The human brain is almost completely unreactive to magnetic fields. The trick with TMS is that it creates an extremely short pulse- a time varying field, which

The human brain is almost completely unreactive to magnetic fields. The trick with TMS is that it creates an extremely short pulse- a time varying field, which induces a voltage at the focal point of the field. This voltage is on the order of 100 mV, which is well in excess of what is needed to trigger all of the nerves in an area to fire. Static fields do not have the same effect unless you are moving through them at immense speed, eg passing from a region of 2 Tesla to 0 Tesla in a few milliseconds which would mean moving around the speed of sound through an MRI.