Methodology for non-invasive mapping of human motor cortex with electrical stimulation.

Different techniques for mapping motor evoked potentials recorded from hand, upper arm, leg and mouth were analyzed. The best results were obtained when: (1) delivering constant voltage stimuli through a bipolar surface stimulator, (2) positioning the anode over the desired scalp location and the cathode 2.5 cm anterior to the anode, (3) maintaining low impedances, and (4) increasing the stimulus intensity over the theoretical motor representation area until a 500-1000 microV muscle response is achieved and then delivering the same stimulus over different scalp locations. This technique allows bilateral mapping of the different body part representations in 1-2 h. Areas so identified are small, clearly separate from each other and from the corresponding somatosensory areas.