Objective The startle reflex elicits involuntary release of planned movements (startReact). task-inappropriate flexor activity causing poor elbow extension movement and target acquisition. Results Task-inappropriate flexor activity increased with impairment resulting in larger flexion deflections away from the subjects’ intended target corresponding to decreased target acquisition. Conclusions We conclude that this task-inappropriate flexor activity likely results from cortical or corticospinal damage leading to an unsuppressed or hypermetric classic startle reflex that interrupts startReact elbow extension. Significance Given startReact’s functional URB754 role in compensation during environmental disturbances URB754 our URB754 results may have important implications for our understanding deficits in stroke survivor’s response to unexpected environmental disturbances. Keywords: Startle stroke startReact reaching INTRODUCTION A unique house of the startle reflex URB754 is usually its ability to involuntary elicit pre-planned movements throughout the entire arm (Carlsen et al. 2004 Carlsen et al. 2011 Honeycutt et al. 2013 Rothwell et al. 2002 Valls-Solé et al. 2008 Valls-Solé et al. 1999 When a startling acoustic stimulus is usually offered in the absence of a movement plan the classic startle reflex triggers brief co-contraction of muscle tissue resulting in the individual assuming a protective stance – arm flexion in the upper limb. However when a subject is in a state of movement preparation a startling acoustic stimulus involuntarily elicits the prepared movement (Carlsen et al. 2004 Rothwell et al. 2002 Valls-Solé et al. 1999 Valls-Solé et al. 1995 This phenomenon has been called startReact (Valls-Solé et al. 1999 Different from the classic startle response startReact movements are not significantly different from voluntarily executed movements and reflect the elegance of voluntarily planned movements in terms of acceleration and target accuracy (Carlsen et al. 2004 Carlsen et al. 2004 While the classic startle response results in the generation of a protective crouched posture the startReact response appears to be more functionally relevant; specifically it has been implicated in the ability to actively resist perturbations of the arm and whole-body. We recently exhibited that arm perturbations like startling acoustic stimuli elicit startReact movements (Ravichandran et al. 2013 indicating that the functional role of this reflex likely participates in the effective and efficient response to an environmental perturbations. The startle reflex is also brought on during whole-body perturbations indicating startReact movements may also be functional during balance difficulties (Blouin et al. 2006 Campbell et al. 2012 Oude Nijhuis et al. 2010 Siegmund et al. 2008 The startReact phenomenon was recently shown to improve elbow flexion movements in stroke survivors (Honeycutt and Perreault 2012 but startReact extension movements were impaired. While voluntary movements were slower with impaired muscle mass activity patterns startReact elbow flexion movements were not statistically different from age-matched unimpaired individuals opening a conversation about its potential use in therapy. However confounding results were found during elbow extension. While there was evidence that startReact extension movements were present elbow extension was interrupted by task-inappropriate flexor Rabbit Polyclonal to MYL3. activity causing either delay in elbow extension or elbow flexion away from a subject’s intended target. The specific mechanisms driving this improper flexor activity are unknown making it challenging to properly develop startReact as a therapy tool. However evaluating the impact of impairment level on task-inappropriate flexor activity following cortical stroke could shed some insight. Impairment level is usually linked to both lesion size and damage to the corticospinal tract (Ciccarelli et al. 2008 Mohr et al. 1993 Rogers et al. 1997 Saver et al. 1999 Zhu et al. 2010 By investigating changes in task-inappropriate flexor activity with impairment level we can gain insight into the role of the cortex and the corticospinal tract in its expression. Therefore our objective was to quantify deficits in.