Abstracts

Rationale: On scalp EEG, posterior alpha activity is augmented with eye closure and suppressed with eye opening, as initially reported by Berger in 1929. Lambda activity, a triangular-shaped transient associated with saccadic eye movements, takes place over the bilateral posterior head regions, as originally written by Evans in 1952. While such eye movement-related neural activities are suggested to originate from the primary visual cortex, not many intracranial studies have visualized the spatiotemporal dynamics of spectral changes induced by spontaneous eye movements. The present study aimed to visualize the origin and propagation of intracranially-recorded alpha and high-gamma activities modulated by eye movements. High-gamma augmentation is an excellent surrogate marker of local cortical activation supporting given sensorimotor or cognitive function. In contrast, alpha activity is reported to be often suppressed when high-gamma activity is augmented.

Methods: We studied 33 patients (age: 5-20 years) who underwent intracranial EEG (iEEG) and electrooculography (EOG) recordings. Time-frequency analysis computed eye movement-related alpha (8-12 Hz) and high-gamma (70-110 Hz) amplitudes at 2,290 nonepileptic electrode sites, defined as those outside the seizure onset, spiking, and lesional sites. We generated the group-level atlases animating the spatiotemporal dynamics of alpha and high-gamma modulations on a three-dimensional standard surface image (Fig. 1, Fig. 2).

Results: [Eye closure] The posterior striate cortex showed high-gamma suppression and alpha augmentation within 100 ms after eye closure onset. Such spectral changes were subsequently noted in the fusiform cortex. High-gamma augmentation emerged in the bilateral anterior striate cortex within 300 ms after eye closure onset (Fig. 1A). [Eye opening] Over the striate cortex, high-gamma augmentation occurred within 100 ms after eye opening onset and alpha suppression within 200 ms. Such spectral changes were subsequently noted in the fusiform cortex (Fig. 1B). [Saccades] High-gamma suppression and alpha augmentation took place over the striate cortex during saccades. Such spectral changes were later observed in the fusiform cortex. The posterior striatal cortex showed intense high-gamma suppression and alpha augmentation lasting even after saccade offset. Conversely, the anterior striate cortex began to show high-gamma augmentation and alpha suppression at saccade offset (Fig. 2).

Conclusions: Eye closure, eye opening, and saccadic eye movements elicited iEEG spectral changes initially in the primary visual cortex and subsequently in the higher-order visual areas. Eye movement-related high-gamma augmentation generally co-occurred with alpha suppression, whereas high-gamma suppression with alpha augmentation. Anterior striatal high-gamma augmentation after eye closure may account for the notion that attention may be distributed to peripheral fields during eye closure. Intense and lingering saccade-related high-gamma attenuation in the posterior striatal regions may be the underlying mechanism of stable perception by transiently reducing foveal visual sensitivity during saccades.

Funding: Please list any funding that was received in support of this abstract.: NIH grant NS064033.