The location of action potential initiation and the magnetic threshold depend on the location of the soma relative to the coil.

A, A soma with a long straight axon containing sections of myelin and nodes of Ranviar was located in a plane below the coil. Soma, axon and node diameters were 20 µm, 1 µm and 0.75 µm, respectively. Soma, axon and nodes lengths were 20 µm, 100 µm and 1 µm, respectively. The view from above shows that the artificial neuron was shifted along the y-axis by one coil radius and along the x-axis by Δx. B, The magnetic threshold decreased with Δx until it reached a minimum at the location corresponding to the maximal gradient of the electric field. The action potential was initiated at the axon for small shifts (Δx<0.05 cm, green dots), and at the soma for larger shifts (black dots). The lowest magnetic threshold was achieved when the soma was located at the largest gradient of the induced electric field.