Comparison of high gamma electrocorticography and fMRI with electrocortical stimulation for localization of somatosensory and language cortex

•Stimulation of the thumb and auditory semantic decision task were used in intracranial ECoG and fMRI.•The combination of hgECoG and fMRI increased the rate of patients with presurgical mapping results.•The contribution of parallel localization tools can make presurgical mapping more flexible.

ObjectiveWe investigated the contribution of electrocortical stimulation (ECS), induced high gamma electrocorticography (hgECoG) and functional magnetic resonance imaging (fMRI) for the localization of somatosensory and language cortex.Methods23 Epileptic patients with subdural electrodes underwent a protocol of somatosensory stimulation and/or an auditory semantic decision task. 14 Patients did the same protocol with fMRI prior to implantation.ResultsECS resulted in the identification of thumb somatosensory cortex in 12/16 patients. Taking ECS as a gold standard, hgECoG and fMRI identified 53.6/33% of true positive and 4/12% of false positive contacts, respectively. The hgECoG false positive sites were all found in the hand area of the post-central gyrus. ECS localized language-related sites in 7/12 patients with hgECoG and fMRI showing 50/64% of true positive and 8/23% of false positive contacts, respectively. All but one of the hgECoG/fMRI false positive contacts were located in plausible language areas. Four patients showed post-surgical impairments: the resection included the sites positively indicated by ECS, hgECoG and fMRI in 3 patients and a positive hgECoG site in one patient.ConclusionsHgECoG and fMRI provide additional localization information in patients who cannot sufficiently collaborate during ECS.SignificanceHgECoG and fMRI make the cortical mapping procedure more flexible not only by identifying priority cortical sites for ECS or when ECS is not feasible, but also when ECS does not provide any result.