Biology subjects

Sinha, O.

Publications and source records attributed to Sinha, O..

3 recordsLinked to original sources

bioRxiv2024

Predictive posture stabilization before contact with moving objects: equivalence of smooth pursuit tracking and peripheral vision

Postural stabilization is essential to effectively interact with our environment. Humans preemptively adjust their posture to counteract impending disturbances, such as those encountered during interactions with moving objects, a phenomenon known as anticipatory postural adjustments (APAs). APAs are thought to be influenced by predictive models that incorporate object motion via retinal motion and extra-retinal signals. Building on our previous work that examined APAs in relation to the perceived momentum of moving objects, here we explored the impact of object motion within different visual field sectors on the human capacity to anticipate motion and prepare APAs for contact between virtual moving objects and the limb. Participants interacted with objects moving towards them under different gaze conditions. In one condition, participants fixated on either a central point (central fixation) or left-right of the moving object (peripheral fixation), while in another, they followed the moving object with smooth pursuit eye movements (SPEM). We found that APAs had the smallest magnitude in the central fixation condition and that no notable differences in APAs were apparent between the SPEM and peripheral fixation conditions. This suggests that the visual system can accurately perceive motion of objects in peripheral vision for posture stabilization. Using Bayesian Model Averaging, we also evaluated the contribution of different gaze variables, such as eye velocity and gain (ratio of eye and object velocity) and showed that both eye velocity and gain signals were significant predictors of APAs. Taken together, our study underscores the roles of oculomotor signals in modulation of APAs. New and NoteworthyWe show that the human visuomotor system can detect motion in peripheral vision and make anticipatory adjustments to posture before contact with moving objects, just as effectively as when the eye movement system tracks those objects through smooth pursuit eye movements. These findings pave the way for research into how age-induced changes in spatial vision, eye movements, and motion perception could affect the control of limb movements and postural stability during motion-mediated interactions with objects.

neuroscience↗

bioRxiv2024

Short-term performance impairment in adaptive reaching following exercise induced neuromuscular fatigue in lower-limb postural muscles

Neuromuscular fatigue (NMF) induces temporary reductions in muscle force production capacity, affecting various aspects of motor function. While studies have extensively explored NMFs impact on muscle activation patterns and postural stability, its influence on motor adaptation processes remains less understood. This paper investigates the effects of localized NMF on motor adaptation during upright stance, focusing on reaching tasks. Utilizing a force field perturbation paradigm, participants performed reaching movements while standing upright before and after inducing NMF in the ankle dorsiflexor muscles. Results revealed that despite maintained postural stability, participants in the NMF group exhibited larger movement errors during reaching tasks, suggesting impaired motor adaptation. This was evident in both initial and terminal phases of adaptation, indicating a disruption in learning processes rather than a decreased adaptation rate. Analysis of electromyography activation patterns highlighted distinct strategies between groups, with the NMF group showing altered activation of both fatigued and non-fatigued muscles. Additionally, differences in co-activation patterns suggested compensatory mechanisms to prioritize postural stability despite NMF-induced disruptions. These findings underscore the complex interplay between NMF, motor adaptation, and postural control, suggesting a potential role for central nervous system mechanisms in mediating adaptation processes. Understanding these mechanisms has implications for sports performance, rehabilitation, and motor skill acquisition, where NMF may impact the learning and retention of motor tasks. Further research is warranted to elucidate the transient or long-term effects of NMF on motor adaptation and its implications for motor rehabilitation interventions. New & NoteworthyWe assessed motor adaptation during force field reaching following exercise-induced neuromuscular fatigue (NMF) on postural muscles. NMF impaired adaptation in performance. Similarly, diverging activation strategies were observed in the muscles. No effects were seen on measures of postural control. These results suggest the remodulation of motor commands to the muscles in presence of NMF, which may be relevant in settings where participants could be exposed to NMF while learning, such as sports and rehabilitation.

physiology↗

bioRxiv2023

Smooth pursuit eye movements contribute to anticipatory force control during mechanical stopping of moving objects

When stopping a closing door or catching an object, humans process the motion of inertial objects and apply reactive limb force over short period to interact with them. One way in which the visual system processes motion is through extraretinal signals associated with smooth pursuit eye movements (SPEM). We conducted three experiments to investigate how SPEM contribute to anticipatory and reactive hand force modulation when interacting with a virtual object moving in the horizontal plane. We hypothesized that SPEM signals are critical for timing motor responses, anticipatory control of hand force, and task performance. Participants held a robotic manipulandum and attempted to stop an approaching simulated object by applying a force impulse (area under force-time curve) that matched the objects virtual momentum upon contact. We manipulated the objects momentum by varying either its virtual mass or its speed under free gaze or constrained gaze conditions. We examined gaze variables, timing of hand motor responses, anticipatory force control, and overall task performance. Our results show that when SPEM were constrained, anticipatory modulation of hand force prior to contact decreased. However, constraining SPEM did not seem to affect the timing of the motor response or the task performance. Together, these results suggest that SPEM may be important for anticipatory control of hand force prior to contact and may also play a critical role in anticipatory stabilization of limb posture when humans interact with moving objects. New and NoteworthyWe show for the first time that smooth pursuit eye movements (SPEM) play a role in modulation of anticipatory control of hand force to stabilize posture against contact forces. SPEM are critical for tracking moving objects, facilitate processing motion of moving objects, and are impacted during aging and in many neurological disorders, such as Alzheimers disease and Multiple Sclerosis. These results provide a novel basis to probe how changes in SPEM could contribute to deficient limb motor control in older adults and patients with neurological disorders.

neuroscience↗