Functional mapping of the human motor cortex obtained by focal and vectorial magnetic stimulation of the brain

Functional mapping of the human motor cortex related to the hand and foot area was carried out using focal magnetic stimulation of the brain. The basic idea of localized brain stimulation is to concentrate induced eddy currents locally in the vicinity of a target by a pair of opposing pulsed magnetic fields. A figure-eight coil was positioned outside the head so that time-varying magnetic fields could pass through the head in opposite directions around a target. It was observed that an optimum direction of stimulating currents for neural excitation exists in each functional area in the cortex. The functional maps of the brain were sensitive to change in the direction of the stimulating currents. The experimental results suggest that the direction of current vectors for neural excitation in magnetic brain stimulation reflects both the anatomical and the functional organization of neural fibers in the brain.>