Abstracts

Rationale: Intracranial electrocorticography (ECoG) recording is utilized in epilepsy centers, to localize brain areas generating spontaneous epileptiform discharges and to identify those activated in sensorimotor and cognitive tasks. In general, augmentation of task-related gamma-oscillations on ECoG (50 to 200 Hz) is considered to represent cortical activation elicited by a given task. We determined the spatio-temporal dynamics of cortical gamma-oscillations modulated during eye movement tasks, using simultaneous eye tracking and intracranial ECoG recording. Methods: Five patients with focal epilepsy (age range: 13 - 21 years; 3 females) were instructed to follow a target moving intermittently and unpredictably from one place to another either in an instantaneous or smooth fashion during extraoperative ECoG recording. In addition to the aforementioned eye movement task, patients were asked to read a single word popping up on the screen.Results: Target motion elicited augmentation of gamma-oscillations in the lateral, inferior and polar occipital regions in addition to portions of parietal and frontal regions; subsequent voluntary eye movements elicited gamma-augmentation in the medial occipital region. Such occipital gamma-augmentations could not be explained by contaminations of ocular or myogenic artifacts. The degree of gamma-augmentation was generally larger during saccade compared to pursuit trials, while a portion of the polar occipital region showed pursuit-preferential gamma-augmentations. Gamma-augmentation was elicited in widespread occipital regions following word presentation, while gamma-augmentation in the anterior portion of the medial occipital region was elicited by an involuntary saccade following word presentation rather than word presentation itself. Conclusions: Gamma-augmentation in the lateral, inferior and polar occipital regions can be explained by increased attention to a moving target, whereas gamma-augmentation in the anterior-medial occipital region may be elicited by images in the peripheral field realigned following saccades.