Claire Fletcher Honeycutt1, Eric Jon Perreault2. 1. Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, IL, USA. Electronic address: claire.honeycutt@gmail.com. 2. Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, IL, USA; Department of Biomedical Engineering, Northwestern University, Evanston, IL, USA; Department of Physical Medicine and Rehabilitation, Northwestern University, Chicago, IL, USA.
Abstract
OBJECTIVE: The startle reflex elicits involuntary release of planned movements (startReact). Following stroke, startReact flexion movements are intact but startReact extension movements are impaired by task-inappropriate flexor activity impeding arm extension. Our objective was to quantify deficits in startReact elbow extension movements, particularly how these deficits are influenced by impairment. METHODS: Data were collected in 8 stroke survivors performing elbow extension following two non-startling acoustic stimuli representing "get ready" and "go", respectively. Randomly, the "go" was replaced with a startling acoustic stimulus. We hypothesized that task-inappropriate flexor activity originates from unsuppressed classic startle reflex. We expected that increasing damage to the cortex (increasing impairment) would relate to increasing 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 the 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 role in compensation during environmental disturbances, our results may have important implications for our understanding deficits in stroke survivor's response to unexpected environmental disturbances.
OBJECTIVE: The startle reflex elicits involuntary release of planned movements (startReact). Following stroke, startReact flexion movements are intact but startReact extension movements are impaired by task-inappropriate flexor activity impeding arm extension. Our objective was to quantify deficits in startReact elbow extension movements, particularly how these deficits are influenced by impairment. METHODS: Data were collected in 8 stroke survivors performing elbow extension following two non-startling acoustic stimuli representing "get ready" and "go", respectively. Randomly, the "go" was replaced with a startling acoustic stimulus. We hypothesized that task-inappropriate flexor activity originates from unsuppressed classic startle reflex. We expected that increasing damage to the cortex (increasing impairment) would relate to increasing 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 the 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 role in compensation during environmental disturbances, our results may have important implications for our understanding deficits in stroke survivor's response to unexpected environmental disturbances.
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