Figure 3.
Validation of PNM and ENM through experimental data
(A) Experimental data from Vallbo’s research studies43,44,45 on index flexion around the metacarpal-phalangeal joint is used for a reparameterization of Prochazka’s Ia fibers muscle spindle transducer model. The trials are subdivided randomly in training and validation sets. From the training set, joint angles are used to compute muscle fiber elongation and contraction velocities through NMS modeling; together with EMG activity they are used as input for the Prochazka model computation. RMSE minimization between the Ia predicted firing rate and experimentally recorded microneurography is performed to adapt model parameters to human data. Final validation of the modified model is performed on the validation set. See also Figure S1.
(B) Four electrodes were implanted in each of the two amputees. The perceptual thresholds and location of the sensation within a month from implantation are hereby reported.
(C) The modeled electrode placements on subject 1.
(D) QQ-plot of experimental and model thresholds.
(E) Histogram and boxplot of experimental and model thresholds. The range of injected charges associated with intrafascicular placements in the model is marked.
(F) Boxplot of ratio of intrafascicular active sites in model and in experiment (estimated using the same charge range) and an example of the experimental results for one electrode applied on the best fitting modeled placement.