Does exposure to startle impact voluntary reaching movements in individuals with severe-to-moderate stroke?

Abstract

When movements of individuals with stroke (iwS) are elicited by startling acoustic stimulus (SAS), reaching movements are faster, further, and directed away from the body. However, these startle-evoked movements also elicit task-inappropriate flexor activity, raising concerns that chronic exposure to startle might also induce heightened flexor activity during voluntarily elicited movement. The objective of this study is to evaluate the impact of startle exposure on voluntary movements during point-to-point reaching in individuals with moderate and severe stroke. We hypothesize that startle exposure will increase task-inappropriate activity in flexor muscles, which will be associated with worse voluntarily initiated reaching performance (e.g. decreased distance, displacement, and final accuracy). Eleven individuals with moderate-to-severe stroke (UEFM = 8–41/66 and MAS = 0–4/4) performed voluntary point-to-point reaching with 1/3 of trials elicited by an SAS. We used electromyography to measure activity in brachioradialis (BR), biceps (BIC), triceps lateral head (TRI), pectoralis (PEC), anterior deltoid (AD), and posterior deltoid (PD). Conversely to our hypothesis, exposure to startle did not increase abnormal flexion but rather antagonist activity in the elbow flexors and shoulder horizontal adductors decreased, suggesting that abnormal flexor/extensor co-contraction was reduced. This reduction of flexion led to increased reaching distance (18.2% farther), movement onset (8.6% faster), and final accuracy (16.1% more accurate) by the end of the session. This study offers the first evidence that exposure to startle in iwS does not negatively impact voluntary movement; moreover, exposure may improve volitionally activated reaching movements by decreasing abnormal flexion activity.

Highlights from the 30th Annual Meeting of the Society for the Neural Control of Movement

“…Startle exposure resulted in faster and louder speech. These results were analogous to the finding that a startle during upper extremity movement produced a higher probability of muscle activity onset in severe poststroke subjects who were unable to activate their arm muscles on their own (38). Second, Ding-lan Tang examined movement variability during speech production perturbed by auditory feedback.…”

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

“…At last, our research focused on the initiation of AMAs and did not include classic APA evaluation indicators, such as onset or velocity of displacement of body center of mass on the trunk ( 3 , 5 ) in this study. SE may affect the movement amplitude and velocity of the trunk and limbs of stroke survivors ( 30 , 31 ). The integration of a wearable inertial measurement unit with sEMG may better optimize our conclusions.…”

“…In healthy subjects, the loud acoustic stimulus has been confirmed to increase the response frequency of AMAs during gait initiation ( 4 ). Moreover, some studies further revealed that the exposure to startling does not impact the upper-limb voluntary activities but enhances the actual reaching performance in stroke subjects ( 30 , 31 ). However, not all movement initiation can be triggered by SE early, it is negative in some distal finger manipulation activities ( 32 ).…”

Possibility of that extensors respond faster than flexors for the metacarpophalangeal joints in individuals with severe-to-moderate stroke-caused impairment

“…A total of 7 hemiplegic male volunteers post stroke (age: 61.57±12.03 (S.D) years; impaired side (L/R): 4/3, time since stroke: 7.63±6.51 (S.D) month) participated in the study. The inclusion criteria were moderate-to-severe upper extremity impairment (upper extremity Fugl-Meyer (UEFM) score <41/66 [28]) and sufficient cognitive/language abilities to follow instructions during the experiment (Mini-Mental Status Score >22). We excluded volunteers who had severe shoulder pain, relevant musculoskeletal injury, or fixed contraction deformity in the upper extremity.…”