a, Model layout of the hybrid rat-human computational model used to tune the human neural network weights. W1, w2, w3 and w4 represent the weights of the neural network connections that have been modified to adapt the rat neural network to the human one. b, Systematic search results. W1 and w3 were ranged together between 1 and 2 times the weight used in the rat network, while w2 and w4 were ranged between 1 and 4 times. Bar plots report the percentage of simulations that fulfilled the defined fitness criteria. Selected weights that have been used for further simulations are highlighted with an arrow. c, Effect of EES on the natural activity of Ia-inhibitory interneurons and on the production of motor patterns during locomotion, in the hybrid rat-human model for the selected set of synaptic weights. Panels on the left report the average firing rate profiles of the Ia-inhibitory interneuron populations associated to either the flexor or the extensor network, as well as their modulation depth (mean ± SEM, n = 11 gait cycles). Similarly, right-most panels represent the average firing rate profiles of motoneurons and their mean firing rate activity during the phase in which they are active (mean ± SEM, n = 11 gait cycles). Effects of different EES frequencies and amplitudes are reported on the top and bottom panels, respectively.