Teaching Interests:
Biomechanics, Rehabilitation Engineering, Motor Control
Research Interests:
My research interests involve the study of neurological rehabilitation with a focus on examining the spinal mechanisms underlying the control of movement and posture in individuals with neuromotor deficits such as stroke and spinal cord injury (SCI). Because the spinal cord contributes to the functional capabilities of the limb during voluntary motor tasks, much can be understood about how it contributes to impaired limb function following upper motor neuron lesions. This knowledge may be especially beneficial in rehabilitation where treatment strategies result in variable outcomes and often focus on sensorimotor retraining without a firm basis of the underlying mechanisms that cause these deficits. Therefore, my research goal is to conduct clinical studies that improve our knowledge of the mechanisms contributing to neuromotor dysfunction and enhance functionally relevant methods for clinical rehabilitation. Several of my ongoing research projects are described below.
Project 1: Quantifying the regulation of whole arm mechanics following stroke. Return of arm function is one of the most common patient goals following neurological injury and the restoration of intralimb coordination and control remains an important goal in physical therapy. Following stroke, the coordination of arm muscle activity often is severely impaired, as exhibited by the emergence of abnormal muscle activation patterns when generating volitional torques about the shoulder and elbow. These patterns, which arise from excess muscle coupling, significantly limit use of the affected limb thus restricting activities of daily living. Rehabilitation paradigms for retraining arm function and reducing abnormal muscle coupling have been limited by a lack of understanding of the mechanical consequences of this discoordination as well as the underlying physiological mechanisms. Most studies have focused on disrupted cortical control, but there is growing evidence that altered spinal function also is likely to contribute to the muscle synergies observed following stroke as well as to impairments such as spasticity and paresis. A quantitative understanding of the spinal contributions to these motor deficits will help target rehabilitation interventions to the underlying mechanisms. To date, the majority of studies quantifying spinal function following stroke have focused on stretch reflexes elicited by passive movements of a single joint. These studies have demonstrated that stretch reflexes are enhanced following stroke and that they significantly alter the regulation of single joint mechanics. It also has been suggested that abnormal reflexes contribute to the clinically observed motor dysfunctions. Although useful, passive studies at individual joints do not address reflex contributions to multijoint coordination during volitional tasks. Hence, the purpose of this study is to quantify how stroke alters the regulation of multijoint mechanics during voluntary muscle activation and to quantify the reflex contributions to this discoordination. This project is in close collaboration with Drs. Eric Perreault and William Zev Rymer at the Rehabilitation Institute of Chicago and Northwestern University.
Project 2: Quantifying the heteronymous contributions to multijoint reflexes. Increasing evidence suggests that stretch reflexes contribute to abnormal coordination following insult to the central nervous system such as stroke or SCI. However, few studies have addressed the role of stretch reflexes in the unimpaired control of multijoint movement and posture. The purpose of this project is to examine the contributions of heteronymous stretch reflex pathways on muscle coordination following whole limb perturbations. Our hypothesis is that heteronymous reflexes are necessary to account for the patterns of muscle activation observed in response to postural disturbances of the human arm. During this investigation, stretch reflexes are elicited via 3-dimensional (3D) postural perturbations to the endpoint of the arm with a robotic interface. We track joint angles using an optical tracking system and estimate muscle length changes with a 3D biomechanical model of the arm; Monte Carlo analyses assess prediction accuracies. Surface EMGs are recorded from 8 muscles that span the shoulder and elbow. Excitatory EMG responses during muscle shortening and inhibitory responses during lengthening are considered as evidence of significant heteronymous reflexes. Our preliminary results show coordinated reflex response following perturbations of whole limb posture [16]. This is not simply due to biomechanical coupling rather it appears that the coordination is due in part to neurally-mediated reflex connections between muscles. This project assesses multijoint reflex responses under functionally relevant conditions to provide insight into their contributions to the coordination of muscles crossing the elbow and shoulder. This project is in close collaboration with Dr. Eric Perreault at Northwestern University.
Project 3: The statistical structure of hand movement following stroke. Movement clearly is impaired following CNS disorders and carries a lot of information and in some sense even defines the disease state of a stroke survivor. Current clinical assessments are not very specific with respect to pinpointing either impairment or disability. Our working hypothesis is that more recently developed signal analysis tools will allow for a more detailed assessment of motor impairment and disability and thus can improve clinical assessments. These assessments are important for patient care and rehabilitation progression. The goals of this project are to determine statistically how indicative natural and naturalistic movements are about the disease state of a population of stroke survivors. This goal will be achieved using a series of experiments and analyses that progress from simple laboratory movements such as pointing to a target (Aim 1) via more complicated tasks such as simple manual construction tasks (Aim 2). State of the art machine learning algorithms will be used to characterize the disease state (Aim 3). Our goal is to demonstrate that tools based on the statistics of movement are at least as good as current clinical assessments (Aim 3). Towards this aim we will try and develop the simplest tests that still allow for an accurate determination of the disease parameters. The tools that we will develop will allow for rapid and consistent assessment of the disease state. Moreover, we will determine exactly which functional limitations are identified by current assessment scales. This project is in direct collaboration with Drs. Konrad Köerding and Eric Perreault at Northwestern University and the Rehabilitation Institute of Chicago.
Project 4: Examining the effects of intermittent hypoxia on neuromotor function following SCI. Earlier studies by Gordon Mitchell and colleagues found that intermittent bouts of low oxygen (hypoxia) has been shown to induce spinal cord plasticity and enhance respiratory function in spinalized rats. Intermittent hypoxia elicits sprouting of neural synapses within the spinal cord and drives long-term facilitation of motor function. Similar potentiation is likely in spinal-injured humans, but previous studies have not addressed this possibility. Therefore, we plan to quantify changes in voluntary motor behaviors during bouts of intermittent hypoxia in persons with SCI. Our hypothesis is that intermittent hypoxia will augment force production via modulation of descending control pathways and enhancement of neuromotor circuitry following SCI. These effects will be quantified using measurements of ankle torque and reflex responses to electrical stimuli or ankle joint movement perturbations. Measurement of torque generation at the ankle will be performed through isometric and isokinetic testing. This project is first to examine the effects of breathing low oxygen levels, delivered intermittently, on muscle performance in the impaired legs of persons with incomplete SCI and may be of great benefit for persons with SCI who present with significant loss of volitional movement. This project is in direct collaboration with Drs. William Zev Rymer (Northwestern and Rehabilitation Institute of Chicago), Brian Schmidt (Marquette U), George Hornby (Rehabilitation Institute of Chicago), and Gordon Mitchell (U of Wisconsin)