A review of neurophysiological mapping procedures of the brain and spinal cord

Surgical procedures of the brain and spine that require manipulation of, and near nervous structures, require unique considerations in their approach. Over the past 100 years, techniques have been developed and refined for localization of specific structures allowing for safer, more accurate interventions. These include the pre-operative use of Electroencephalography (EEG) in combination with radiographical imaging and intraoperative neurophysiological techniques rooted in electrophysiology. Since the introduction of EEG and electrical cortical stimulation, physicians have had the tools to diagnose neurological conditions while also being able to complete surgical interventions with a level of safety. By the 1920’s and 1930’s, the efforts of Hans Berger and Frederic and Erna Gibbs to develop and utilize EEG led to accurate pre-operative diagnoses of epilepsy along with their associated foci. Within that same time, the efforts of Wilder Penfield to develop and implement electrical cortical stimulation in awake patients during neurosurgery led to broad understandings of the organization and function of regions of the brain. Both EEG and cortical stimulation in combination quicky became useful beyond research in mapping the regions of the brain and led to rapid improvements in the accuracy of epilepsy surgery. Over preceding decades, these techniques continued to evolve with the latest research and technology. Additionally, their utilization has expanded from epilepsy surgery to resection for neoplasms of the central nervous system. In contemporary surgery, EEG and cortical stimulation still serve as the backbone of mapping techniques, but novel techniques are continually explored and improve patient outcomes. These advances include modern intraoperative neurophysiological monitoring, improved stimulation techniques, and additional utilization beyond the brain. This review highlights the conceptual underpinning of electrical neurophysiological mapping techniques as well as their implementation and future considerations. The review covers the pre-operative mapping of the brain using EEG, intraoperative mapping of the brain using cortical and subcortical mapping, and spinal cord mapping of the dorsal column and anterolateral tracts. The techniques and theory of each are summarized along with discussions on implementation and efficacy. Additional emphasis is placed on the need for standardization of their use to improve patient outcomes and recommendations for future research and development