Influence of Smooth Pursuit Eye Movements on Long Latency Reflexes During Postural Adjustments in Upright Reaching Movements

open_access
Open Access
Author:
Spasic, Ana
Area of Honors:
Kinesiology
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
Tarkeshwar Singh, Thesis Supervisor
Mark Dyreson, Thesis Honors Advisor
Keywords:
long-latency reflexes
perturbation
posture stabilization
EMG
center of pressure
compensatory postural adjustments
Abstract:
Sensorimotor control and coordination between the upper and lower limbs are essential for daily activities. Even simple tasks, such as reaching for a door handle, require supraspinal pathways to integrate sensory input and accurately scale motor responses. The sensorimotor system adapts to dynamic environments through long-latency reflexes (LLRs), which are bursts of muscle activity (50–100 ms post-perturbation) that help restore movement trajectory. These reflexes incorporate knowledge of limb dynamics and are modulated by the motor cortex, reticular formation, and cerebellum. Mechanical perturbations to the upper limbs can elicit postural responses in the lower limbs, aiding stabilization. This study examines LLR activity in five selected muscles of the upper and lower limbs during upright reaching movements interrupted by unexpected perturbations. Participants aimed to meet a virtual object at a target location by performing a lateral reaching movement while a 10 N force was applied either toward or away from the body at early or late in the movement. Two conditions were tested: pursuit, where participants visually tracked a moving object, and fixation, where they focused on a static target. Since gaze direction influences sensory feedback processing, pursuit was expected to provide richer dynamic feedback. Studying LLRs shows how the body adapts to unexpected movement disturbances, and it enhances our understanding of motor disorders for better diagnostics and rehabilitation strategies. Results showed significant differences in triceps brachii activation following late perturbations, while anterior/posterior deltoid, gastrocnemius, and tibialis anterior activation did not significantly vary across conditions. A potential limitation of the study was the small sample size, suggesting that a larger population may yield more robust findings.