NSF Award
0302313
0302313<br/>Mirbagheri<br/>Although the precise mechanisms are uncertain, motor impairments in stroke are broadly due to disturbances in descending commands to the spinal cord. Three major mechanisms have been suggested: spasticity, abnormal muscle co-activation, and weakness caused by decreased drive command to motoneurons. These mechanisms also affect joint dynamic stiffness, the dynamic relation between joint position and the torque, which characterizes the interaction between a joint and the mechanical environment. Accordingly, the long-term objective of this research program is to develop advanced engineering techniques to investigate the neurophysiological mechanisms underlying motor impairments in stroke, particularly, through the study of the reflex components of joint dynamic stiffness. Results will provide critical information for understanding the origins of neurological disabilities, thus optimizing the efficacy of therapeutic intervention. The specific aims of the proposed work are 1) to characterize effect of stroke on modulation of joint dynamic stiffness with joint angle and voluntary contraction, 2) to characterize impairment in voluntary movement of the spastic joint, 3) to assess the relationships between the stroke effects on joint dynamic stiffness and impaired voluntary movement, 4) to explore the time course of the relationships in Aim-3 from injury to 12 months, and 5) to characterize effects of stroke on stretch reflex modulation during imposed joint movement.<br/><br/>The mechanical parameters of stretch reflexes have been difficult to study in a clinical setting due to the longstanding lack of accurate and sensitive tools for separating torque generated by reflex mechanisms from torque generated by passive and intrinsic mechanisms. The investigators have developed a novel system identification technique (the parallel-cascade technique) that enables them to characterize joint dynamic stiffness and to separate the relative contributions of its components. The technique will be used to characterize the interactions between abnormal joint dynamic stiffness and impaired voluntary movement during recovery from stroke. Passive, intrinsic and reflex stiffness are expected to be modulated abnormally across test conditions and these abnormalities will be correlated with the parameters of impaired voluntary movement.
