Startling acoustic stimuli elicit rapid hand extension following stroke

Loud startling acoustic stimuli can involuntarily elicit planned movements faster than is possible voluntarily. This phenomenon, known as startReact, is thought to be mediated through brainstem pathways. The startReact can be elicited in stroke survivors with a cortical lesion. This has been demonstrated for elbow motions, thought to have significant input from brainstem pathways. This study sought to determine if the startReact can also be elicited for hand movements following stroke, even though these are driven predominantly by the motor cortex. Data were collected from 8 stroke survivors performing rapid hand extension movements. StartReact responses could be elicited in 7 of 8 subjects. Across all subjects, the startling acoustic stimuli were able to decrease movement times substantially (Δ 57ms; p ≈ 0) when indicators of startle were detected. However, these responses were elicited less frequently than previous reports for startReact at the elbow. Nevertheless, the intact startReact response suggests that the integrity and actions of the pathways mediating this response should be considered when rehabilitating the hand following stroke.