Spasticity After Spinal Cord Injury

After spinal cord injury (SCI), damage to descending motor pathways has been associated with the development of spasticity (Frigon and Rossignol, 2006; Trompetto et al., 2014). Self-reported questionnaires and clinical exams indicate that individuals with incomplete SCI, who showed residual descending connectivity, have a high prevalence of spasticity compared to individuals with complete SCI (Little et al., 1989; Holtz et al., 2017). In agreement, our recent electrophysiological and spinal cord imaging data in humans with a diagnosis of a clinically motor complete SCI showed the presence of descending motor pathway connectivity in individuals with spasticity compared to those without spasticity (Sangari et al., 2019). However, which descending motor pathways influence spasticity following SCI, and to what extent, remains poorly understood. This proposal has two main goals: 1) to examine the contribution of cortico- and reticulo-spinal pathways to spasticity in upper and lower limb muscles, and 2) to develop strategies to promote functional recovery of upper and lower limb spastic muscles in humans with chronic incomplete SCI. The aims below will test two main hypotheses.

In Aim 1, we will use transcranial magnetic stimulation and startle acoustic stimuli to examine the contribution of the cortico- and reticulo-spinal pathway to upper and/or lower limb muscles electromyographic activity. Spinal cord atrophy and morphological characterization of cortico- and reticulo-spinal pathways will be assessed with high-resolution magnetic resonance imaging. Physiological and neuroimaging outcomes will be associated with clinical assessment of spasticity.

In Aim 2, we propose to enhance cortico- and reticulo-spinal contribution to upper and/or lower limb function in spastic muscles by using a novel intervention combining startle acoustic stimuli with motor training.

This research will provide new knowledge about the contribution of descending motor pathways to the control of spasticity in upper and lower limb muscles following incomplete cervical SCI (Aim1) and might lead to the development of a novel rehabilitation intervention to improve upper and lower limb motor function recovery by enhancing residual descending control over spinal networks (Aim 2).