Abstracts

Rationale: Visuospatial memory is an important function which is frequently assessed in evaluation of patients with drug-resistant focal epilepsy. Yet, no standardized methods have been established for localization of such function in children undergoing epilepsy surgery. We explored if measurement of high-gamma activity on intracranial electrocorticography (ECoG) during a game play session can localize the cortical regions involved in visuospatial memory. Methods: Extraoperative ECoG recording was performed to localize the epileptogenic zone and eloquent areas as part of clinical management of drug-resistant focal epilepsy. High-gamma activity at 70-110 Hz was measured during five sessions of game play (Lumosity; Lumos Labs, Inc, San Francisco, CA). Thereby, augmentation of high-gamma activity was treated as a biomarker of in-situ cortical activation. 'Memory Matrix' was chosen as a spatial short-term memory task, in which users are presented visual stimuli consisting of pattern of squares on a grid and recall the location of squares following a delay. We determined the spatial-temporal pattern of high-gamma modulation (i) at the onset of presentation of square stimuli, (ii) during encoding visuospatial memory, and (iii) at the onset of initial recall response by finger tapping on a tablet screen. Results: At the onset of presentation of square stimuli, high-gamma augmentation involved the lingual and fusiform gyri. Subsequently, during the encoding phase, high-gamma augmentation involved the Rolandic hand-motor area, supplementary motor area, and middle-frontal gyrus. At the same time, high-gamma attenuation involved the superior-temporal gyrus. Finally, at the onset of initial recall response, high-gamma augmentation involved the Rolandic hand-sensorimotor area. Trials with larger memory loads were associated with more intense attenuation of high-gamma activity in the superior-temporal gyrus. Conclusions: Measurement of event-related high-gamma modulation on ECoG is feasible using a tablet computer program. The cortical regions showing high-gamma augmentation during the encoding phase may reflect the network involved in visuospatial memory processing. Particularly, activation of Rolandic hand motor area, which was not previously emphasized in functional MRI studies, may be associated with the practice of a pointing procedure providing efficient memory performance. Larger memory loads in visual domain may result in greater suppression of the auditory cortex during the memory encoding phase. Funding: Grant support: R01NS064033 to E. Asano.