Non-invasive functional brain mapping using registered transcranial magnetic stimulation

The authors describe a method for mapping the functional regions of the brain using a transcranial magnetic stimulation (TMS) device. This device, when placed on a subject's scalp, stimulates the underlying neurons by generating focused magnetic field pulses. A brain mapping is then generated by measuring responses of different motor and sensory functions to this stimulation. The key process in generating this mapping is the association of the 3D positions and orientations of the TMS probe on the scalp to a 3D brain reconstruction such as is feasible with a magnetic resonance image (MRI). The authors perform this matching process by (1) registering the subject's head position to an a priori MRI scan, (2) tracking the 3D position/orientation of the TMS probe, (3) transforming the TMS probe position/orientation to the MRI coordinate frame, and (4) tracking movements in the subject's head position to factor out any head motion. The resultant process generates a high resolution, accurate brain mapping which supports surgical planning, surgical guidance, neuroanatomy research, and psychiatric therapy. When compared to other functional imaging modalities, this approach exhibits much lower cost, greater portability, and more direct active control over the functional areas being studied.