Spasticity is a common condition after stroke. Clinically, spasticity can be recognized as a velocity-dependent increase in stretch reflexes, and is one of the primary sources of motor impairment in individuals with chronic stroke. While a lot of research has addressed how spasticity modulates the gain of short-latency reflexes, much less is known about the neural pathways that regulate the long-latency responses, a fundamental component of the human motor control system that is severely affected in patients with post-stroke spasticity. In this project, we will develp StretchfMRI, a new measurement technique that combines an MRI-compatible robot with muscle electromyography and with high-resolution functional imaging of the brainstem via fMRI. StretchfMRI will enable, for the first time in vivo and in human, the measurement of activity of brainstem nuclei during long-latency responses. In this project, we will use StretchfMRI to establish the direct involvement of nuclei in the reticular formation in producing a long-latency response. The technique developed in this project is an important step towards a quantitative understanding of basic principles of neuromuscular control, and has important applications in assessing neuromotor impairment and recovery after stroke. StretchfMRI lays the groundwork for establishing causality in cortico-reticular function associated with LLRs. In future work, we plan to apply StretchfMRI in a patient population to study the neural correlates underscoring spasticity in patients with stroke-induced motor impairment.
Stroke is a leading cause of long-term disability in the United States; 30% of stroke survivors are affected by chronic spasticity. In this project, we will develop a new experimental technique, StretchfMRI, and use it to advance the understanding of the neural substrates of long-latency responses, a primary component of motor control affected by spasticity. The future application of this technique to a patient population will lead to a more accurate and neuroscience-grounded assessment of motor impairment and spasticity in stroke.
