Stretch reflex contributions to human arm impedance following stroke
This study examines the control of human arm mechanics following stroke, and how stretch-sensitive reflexes contribute to this control. Spinal networks integrating peripheral sensory information play an important role in normal motor function and are strongly influenced by descending pathways to the spinal cord. The disruption of these pathways may contribute significantly to the abnormal motor behavior following stroke. Understanding how the spinal regulation of whole limb mechanics is altered and which mechanisms contribute to these alterations may provide key insights for designing effective rehabilitation strategies following cerebral vascular injury. Our current work involves developing methods to quantify stretch reflex contributions to multijoint mechanics and using these methods to examine changes in upper limb function following stroke.
Task-dependent modulation of upper limb reflexes
Single joint studies have demonstrated that a key feature of the stretch reflex is that it can be modulated in a task-dependent manner. Factors that can influence reflex behavior include environmental stability and the instructions to the individual. While it has been suggested that reflex modulation may play a critical role in normal motor function, the mechanisms underlying this modulation are unclear and the degree to which it influences whole limb mechanics is largely unknown. Our current research in this area focuses on elucidating the mechanisms underlying stretch reflex modulation at proximal and distal joints in the upper limb and how this modulation influences whole limb mechanics.
Collaborator: Colum Mackinnon
The role of muscle properties in the regulation of whole limb stiffness and stability
The purpose of this study is to investigate the contribution of muscle properties to limb stiffness and stability in 3D space. Experiments are performed in the feline hindlimb to allow precise measurements of individual muscle properties without reflex or voluntary intervention. The project aims trace the sources of limb stiffness from single muscles, to muscle combinations, to whole limb interactions. These studies will reveal how the unique design of each muscle acts to stabilize the limbs against the perturbations that occur during real 3D movements. This work will also identify how disease-induced changes in muscle architecture and muscle mechanical properties degrade limb stability during movement.
Collaborators: Thomas Sandercock and CJ Heckman
Contributions of primary motor cortex to arm muscle activity
The goal of this study is to develop robust techniques for estimating cortical contributions to upper limb muscle activity. Recent advances in electrode technology make it possible to obtain simultaneous recordings from multiple cortical neurons. Quantifying the relationship between cortical and muscle activities has the potential to greatly increase our understanding of the primate motor system and also may provide a foundation for developing high-speed brain computer interfaces for the severely disabled. However, these and other potential applications for multi-channel electrodes require techniques for handling the vast amounts of data that can be acquired and for determining the relationship between these data and the signal or functional task of interest. We are developing techniques to accomplish this task and using these techniques to assess cortical function in freely moving primates.
Collaborators: Lee Miller, Sara Solla and David Westwick
Following a unilateral stroke, individuals are often left with movement deficits contralateral to the injury site. Restoration of motor function can arise through a number of mechanisms including recovery of the affected tissue or compensation by other brain areas in the same or opposite hemisphere. Different measures of brain function have provided conflicting evidence on the benefits of increased intact hemisphere involvement for restoration of movement control in the affected limb. This study seeks to resolve this issue using transcranial magnetic stimulation and functional MRI to quantify brain function in each hemisphere following stroke and by correlating this function with movement ability.
Contact: Gwyn Lewis
During bimanual mirror or anti-mirror movements, the two hands are constrained to perform as a single functional unit, such that there is a convergence of movement parameters even if unimanual performance differs. When healthy individuals perform bimanual tasks, the dominant limb generally reduces its performance level to match that of the non-dominant. In populations with a unilateral motor deficit, there is evidence to indicate that bimanual training can improve unimanual performance of the affected limb. The neural mechanisms associated with this phenomenon are uncertain. This project examines the behavioral adaptations in the affected limb of post-stroke hemiparetics during performance of a symmetric bimanual task and uses functional imaging techniques to examine the neural pathways activated during this task.
Contact: Gwyn Lewis