Coaxial insulated bipolar electrode for monopolar and bipolar mapping of neural tissue: technical note with emphasis on the principles of intra-operative stimulation.

To facilitate use of various stimulation modes for intra-operative monitoring during neurosurgical procedures, we designed and produced a variable stimulation system that consists of a coaxial bipolar flush-tip insulated stimulation electrode, and a switch box to administer monopolar or bipolar stimulation through the same stimulation electrode. The electrode is composed of components that are readily available, so that its construction can be duplicated by others at minimal expense. For mapping of neural tissue during surgical procedures, we use the monopolar stimulation mode to identify relative large areas around the site of stimulation which are free of motor nerve fibres. The bipolar stimulation mode is most useful for precise localization of motor nerve fibres and in distinguishing motor from non-motor fibres.