Experimentation with a transcranial magnetic stimulation system for functional brain mapping

Abstract

We describe functional brain mapping experiments 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). We have developed a system which not only generates functional brain maps using such a device, but also provides real-time feedback to guide the technician in placing the probe at appropriate points on the head for achieving the desired map resolution. Functional areas we have mapped are the motor and visual cortex. Validation experiments to date have consisted of repeatability and symmetry tests for mapping the same subjects several times. Applications of the technique include neuranatomy research, surgical planning and guidance, treatment and disease monitoring, and therapeutic procedures.