Explicit Action Switching Interferes with the Context-Specificity of Motor Memories in Older Adults

Aucie²,

Sargent

et al. 2019

Preprint

Self Cite

Section: Discussionsupporting

confidence: 89%

Motorized shoes induce robust sensorimotor adaptation in walking

Aucie²,

Sargent

et al. 2019

Preprint

Self Cite

“…Moreover, we find that incline split-belt walking leads to faster adaptation. This could be 806 exploited to increase the adaptation rate in older populations (Sombric et al, 2017), which 807 could benefit the training of older clinical populations. Our results also indicate that baseline 808 features of individual subjects are informative about subject-specific capacity to modify their 809 gait and learn new walking patterns, which is critical for understanding inter-subject differences 810 in motor corrections post-stroke.…”

mentioning

confidence: 99%

Large propulsion demands increase locomotor learning at the expense of step length symmetry

Sombric

Calvert

2018

Preprint

Self Cite

There is a clinical interest in increasing the extent of locomotor learning induced by split-belt treadmills that move each leg at different speeds. However, factors facilitating locomotor learning are poorly understood. We hypothesized that augmenting the braking forces, rather than propulsion forces, experienced at the feet would increase locomotor adaptation and learning. To test this, forces were modulated during split-belt walking with distinct slopes:inclined (larger propulsion than braking), declined (larger braking than propulsion), and flat (similar propulsion and braking). These groups were compared using step length asymmetry, which is a clinically relevant measure robustly adapted on split-belt treadmills. Unexpectedly, the group with larger propulsion demands (i.e., the incline group) adapted faster and more, and had larger after-effects when the split-belt perturbation was removed. We also found that subjects who propelled more during baseline and experienced larger disruptions of propulsion forces in early adaptation exhibited greater after-effects, which further highlights the catalytic role of propulsion on locomotor learning. The relevance of mechanical demands on shaping our movements was also indicated by the steady state split-belt behavior, during which each group recovered their baseline leg orientation to meet leg-specific force demands at the expense of step length symmetry. Notably, the flat group was nearly symmetric, whereas the incline and decline group overshot and undershot symmetry, respectively. Taken together, our results indicate that forces propelling the body facilitate gait adaptation during split-belt walking.Therefore, interventions that increase propulsion demands may be a viable strategy for augmenting locomotor learning in individuals with hemiparesis. 1999), reducing walking speed (Balasubramanian et al., 2007), compromising balance (Lewek et 47 al., 2014), and if not corrected, step length asymmetry leads to other comorbidities such as 48 musculoskeletal injuries (Jørgensen et al., 2000) and joint pain (Patterson et al., 2012). 49Promising studies have shown that walking with the legs moving at different speeds (i.e., split-50 belt walking) results in long-lasting reduction of step length asymmetry post-stroke when 51 walking overground (Reisman et al., 2009(Reisman et al., , 2013. However, split-belt walking is not always 52 effective even after repeated exposure to the split-belt experience (Reisman et al., 2013; Lewek 53 et al., 2017) and it is still unclear why some stroke survivors re-learn to walk symmetrically but 54 others do not. Thus, it is fundamental to identify factors facilitating split-belt adaptation to 55 augment them for increasing motor learning in all individuals. 56The increased mechanical work (Selgrade et al., 2017), step length asymmetry (Reisman 57 et al., 2005), and hence metabolic effort (Finley et al., 2013), upon introducing the split-belt 58 environment are thought to drive locomotor adaptation. Notably, these three factors are l...

“…Finally, StepVelocity was defined as the difference between the legs in terms of velocity of the foot with respect to the body when in contact with the ground. All parameters were expressed in units of distance and they were normalized to the sum of left and right step lengths in order to account for differences in step sizes across subjects (Sombric et al, 2017).…”

Section: Discussionmentioning

confidence: 99%

Cerebral contribution to the execution, but not recalibration, of motor commands in a novel walking environment

Kam

Iturralde

2019

Preprint

Human movements are flexible as they continuously adapt to changes in the environment by updating planned actions and generating corrective movements. Planned actions are updated upon repeated exposure to predictable changes in the environment, whereas corrective responses serve to overcome unexpected environmental transitions. It has been shown that corrective muscle responses are tuned through sensorimotor adaptation induced by persistent exposure to a novel situation. Here, we asked whether cerebral structures contribute to this recalibration using stroke as a disease model. To this end, we characterized changes in muscle activity in stroke survivors and unimpaired individuals before, during, and after walking on a split-belt treadmill moving the legs at different speeds, which has been shown to induce recalibration of corrective responses in walking in healthy individuals. We found that the recalibration of corrective muscle activity was comparable between stroke survivors and controls, which was surprising given then known deficits in feedback responses post-stroke. Also, the intact recalibration in the group of stroke survivors contrasted the patients' limited ability to adjust their muscle activity during steady state split-belt walking compared to controls. Our results suggest that the recalibration and execution of motor commands in new environments are partially dissociable: cerebral lesions interfere with the execution, but not the recalibration, of motor commands upon novel movement demands.