Abstracts

Rationale: Non-epileptic eloquent cortices augment or suppress the amplitude of high-frequency oscillations (HFOs) of physiological nature either spontaneously or during a perceptual/behavioral task. Measurement of such event-related modulations of HFOs is useful to delineate the spatiotemporal dynamics of cortical activation and suppression involved in a given task. Here we studied saccadic suppression, which is a transient reduction of visual sensitivity during each of rapid eye movements and an essential mechanism underlying stable visual perception. We determined and animated the dynamics of saccade-related modulations of HFOs at 70-110 Hz at the whole brain level in a four-dimensional (4D) manner. Methods: We studied 12 patients (age: 6-20 years) who underwent extraoperative electrocorticography (ECoG) recording as a part of the presurgical evaluation of drug-resistant focal epilepsy. We limited the analysis to electrode channels which were outside the seizure onset zone, epileptogenic lesions, and irritative zone. We measured the percent change of the amplitude of HFOs time-locked to the onset and offset of 100 spontaneous saccade events during wakefulness, and delineated the dynamic modulations of HFOs on a standard three-dimensional surface image. We determined which of the striatal (summation of lingual and cuneus gyri), lateral-occipital, and fusiform regions would show a transient suppression and augmentation of HFOs before, during, and after saccades. Results: The resulting 4D map showed a transient suppression of HFOs in the lateral-occipital regions between saccade onset and offset, and subsequently showed a transient augmentation of HFOs in the striatal regions immediately following saccade offset. Conclusions: Saccade-related suppression of HFOs in the lateral-occipital regions may be at least in part responsible for saccadic suppression. Greater HFO suppression in the lateral-occipital region contralateral to the direction of saccades is consistent with the notion that saccade suppression maximally takes place in the attended visual field. Correlation of ECoG signals with saccade events may reduce the risk of misinterpretation of physiological HFOs as pathological. Funding: No funding