Although early ESM studies allowed some neuroanatomic generalizations based on convergence with lesion data, significant inter-individual variability in the location and extent of eloquent cortical regions was also realized ( Ojemann, 1979 Ojemann et al., 2003). Subsequent pioneering work of Penfield, Ojemann, and others, generated novel information about functional neuroanatomy and established electrical stimulation mapping (ESM) as the gold-standard for pre-surgical localization of eloquent cortical areas ( Penfield and Boldrey, 1937 Penfield and Jasper, 1954 Whitaker and Ojemann, 1977 Ojemann and Mateer, 1979 Jayakar et al., 2014). The muscles of the neck were thrown into action, and the head was strongly defected to the right”. He most likely stimulated the left supplementary sensorimotor area, and observed: “…arm was thrown out, the fingers extended, and the leg was projected forward. Finally, we have highlighted important unanswered clinical and scientific questions for ESM with stereo-EEG in the hope to encourage future research and collaborative efforts.Ī behavioral response to direct electrical stimulation of the human brain was first reported in 1874 from Cincinnati when Bartholow stimulated visible brain tissue in a 30-years-old woman whose parietal bone was eroded by a scalp epithelioma ( Bartholow, 1874). In this regard, there is preliminary evidence that ESM with stereo-EEG may be safer than ESM with subdural grids. We have also compared ESM with stereo-EEG and subdural electrodes, for current thresholds required to evoke desired functional responses vs. Emerging evidence shows that ESM for defining functional neuroanatomy is feasible with stereo-EEG, but probably requires a different approach for interpretation and clinical decision making compared to ESM with subdural electrodes. As stereo-EEG is increasingly the preferred modality for intracranial monitoring, we find it opportune to summarize the literature for ESM with stereo-EEG in this narrative review. Stereo-EEG, while having relatively sparse sampling on the cortical surface, offers the ability to access the depth of sulci, mesial and basal surfaces of cerebral hemispheres, and deep structures such as the insula, which are largely inaccessible to subdural electrodes. This is mainly because subdural electrodes allow contiguous sampling of the dorsolateral convexity of cerebral hemispheres, and permit delineation of the extent of eloquent functional areas on the cortical surface. Although ESM is considered the gold standard for functional mapping with subdural electrodes, there have been concerns about its utility with stereo-EEG. There are two principal modalities for intracranial EEG, namely subdural electrodes and stereotactic depth electrodes (stereo-EEG). This requires chronic monitoring with intracranial electroencephalography (EEG), which facilitates better localization of the seizure onset zone, and allows evaluation of the functional significance of cortical regions-of-interest by electrical stimulation mapping (ESM). 2Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH, United Statesĭespite technological and interpretative advances, the non-invasive modalities used for pre-surgical evaluation of patients with drug-resistant epilepsy (DRE), fail to generate a concordant anatomo-electroclinical hypothesis for the location of the seizure onset zone in many patients.1Division of Neurology, Comprehensive Epilepsy Center, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH, United States.
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