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Fri, July 9

Speaker: Claire Honeycutt, PhD

Title: Effect of cortical stroke on brainstem structures: Preliminary insights from startle induced release of pre-planned movements following stroke

Abstract: Cortical stroke survivors are afflicted with abnormal patterns of muscle activation which limit their ability to perform basic reaching tasks. The neural mechanisms leading to these abnormal movement patterns remain unclear, though it has been suggested that they may reflect an increased reliance on brainstem pathways.

Hence, an understanding of how brainstem function is altered following stroke is important for assessing how they may contribute to motor impairments.

In this study, we investigated brainstem function following stroke using startling acoustic stimuli. In unimpaired individuals, startling acoustic stimuli can trigger the early release of a pre-planned motor action. This phenomenon is often called startReact.  Animal and human studies indicate that this early release of planned movement bypasses cortical initiation.  Our objective was to quantify the startReact response in stroke patients thereby observing the impact of stroke on brainstem structures related to movement initiation.  We evaluated the patterns of activity in 4 arm muscles during voluntary reaching and startReact (reaching initiated by a loud acoustic stimulus) in 4 stroke subjects performing ballistic elbow extension and flexion movements of 25 degrees.

We found that the startReact reflex appears intact when stroke subjects were performing flexion.  In contrast, during extension the reflex was impacted by the stroke, specifically the muscle activation patterns were distintive. These results demonstrate that the brainstem mediated reflex of startReact is affected following stroke.  However, it is affected differently in extension and flexion tasks.