Development of distance-selective nerve recruitment for subcortical brain mapping by controlling stimulation waveforms

During brain surgery, it is important to determine the functional brain area and cortico-cortical pathways so as to keep them intact and preserve patients´ quality of life. Cortical and subcortical brain mappings are techniques that deliver direct current stimulation to the brain surface and beneath gray matter to identify the brain area and nerve fibers related to higher-order functions. However, because of the non-selective effect of conventional electrical stimulation methods, it has been difficult to obtain precise spatial distribution of nerve fibers in the subcortical region. We investigated the electrical stimulation of subcortical mapping to evaluate axon-to-electrode distance-selectivity. It was clarified that a conventional rectangular biphasic pulse activates axons non-selectively. We propose double exponential waveforms and show that they can recruit targeted fibers and change the location of a target by manipulating stimulus intensity. These results suggest the usefulness of introducing distance-selective stimulation into subcortical brain mapping.