Abstract
BackgroundProprioception plays important roles in planning and control of limb posture and movement. The impact of proprioceptive deficits on motor function post-stroke has been difficult to elucidate due to limitations in current tests of arm proprioception. Common clinical tests only provide ordinal assessment of proprioceptive integrity (eg. intact, impaired or absent). We introduce a standardized, quantitative method for evaluating proprioception within the arm on a continuous, ratio scale. We demonstrate the approach, which is based on signal detection theory of sensory psychophysics, in two tasks used to characterize motor function after stroke.MethodsHemiparetic stroke survivors and neurologically intact participants attempted to detect displacement- or force-perturbations robotically applied to their arm in a two-interval, two-alternative forced-choice test. A logistic psychometric function parameterized detection of limb perturbations. The shape of this function is determined by two parameters: one corresponds to a signal detection threshold and the other to variability of responses about that threshold. These two parameters define a space in which proprioceptive sensation post-stroke can be compared to that of neurologically-intact people. We used an auditory tone discrimination task to control for potential comprehension, attention and memory deficits.ResultsAll but one stroke survivor demonstrated competence in performing two-alternative discrimination in the auditory training test. For the remaining stroke survivors, those with clinically identified proprioceptive deficits in the hemiparetic arm or hand had higher detection thresholds and exhibited greater response variability than individuals without proprioceptive deficits. We then identified a normative parameter space determined by the threshold and response variability data collected from neurologically intact participants. By plotting displacement detection performance within this normative space, stroke survivors with and without intact proprioception could be discriminated on a continuous scale that was sensitive to small performance variations, e.g. practice effects across days.ConclusionsThe proposed method uses robotic perturbations similar to those used in ongoing studies of motor function post-stroke. The approach is sensitive to small changes in the proprioceptive detection of hand motions. We expect this new robotic assessment will empower future studies to characterize how proprioceptive deficits compromise limb posture and movement control in stroke survivors.
Highlights
Proprioception plays important roles in planning and control of limb posture and movement
Sixteen unilateral, hemiparetic stroke survivors (SS) and sixteen neurologically intact control (NIC) subjects gave written, informed consent to participate in this study, which was approved by Institutional review board (IRB) committees at Marquette and Northwestern Universities
We cannot say with confidence whether the remaining subject (SS04) was able to perform two-alternative discrimination tasks reliably because he responded correctly only 70% of the time when presented with contrasting stimuli that were readily discriminated by every other participant
Summary
Proprioception plays important roles in planning and control of limb posture and movement. The impact of proprioceptive deficits on motor function post-stroke has been difficult to elucidate due to limitations in current tests of arm proprioception. Motor impairments are the most frequent and conspicuous deficits that occur after stroke, and many clinical tests have been developed to obtain standardized measures of limb mobility. Because experimental evidence suggests that these two aspects of control may be differentially affected post-stroke [10], increased understanding of how proprioceptive deficits compromise control of limb posture and movement may prove useful for developing new physical rehabilitation strategies targeting each aspect of control after stroke and for determining which therapeutic approach might best benefit any given patient
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