It's been 8.5 years, has your doctor done ONE DAMN THING with this?
Bilateral Synergy: A Framework for Post-Stroke Rehabilitation
Abstract
Background
Unilateral stroke produces debilitating deficits in voluntary control in the contralesional arm, and significant motor coordination deficits in the ipsilesional arm. In addition, patients tend to avoid bilateral arm patterns and during performance of activities of daily living. Nevertheless, upper extremity physical rehabilitation predominantly focuses on motor training activities with only the paretic arm. This can be limiting because of persistent deficits in the ipsilesional arm, and because of the tendency of patients to avoid spontaneous bilateral arm patterns.
Proposition
Rehabilitation should focus on bilateral training to advance recovery of function in both arms of stroke patients, as well as to facilitate spontaneous bilateral arm use. This paper reviews the rationale for this approach, citing evidence for significant hemisphere specific bilateral motor deficits in stroke patients, which affect both the contralesional and the ipsilesional arm. The rationale for, and advantages of, training both arms simultaneously through bilateral tasks is reviewed. Although bilateral training has been employed to treat stroke patients previously, this has tended to focus on bimanual ‘coupling’ as a rationale for performing parallel, but not cooperative bilateral tasks. Bilateral synergy provides a more functional framework for structuring post-stroke upper extremity rehabilitation.
Conclusion
Bilateral synergy may be causally linked to spontaneous bilateral arm use, suggesting that rehabilitation should be focused on bilateral cooperative tasks, such as bilateral object transport. Further research is required to determine whether this approach could be efficacious for patients with hemiparesis, and whether both left and right hemisphere strokes can benefit from such intervention.
Introduction
It has been well-established that unilateral stroke results in sensorimotor deficits in both arms of stroke patients, which is often manifested by hemiparesis and deficits in voluntary control in the contralesional arm [1–6], and also by significant coordination deficits in the ipsilesional arm [7–21]. Nevertheless, the primary goals of upper extremity physical rehabilitation continue to focus on recovery of function in the paretic arm alone [22–28]. This can be limiting, even when contralesional arm control improves, because persistent deficits in the ipsilesional arm can limit both recovery of function and carry-over of training into natural settings [29–31]. Physical rehabilitation should focus on bilateral training to advance recovery of function following stroke. This approach has the advantages of promoting recovery in both arms, and of specific training of bilateral movements, which can directly improve performance on activities of daily living (ADL). Physical rehabilitation could be enhanced by exploiting the cooperative action of both hands during common goal directed activities. Such training should enhance spontaneous use of bilateral patterns, which may be critical in promoting spontaneous use of both arms during ADL and thus requisite to more improvements in functional recovery. This paper presents a rationale for training both the contralesional and ipsilesional arms in physical rehabilitation, for focusing on bilateral tasks, and finally for exploiting cooperative, as opposed to parallel, bilateral tasks to elicit bilateral synergies.
Strong rationale for focusing upper limb rehabilitation on bilateral movements have previously been delineated [29,32– 34]. Nevertheless, upper limb physical rehabilitation continues to focus predominantly on movement experiences with the contralesional arm. The rationale for this focus is likely that recovery of bilateral patterns will naturally emerge, when paresis is diminished. Indeed, it is well understood that functional activities of daily living are overwhelmingly dependent on bilateral movements [10]. However, this view fails to recognize that substantial movement deficits also occur in the non-paretic arm. In addition, specific deficits in bilateral coordination have been shown to result from unilateral sensorimotor stroke [30,35–37]. In fact, even patients with mild paresis tend to avoid spontaneous use of the contralesional arm to assist with ADL that are normally performed using bilateral arm patterns [10,38]. Thus, specific training in bilateral movements seems to be critical to reestablish spontaneous bilateral arm use during ADL. The following sections will present evidence for bilateral motor deficits in stroke patients, the importance of focusing rehabilitation on both arms, and on bilateral movements.
The hemisphere-specificity of the sensorimotor deficits that result from unilateral stroke appears to result from the lateralized organization of motor functions in the cerebral cortices. Previous research from our laboratory has indicated that two aspects of motor control have become specialized to different hemispheres: The right hemisphere for control of limb impedance, and the left hemisphere for predicting task dynamics [39]. Whereas, the specific processes that have become lateralized remain controversial [18,40–44], the effect of lateralization in motor control processes is that unilateral movements require both hemispheres to contribute their specializations to motor performance. Thus, when one hemisphere is lesioned, hemisphere-specific motor deficits become evident in both arms of stroke patients. This bi-hemispheric control scheme is consistent with neuroimaging studies that have revealed activation in motor cortical areas of both brain hemispheres during unilateral hand and arm movements [45–51].
Consistent with the idea that both contralateral and ipsilateral hemisphere mechanisms are critical for control of unilateral movements, hemisphere-specific ipsilesional deficits reflect the specializations of each hemisphere for different movement control processes [16,17,52–56]. Not suprisingly, these deficits in motor coordination and learning reflect the functional advantages that were previously reported for the dominant and non-dominant arms of healthy subjects that are associated with handedenss [39,57–63]. More specifically, left hemisphere damage is associated with ipsilesional deficits in intersegmental coordination and trajectory smoothness, while right hemisphere damage is associated with deficits in final position accuracy [39]. Other studies have shown that left hemisphere damage produces deficits in the early phase of motion, while right hemisphere damage produces deficits in the later phase, supporting a dissociation between predictive and feedback mediated control processes [17,64]. Desrosiers et al. [21] and Schaefer et al. [53] emphasized the functional importance of these deficits by reporting correlations with deficits in clinical movement evaluations that include simulated activities of daily living. Taken together this research supports a bi-hemispheric model of control, in which each hemisphere contributes specialized processes to each arm. A strong prediction of this model is that hemisphere specific deficits should occur in the contralesional as well as the ipsilesional arms of stroke patients. In support of this prediction, Robertson et al. [65] revealed coordination deficits in both arms of stroke patients with left hemisphere damage that were consistent with previous reports of intersegmental coordination deficits [53]. We recently expanded this support by demonstrating that left hemisphere lesions produce contralesional deficits in directional control and trajectory straightness, whereas, right lesions produce contralesional deficits in movement termination [6]. In summary, there has been substantial support for the idea that the lateralized organization of motor control systems in the brain leads to hemisphere-specific deficits in both arms of stroke patients. These findings support a lateralized, bi-hemispheric model of motor control and emphasize the importance of focusing rehabilitation on both arms of unilaterally lesioned stroke patients.
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