A model for focal magnetic brain stimulation

In this study, we describe a magnetic coil designed for focal brain stimulation. We determined the distribution of magnetically induced currents using a multi-concentric spherical cranial computer model. The induced currents were primarily linearly oriented and concentrated below the coil's center. In comparison with large coils, small coils were less efficient but produced a more concentrated current distribution. Variations in conductivity among brain, scalp and skull produced secondary currents that reduced the magnetically induced current. This reduction in magnetically induced current was greater for larger coils.