An investigation into the StartReact effect in chronic stroke survivors

Abstract

Stroke is one of the leading causes of movement disability in adults globally. The amount of motor disability after a stroke has been correlated to the amount of corticospinal tract damage, which is the major motor pathway damaged following stroke. A notion to improve motor function in stroke survivors is to employ alternate motor fibers, such as the reticulospinal tract (RetST), which may be spared after stroke. RetST originates from the brainstem and terminates at different levels of the spinal cord in the vicinity of motoneurons which opens the possibility of its use in rehabilitation. Prior to any attempt to use RetST in stroke rehabilitation, however, it is important to establish whether RetST could be triggered in stroke survivors non-invasively, and then assess its potential benefits in improving function. One way of targeting the RetST is to use a "StartReact" protocol to foster early release of a pre-planned movement in response to a startling stimulus, suggested to be conveyed via this pathway. The ultimate aim in the current series of doctoral studies was to evaluate the feasibility of using “StartReact” experimental context for stroke rehabilitation. To this end, three studies were completed. The first study was a systematic review with meta-analysis on the ability of a startling stimulus to shorten premotor time (PMT) (“StartReact” phenomenon) in stroke survivors. This study, published in Journal of Neurophysiology (DeLuca et al., 2022), established preservation of “StartReact” phenomenon in stroke survivors using published literature. The second study aimed to identify optimal experimental parameters for facilitating “StartReact” phenomenon in stroke survivors. In a “StartReact” experimental context involving a button press, it was determined in stroke survivors if there was an effect (pre-pulse inhibition or pre-pulse facilitation) on PMT by the ‘warning’ cue being delivered at specific predetermined time (interstimulus interval, ISI) before the ‘go’ cue. Results showed that employed ISI in the range of (50 – 2400 ms) did not have any inhibitory or facilitatory effect on the presentation of “StartReact” phenomenon, and hence could be used in the third and final study. The third study sought to understand kinematic changes during execution of unconstrained discrete goal-directed motor tasks in a “StartReact” experimental context in stroke survivors. Results showed an increase in endpoint accuracy and a kinematic change in joint coordination between the elbow and wrist. The results, show that “StartReact” is a potential method for rehabilitation in stroke survivors and it has further potential to improve functional impairment by promoting changes in movement patterns. Future studies should look to explore the kinematic changes in a larger stroke population.