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Savings has been described as the ability of healthy humans to relearn a previously acquired motor skill faster than the first time, suggesting that the learning rate in the brain could be adjusted when a perturbation is recognized. Alternatively, it has been argued that apparent savings were the consequence of a distinct process that instead of reflecting a change in the learning rate, revealed an explicit re-aiming strategy. Based on recent evidence that feedback adaptation may be central to both planning and control, we hypothesized that there existed a feedback adaptation component that could genuinely accelerate the learning in the context of force field. We used a standard velocity-dependent force field paradigm consisting of adaptation-washout-readaptation phases with two groups of healthy volunteers. Each group performed the task with a randomly assigned force field direction (clockwise or counterclockwise). First, we found that readaptation was faster, confirming the presence of savings. Second and most importantly, we demonstrate that the very first readaptation movement displayed the characteristics of better-adapted movements to the perturbation, in the absence of any anticipation or explicit cognitive strategy. Specifically, the first readaptation trial has smaller path length, and higher correlation between commanded and applied forces, compared to the first adaptation trial. Additionally, we verified that the late washout trials were statistically indistinguishable from the baseline trials, suggesting that deadaptation was complete. That is, the online corrections in the first readaptation trial carried imprints of feedback adaptation from the previous sessions without any explicit strategy. Thus the feedback-mediated component contributes to savings in human reaching adaptation.We conclude that feedback adaptation is a medium by which the nervous system can genuinely accelerate learning across movements.

Combination of signals based on their reliability is an increasingly popular model for sensorimotor processing. However, how reliability is estimated, or how such estimation is affected by prolonged exposure to noisy inputs, is still unknown. In this study, we compare patients with unilateral functional amblyopia with control subjects tracking either a reliable target, or a blurry, unreliable target, in a task of repeated, sustained smooth pursuit. We provide evidence for a lower weight of visual information during smooth pursuit in amblyopic and control subjects tracking a blurry target, with no significant difference of prior information weight. In contrast, we found no evidence of lower visual information weight in the catch-up saccades of amblyopic subjects. We conclude that oculomotor performance in unilateral amblyopia mostly lays within the continuum between our control groups, without significant differences in the relative weights of prior and visual information. However, smooth pursuit exhibits additional deficits that might result from abnormal visual development. ispartof: MATHEMATICAL MODELLING IN MOTOR NEUROSCIENCE: STATE OF THE ART AND TRANSLATION TO THE CLINIC. OCULAR MOTOR PLANT AND GAZE STABILIZATION MECHANISMS vol:248 pages:45-63 ispartof: location:Univ Pavia, Pavia, ITALY status: published

There is growing evidence in the literature suggesting that sensori-motor deficits have a detrimental impact on cognitive abilities, such as the perception and representation of space. Most of the tasks classically used to assess spatial perception abilities after brain damage seem however not adequate to reveal potentially more discrete impairments in patients that are predominantly suffering from sensori-motor symptoms. To this aim we adapted the classic line bisection task in a virtual reality environment for the use with patients with upper-limb sensory-motor deficits. Here, we report the results from two pre-clinical experiments with healthy volunteers. Lines were projected horizontally on a semi-reflective mirror. Participants were asked to bisect the lines at their estimated midpoint by means of a robotic handle. Manipulated factors were the static hand, the position of the static hand (inside or outside of workspace), the visibility of the hands and the location of the lines. Results showed that participants neglected the most lateral part of the lines when they were projected distantly from the starting point. Bisection biases were in general more important when participants could see their hands. Additionally, participants took more time to initiate movements when they had to cover a short distance to reach the lines. We conclude that our robotic adaptation of the line bisection task was able to highlight subtle perceptual asymmetries in healthy individuals and that its use to reveal discrete cognitive deficits in patients with sensory-motor impairments seems therefore promising.