Electrical Stimulation Mapping of Brain Function: A Comparison of Subdural Electrodes and Stereo-EEG

Abstract

Despite 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. 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). There are two principal modalities for intracranial EEG, namely subdural electrodes and stereotactic depth electrodes (stereo-EEG). Although ESM is considered the gold standard for functional mapping with subdural electrodes, there have been concerns about its utility with stereo-EEG. 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. 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. 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. 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. We have also compared ESM with stereo-EEG and subdural electrodes, for current thresholds required to evoke desired functional responses vs. unwanted after-discharges. In this regard, there is preliminary evidence that ESM with stereo-EEG may be safer than ESM with subdural grids. 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.

Neural bases of the bodily self as revealed by electrical brain stimulation: A systematic review

“…Despite the recognized clinical advantages of EBS (George et al, 2020 ; Grande et al, 2020 ; Mandonnet et al, 2010 ), functional brain mapping using EBS has several limitations related to procedures and clinical constraints, which have been discussed in details elsewhere (Borchers et al, 2011 ; Parvizi & Kastner, 2018 ; Ritaccio et al, 2018 ).…”

“…EBS is typically used during presurgical evaluation of focal intractable epilepsy to define as accurately as possible the seizure onset zone and perform functional brain mapping (Trebuchon et al, 2020 ; Trébuchon & Chauvel, 2016 ), or in awake patients during brain tumor resection (Duffau, 2015 ). During EBS an electrical current of several mA is directly delivered to the brain through intracerebrally implanted electrodes (stereoelectroencephalography, SEEG) or through subdural grids and strips of electrodes placed at the surface of the cerebral cortex (electrocorticography, ECoG; Grande et al, 2020 ; Isnard et al, 2018 ; Lesser et al, 2010 ). SEEG electrodes are implanted either unilaterally or bilaterally, and each electrode has multiple contacts to record activity from several brain regions and/or to apply EBS (Isnard et al, 2018 ).…”

Functional Topography of Auditory Areas Derived From the Combination of Electrophysiological Recordings and Cortical Electrical Stimulation

“…In our view, solid physiological foundations underlying the effect of electrical stimulation need to be established, and the labeling of direct electrical stimulation as the “gold standard for mapping brain function” remains the matter of an interesting debate ( Grande et al, 2020 ).…”

Invasive EEG in non-lesional epilepsy

“…Der Vorteil des SEEG liegt dabei in der Erreichbarkeit tief gelegener Strukturen [12,19], die Nachteile in der geringeren flächigen Abdeckung des oberflächlichen Kortex und dem schwierigeren Mapping von eloquenten Hirnarealen [12]. Nichtsdestotrotz ist das Mapping von Sensorik, Motorik und Sprache auch mit SEEG-Elektroden möglich [6]. Ist die Hypothese zu ungenau formuliert oder die epileptogene Zone sehr klein, kann sie durch SEEG-Elektroden nicht detektiert werden.…”