Stereo-EEG mapping of visual working memory with task-related high-gamma modulations

Objective: We describe a safe, informative, and easy-to-implement approach for presurgical mapping of visual working memory (VWM) with stereo-electroencephalography (SEEG). Methods: Twenty-four patients with drug-resistant epilepsy, 11-23 years of age, performed a single-probe change detection VWM task, during SEEG monitoring. High-gamma modulations (HGMs) and connectivity modulations (weighted phase lag index) were computed for encoding, retention, recall, and response phases compared to a rest phase. Effects of lesioning sites with significant HGM on neuropsychological outcomes were analyzed. Results: Validity of our VWM task was evident by picture vocabulary scores covarying positively with increasing consistency and negatively with increasing maximum latency of the response times, respectively. VWM task elicited specific patterns of cortical HGMs during each phase: bilateral frontoparietal augmentation during encoding, replaced by widespread suppression during retention, followed by diffuse bilateral augmentation during the recall and response phases. Distinct neural circuits were also observed during each phase of the VWM task: left-lateralized phonological loop during encoding, short-range bilateral frontal connectivity during retention, and interhemispheric peri-Rolandic hubs during recall and response phases. Lesioning sites with significant high-gamma augmentation was associated with declines in domains directly relevant to VWM including working memory (slope -6.18,