Electrical impedance recording for localization in functional neurosurgery of the spinal cord and lower brain stem

Functional neurosurgery aims to modify or abolish neural messages. Established techniques use confirmatory electrical stimulation prior to ablation and require local anesthesia. Recently developed procedures take place under general anesthesia increasing the chance of damage to adjacent neural structures with postoperative morbidity. We describe a laboratory study correlating changes in measured electrical impedance with transition from white to grey matter in the brain and spinal cord of two mammalian species; this has not previously been easy to undertake, nor felt reliable. Impedances can now be measured simply and reliably. This study confirms our operating theater experience. We recommend that when stimulation cannot be used, impedance can and should be utilized to indicate the need for an electrode to be resited.