Vectrial magnetic stimulation of the human brain

We have developed a method of focal and vectorial magnetic stimulation. The basic idea is to concentrate induced eddy currents in a target by a pair of opposing pulsed magnetic fields which can be produced by a figure-of-eight coil. Since the concentrated eddy currents at the target beneath the intersection of the coils flow in the direction parallel to the tangent of the two circular coils, vectorial stimulation can be achieved. The neural fibers can be excited easily when the fivers are stimulated by the eddy currents which flow parallel to the neural fivers. Based upon this principle, we have obtained functional maps of the human motor cortex related to the hand and foot areas. We have observed that an optimal direction of stimulating currents for neural excitation exists in each functional area in the cortex. To explain these vectorial characteristics in magnetic brain stimulation, we developed a model of neural excitation elicited by magnetic stimulation. The model explains our observation that the direction of the induced current vectors reflect both the functional and anatomical organization of neural fibers in the brain.