1. A method of modeling Transcranial Magnetic Stimulation (TMS) on a deep brain target, the method comprising: arranging representations of a plurality of TMS electromagnets around a model of a patient's head, wherein each TMS electromagnet has a pre-computed magnetic field model; calculating the intensity of the magnetic field at each of a plurality of brain regions by summing the magnetic field intensities of the portions of the pre-computed magnetic field model for each TMS electromagnet at each brain region; and displaying the calculated magnetic field intensities for each of the plurality of brain regions.