AUTHOR=Xia Nan , He Chang , Li Yang-An , Gu Minghui , Chen Zejian , Wei Xiupan , Xu Jiang , Huang Xiaolin 

TITLE=Startle Increases the Incidence of Anticipatory Muscle Activations but Does Not Change the Task-Specific Muscle Onset for Patients After Subacute Stroke

JOURNAL=Frontiers in Neurology

VOLUME=Volume 12 - 2021

YEAR=2022

URL=https://www.frontiersin.org/journals/neurology/articles/10.3389/fneur.2021.789176

DOI=10.3389/fneur.2021.789176

ISSN=1664-2295

ABSTRACT=Objectives: To demonstrate the task-specificities of Anticipatory Muscle Activations (AMAs) among different forward-reaching tasks and explore the StartleReact Effect (SE) on AMAs in occurrence proportions, AMAs onset latency or amplitude within these tasks in both healthy and stroke population.
Methods: Ten healthy and ten stroke subjects were recruited. Participants were asked to complete the three forward-reaching tasks (reaching, grasp a ball or cup) on the left and right hand respectively with two different starting signals (warning-Go and warning-startle). The surface electromyography of Anterior deltoid, Flexor Carpi Radialis  and Extensor Carpi Radialis (ECR) on the moving side was recorded together with signals from bilateral trunk muscles. Proportions of valid trials, incidence of SE, AMAs incidence of each muscle and their onset latency/amplitude were involved in analyses. Difference of these variables across different move sides (healthy, nonparetic and paretic), stimuli conditions and the three tasks were explored.
Results: Comparisons between move sides revealed a widespread AMAs dysfunction in subacute stroke survivors which was manifested as lower AMAs onset incidence, changed onset latency and smaller amplitude of AMAs in bilateral muscles. However, a significant effect of different tasks was only observed in AMAs onset latency of muscle ECR , but the significance disappeared in the subsequent analysis of the stroke subjects only. Moreover, the following post hoc comparison indicated significant early AMAs onsets of ECR in task Cup when comparing with Reach. For different stimuli conditions, a significance was only revealed on shortened premotor reaction time under startle for all participants. Furthermore, stroke survivors had a significantly lower incidence of SE than healthy subjects under startle. But all performed higher incidence of ECR AMAs onset than with normal signal. In addition, the incidence of ECR AMAs of both nonparetic and paretic sides could be increased significantly via startle.
Conclusions: Healthy people have task-specific AMAs of muscle ECR when they perform forward-reaching tasks with different hand manipulations. However, this task-specific adjustment is lost in subacute stroke survivors. SE can improve the incidence of AMAs for all subjects in the forward-reaching tasks involving precision manipulations, but not change AMAs onset latency and amplitude.