Biology subjects

Schweighofer, N.

Publications and source records attributed to Schweighofer, N..

3 recordsLinked to original sources

bioRxiv2018

Dosage Matters: A Randomized Controlled Trial of Rehabilitation Dose in the Chronic Phase after Stroke

Background and PurposeFor stroke rehabilitation, task-specific training in animal models and human rehabilitation trials is considered important to trigger inherent neuroplasticity, promote motor learning, and functional recovery. Little is known, however, about what constitutes an effective dosage of therapy.\n\nMethodsThis is a parallel group, four arm, single blind, phase I, randomized control trial of four dosages of upper extremity therapy delivered in an outpatient setting during the chronic phase after stroke. Participants were randomized into groups that varied in total dosage of therapy (i.e., 0, 15, 30, or 60 hours). Seven hundred and four participants were assessed for eligibility, 50 were eligible to enroll, 45 were randomized, 44 participated and 41 completed the study. Planned primary analyses used linear mixed effects regression to model baseline to post-intervention changes in the Motor Activity Log-Quality of Movement rating (MALQ) and the Wolf Motor Function Test (WMFT) time score as a function of therapy dosage. A series of hierarchical models were constructed using the MALQ and WMFT.\n\nResultsWe observed a significant dose response curve: the greater the dosage of training, the greater the change in MALQ, with the dose by week slope parameter of 0.0045 ({Delta}MAL/hour/week; p = 0.0011; 95% CI = [0.0019; 0.0071]). Over the 3 weeks of therapy, this corresponds to a gain of 0.81 in MALQ for the 60 hour dose.\n\nConclusionsFor mild-to-moderately impaired stroke survivors, the dosage of a patient-centered, task specific motor therapy was shown to systematically influence the gain in quality of arm use in the natural environment, but not functional capacity as measured in the laboratory. We highlight the importance of recovery outcomes that capture arm use vs. functional capacity.\n\nClinical Trial RegistrationURL: http://www.clinicaltrials.gov. Unique identifier: NCT 01749358

clinical trials↗

bioRxiv2018

To Overwrite or to Recall? Individual Differences in Motor Adaptation

The central nervous system predicts the consequences of motor commands by leaning multiple internal models of external perturbations and of the body. It is not well understood, however, how new internal models are created. Here, we propose a novel computational model of motor adaptation in which a stochastic Bayesian decision-making process determines whether i) a previously updated expert perturbation model is recalled and updated, ii) a novice model is selected and is updated into a new expert, or iii) the \"body\" model is updated. Results from computer simulations provide insights into various and contradictory experimental data on savings and error-clamp, and predicts qualitative individual differences in adaptation. We verified these predictions in a visuomotor adaptation experiment in which we varied the perturbation amplitudes as well as the amount of noise added to perturbation, and added \"trigger\" trials in the error-clamp condition. Single trigger trials led to largely qualitatively different behavior and can therefore be used to probe individual differences in memory updates between \"one-model\" and \"two-model\" learners. \"One-model\" learners continuously update the body model, showing no savings during re-adaptation to the perturbation, and gradual decay during error clamp. In contrast, \"two-model\" learners switch between an updated expert model and the body model, showing large savings during re-adaptation and stochastic lags during error clamp. Our results thus support the view that motor adaptation belongs to the general class of human learning according to which new memories are created when no existing memories can account for discontinuities in sensory data.\n\nShort summary/significanceWhen movements are followed by unexpected outcomes, such as following the introduction of a visuomotor or force field perturbation, or the sudden removal of such perturbations, it is unclear whether the central nervous system updates existing memories or creates new memories. Here, we propose a novel model of adaptation, and investigate, via simulation and behavioral experiments, how the amplitude and schedule of the perturbation, as well as the characteristics of the learner, lead to updates of existing memories or creation of new memories. Our results provide insights into a number of puzzling and contradictory experimental data on savings and error-clamp, as well as large qualitative individual differences in adaptation.

neuroscience↗

bioRxiv2018

What you predict, not what you do, updates memories in visuomotor adaptation

Sensory prediction errors are thought to update memories in motor 1 adaptation, but the role of performance errors is largely unknown. To dissociate these errors, we manipulated visual feedback during fast shooting movements under visuomotor rotation. Participants were instructed to strategically correct for performance errors by shooting to a neighboring target in one of four conditions: following the movement onset, the main target, the neighboring target, both targets, or none of the targets disappeared. Participants in all conditions experienced a drift away from the main target following the strategy. In conditions where the main target was shown, participants often tried to minimize performance errors caused by the drift by generating corrective movements. However, despite differences in performance during adaptation between conditions, memory decay in a delayed washout block was indistinguishable between conditions. Our results thus suggest that, in visuomotor adaptation, sensory predictions errors, but not performance errors, update the slow, temporally stable, component of motor memory.

neuroscience↗