Abstract
About one third of patients with epilepsy have seizures refractory to the medical treatment. Electrical stimulation mapping (ESM) is the gold standard for the identification of “eloquent” areas prior to resection of epileptogenic tissue. However, it is time-consuming and may cause undesired side effects. Broadband gamma activity (55–200 Hz) recorded with extraoperative electrocorticography (ECoG) during cognitive tasks may be an alternative to ESM but until now has not proven of definitive clinical value. Considering their role in cognition, the alpha (8–12 Hz) and beta (15–25 Hz) bands could further improve the identification of eloquent cortex. We compared gamma, alpha and beta activity, and their combinations for the identification of eloquent cortical areas defined by ESM. Ten patients with intractable focal epilepsy (age: 35.9 ± 9.1 years, range: 22–48, 8 females, 9 right handed) participated in a delayed-match-to-sample task, where syllable sounds were compared to visually presented letters. We used a generalized linear model (GLM) approach to find the optimal weighting of each band for predicting ESM-defined categories and estimated the diagnostic ability by calculating the area under the receiver operating characteristic (ROC) curve. Gamma activity increased more in eloquent than in non-eloquent areas, whereas alpha and beta power decreased more in eloquent areas. Diagnostic ability of each band was close to 0.7 for all bands but depended on multiple factors including the time period of the cognitive task, the location of the electrodes and the patient’s degree of attention to the stimulus. We show that diagnostic ability can be increased by 3–5% by combining gamma and alpha and by 7.5–11% when gamma and beta were combined. We then show how ECoG power modulation from cognitive testing can be used to map the probability of eloquence in individual patients and how this probability map can be used in clinical settings to optimize ESM planning. We conclude that the combination of gamma and beta power modulation during cognitive testing can contribute to the identification of eloquent areas prior to ESM in patients with refractory focal epilepsy.
Highlights
Invasive cortical mapping for the precise characterization of “eloquent” cortical areas is necessary to minimize neurological or cognitive complications following resection of pathological tissue
We represented the change in power spectral density, relative to the baseline period (−0.7 to −0.1 s from sound onset) across time of the ECoG signal during each epoch of the delayed match-to-sample (DMTS) task (Figure 1B)
Using advanced signal analysis in combination to functional and attentional specific analysis we have shown that including alpha and especially beta power modulations from a DMTS task can improve the diagnostic ability in the identification of eloquent cortical areas over the use of gamma-band power alone
Summary
Invasive cortical mapping for the precise characterization of “eloquent” cortical areas is necessary to minimize neurological or cognitive complications following resection of pathological tissue. ESM is time consuming, requiring individual testing of each implanted electrode-contact, restricting the number of electrodes that can be tested and precluding the use of high density arrays (Bouchard et al, 2013; Mesgarani et al, 2014; Muller et al, 2016) thereby limiting the spatial resolution of ESM (Hermiz et al, 2018) These and other factors motivate the search for alternative ways to identify eloquent cortex (Crone et al, 2006, 1998a,b; Brunner et al, 2009; Lachaux et al, 2007; Vansteensel et al, 2010)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
