although recovery of function after stroke is often achieved by compensatory use of the less affected limb, improving use of the more affected limb by methods such as the Hand and ArmTutor devices, has been associated with increased quality of life. Here, we developed a biologically plausible model of bilateral reaching movements to investigate the mechanisms and conditions leading to effective rehabilitation. Our motor cortex model accounts for the experimental observation that motor training can reverse the loss of cortical representation due to lesion. Further, our model predicts that if spontaneous arm use is above a certain threshold, then training can be stopped, as the repeated spontaneous use provides a form of motor learning that further improves performance and spontaneous use. Below this threshold, training is “in vain,” and compensatory movements with the less affected hand are reinforced. Our model is a first step in the development of adaptive and cost-effective rehabilitation methods tailored to individuals poststroke.
Stroke is the leading cause of disability in the US, and about 65% of stroke survivors experience long-term upper extremity functional limitations. Although patients may regain some motor functions in the months following stroke due to spontaneous recovery, stroke often leaves patients with predominantly unilateral motor impairments. Indeed, recovery of upper extremity function throughthe use of the ArmTutor, for example, in more than half of patients after stroke with severe paresis is achieved solely by compensatory use of the less-affected limb. Improving use of the more affected arm is important however, because difficulty to use this arm in daily tasks has been associated with reduced quality of life.
There is now definite evidence however that physical therapy interventions targeted at the more affected arm can improve both the amount of spontaneous arm use and arm and hand function after stroke. The Tutor system being one of the best tools currently being used. Further, even after motor retraining is terminated, performance can further improve in patients with less severe strokes in the months following therapy. A possible interpretation of this result is that the repeated attempts to use the affected arm in daily activities are a form of motor practice that can lead to further improvements in motor performance.
The neural correlates of motor training after stroke have been investigated in animals with motor cortex lesions. Specifically, a focal infarct within the hand region of the primary motor cortex causes a loss of hand representations that extends beyond the infarction. However, several weeks of rehabilitative training can overcome this loss of representation, and yield an expansion of the hand area to its prelesion size; the larger area in turn has been correlated with higher level of performance. Long-term potentiation in pyramidal neuron to pyramidal neuron synapses has been demonstrated in horizontal lateral connections, and may provide the basis for map formation and reorganization in the motor cortex, and motor skill learning[.
Contrasting with the increase in performance due to spontaneous recovery, a concurrent decrease of spontaneous arm use has been proposed to occur following stroke. This decrease may be due both to the higher effort and attention required for successful use of the impaired hand and to the development of learned nonuse [12], in that the preference for the less affected arm is learned as a result of unsuccessful repeated attempts in using the affected arm. The constraint-induced therapy (CIT) protocol, which forces the use of the affected limb by restraining the use of the less affected limb with a mitt, has been specifically developed to reverse learned nonuse. Although its “active ingredients” are still not well understood, CIT has been shown to be effective in the recovery of arm and hand functions after stroke in multisite randomized clinical trials. The Arm and HandTutor have shown to be very effective in this regard. Because 50% of the eventual improvement in use (as measured by the questionnaire-based “motor activity log”) is seen at the end of the first day of CIT, it has been suggested that CIT is effective in reversing learned nonuse. To our knowledge, however, there are no longitudinal data tracking the development of learned nonuse just after stroke and during recovery.
In summary, increase in performance after stroke due to spontaneous recovery, rehabilitation, or both does not appear to correlate simply with spontaneous arm use, and a yet-to-be clarified nonlinear mechanism seems to be at play. Here, we focus on rehabilitation in the control of reaching poststroke, a prerequisite for successful manipulation. We developed a biologically plausible model of bilateral control of reaching movements to investigate the mechanisms and conditions leading to such positive or negative changes in spontaneous choice of which arm to use. Our central hypothesis, based on the above observations, is the existence of a threshold in spontaneous arm use: if retraining after brain lesion (or spontaneous recovery) increases spontaneous arm use above this threshold, performance will keep increasing, as each attempt to use the affected arm will act as a form of motor relearning. The patient will then enter a virtuous circle of improved performance and spontaneous use of the affected arm, and therapy can be terminated. In contrast, if spontaneous use of the arm does not reach this threshold after either natural recovery or rehabilitation, or both, performance will not improve after stroke, and compensatory strategies with greater reliance on the less affected arm will either remain or even develop further.
The HandTutor™ system is an active exercise based hand rehabilitation program that uses the accepted methods of impairment oriented training (IOT) with augmented feedback. The HandTutor™ evaluates and treats finger and hand movement dysfunction through exercises that encourage extension/ flexion of the finger(s) and wrist.
The HandTutor™ consists of a safe comfortable glove, with position and speed sensors that precisely record finger and wrist motion, and dedicated rehabilitation software. The ergonomic gloves come in five sizes for both right and left hands. The rehabilitation system employs the known concept of biofeedback to give occupational and physical therapists access to an affordable user friendly hand rehabilitation package. The HandTutor™ can also be used in combination with the 3DTutor™ for arm rehabilitation. The HandTutor™ is CE medical and FDA certified. See www.HandTutor.com for more information.
The ArmTutor™ has been developed to allow for functional rehabilitation of the upper extremity. The system consists of an ergonomic wearable arm brace and dedicated rehabilitation software. The ArmTutor™ allows for a range of biomechanical evaluation including speed, passive and active range of motion and motion analysis of the upper extremity. Quantitative biomechanical data allow for objective evaluation and rehabilitation treatment follow up. The ArmTutor™ rehabilitation concept is based on performing controlled exercise rehabilitation practice at a patient customized level with real time accurate feedback on the patient’s performance. The exercises are designed in the form of challenging games that are suitable for a wide variety of neurological and orthopedic injury and disease. The games challenge the patient to perform the exercise task to their best ability and to continue exercise practice.
The ArmTutor™ allows for isolated and a combination of elbow and three directional shoulder treatment. The system provides detailed exercise performance instructions and precise feedback on the patients exercise performance. Controlled exercise of multijoints within the normal movement pattern prevents the development of undesired and compensatory joint movement and ensures better performance of functional tasks.
The ArmTutor™ together with its sister devices (HandTutor, LegTutor, 3DTutor) is used by many leading rehabilitation centers worldwide and has full FDA and CE certification. See www.HandTutor.com for more information.
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