Brian D. Schmit - US grants

The purpose of this research partnership is to investigate the functional implications of using sensor feedback to enhance motor control of the arm post-stroke. Two key functional aspects of motor control of the arm will be examined: 1) Reach, which involves coordinated actions of the shoulder and elbow musculature and 2) grasp, which incorporates both finger position and force controls. For each system, we will demonstrate that sensory feedback from nonhomologous joints has a significant effect on motor control. Initially, we will examine the intralimb reflex coupling of wrist/hand sensory feedback on elbow and shoulder musculature and visa versa. For Aim 1 of this study, we will show that motorized stretch of the elbow and fingers produces reflex activity in muscles that are not perturbed. These effects will be compared between post-stroke and neurologically intact individuals using tendon tap perturbations. Sensory manipulations consisting of posture electrical stimulation, vibration and anesthesia will be used to modify the heteronymous reflex responses. Having demonstrated reflex coupling across joints, we will then examine the effects that this reflex coupling may have on motor function. In Aim 2, motor control tasks of the upper arm (e.g. reach) will be tested during sensory manipulations of the fingers and wrist. Similarly, motor tasks of the hand will be tested with modifications of sensory inputs to the elbow and shoulder. These studies will demonstrate that sensory signals from nonhomologous joints can substantialy enhance motor function. The results of this study will suggest a new type of approach for rehabilitation of arm function post-stroke. We postulate that substantial improvements in arm function can be achieved by developing new technologies that provide artificial sensory feedback. In addition, conventional therapies may be applied more efficiently or effectively using the principles that will be demonstrated by this study.

The objective of this study is to identify how the suppression of reflex function by antispastic agents affects volitional movement in people with incomplete spinal cord injury (SCI). Spastic reflexes are commonly treated using medications or other therapeutic approaches without a good understanding of how the subsequent changes in reflex function affect volitional movements, including gait. This study aims to improve our understanding of how reflexes affect functional movements and the impact that oral medications have on reflex regulation of movement in people with incomplete SCI. We will test the effect of two commonly prescribed antispastic oral medications, baclofen and tizanidine, on the reflex regulation of volitional muscle activity and gait. We expect that reflex excitation contributes to the generation of muscle activity during volitional tasks, and antispastic agents will depress reflexes and reduce muscle activity of the legs during gait. A comparison of the effects of reflexes on volitional movements, including gait, and sensitivity to antispastic agents will be made to gain an improved understanding of how different types of incomplete SCI patients utilize reflex activation of muscles to facilitate movement. We anticipate that subjects with greater weakness might rely heavily on reflexes for the generation of muscle activity during movement, and could be detrimentally affected by antispastic medications. This study has important implications for therapies aimed at restoring movement in SCI and for the treatment of spasticity to improve functional movements.

DESCRIPTION (provided by applicant): The regulation of cardiovascular systems during muscle activity is poorly understood in people with incomplete spinal cord injury (SCI). In the past, disruptions in somatomotor and sympathetic control have been investigated separately in SCI. We propose to investigate the coupling of sympathetic and somatomotor control because it is relevant to exercise training paradigms that are designed to improve somatomotor function or enhance physical fitness. Our approach will be to measure tendon tap reflexes, voluntary muscle activation, and blood flow of the knee (below injury) and elbow (above injury) before and after sympathetic stimuli consisting of cold pressor tests, mental math and an acute bout of exercise. These data will provide information about sympathetic control of blood flow during muscle activity. Plasticity of the sympathetic- somatomotor coupling will also be investigated by making measurements before and after a treadmill training exercise program. These experiments will enable us to address three aims. Aim 1 will be to characterize coupling of sympathetic and somatomotor systems below the level of spinal injury. This aim will examine spinal sympathetic and motor reflexes and their interactions. It will also examine how descending somatomotor coupling is disrupted by the spinal injury. In Aim 2, we will identify changes in the interactions of sympathetic and somatomotor systems above a spinal injury. Because of the injury and the changes that occur below the injury, the sympathetic-somatomotor coupling is also likely to be disrupted in the arm. Aim 3 will then demonstrate plasticity of sympathetic-somatomotor coupling after exercise training. Three different eight week exercise training programs will be tested including 1) upper body ergometry, 2) treadmill training with exertion level matched to the upper body ergometry and 3) treadmill training with heart rate matched to an initial test of upper body ergometry. The exercise training will be tested in a randomized crossover study design with three months between exercise training paradigms. We anticipate that there will be plasticity of sympathetic-somatomotor coupling and that the exercise training effects will normalize control of these systems. However, because of the injury, we anticipate that adaptations will differ from non-injured controls. This study has implications for exercise training in human SCI. The coupling of sympathetic and somatomotor systems is expected to depend on whether exercise targets the upper or lower body. The recovery of function requires both the improvement in the control of movement as well as in the regulation of blood flow to active muscle groups. In addition, this study is important for understanding the potential impact of treadmill exercise training on cardiovascular fitness, a topic of increasing interest in people with limitations to physical activity.