Fig. 4: FEM was used to estimate EF strength in the rat spinal cord and assess effects of cord size variations.

a The generated EF was estimated by applying the finite element method (FEM) to a model of the rat’s spinal cord. b The longitudinal EF of the medium spinal cord is focused between the stimulation electrodes. c For the subdural implant, three different cord sizes were simulated (see dimensions in Table 2). At the midline of the simulated spine (ML) the longitudinal EF plateaus in the range of 0.8 to 1.6 mV/mm depending on the cord size over a distance of 4 mm, while it is weaker at the ventral line (VL, 1 mm ventral from ML) and stronger with peaks at the electrode positions at the dorsal line (DL, 1 mm dorsal from ML). The generated field strength decreases when moving the implant epidural.