Occipital gamma-oscillations modulated during eye movement tasks: Simultaneous eye tracking and electrocorticography recording in epileptic patients

Abstract

We determined the spatio-temporal dynamics of cortical gamma-oscillations modulated during eye movement tasks, using simultaneous eye tracking and intracranial electrocorticography (ECoG) recording. Patients with focal epilepsy 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. 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. In addition to the aforementioned eye movement task, patients were asked to read a single word popping up on the screen. 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. 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. In functional studies comparing brain activation between two tasks, eye movement patterns during tasks may need to be considered as confounding factors.

Direct recordings in human cortex reveal the dynamics of gamma-band [50–150Hz] activity during pursuit eye movement control

“…The late onsets of neural activity in MOG and CUN that followed target motion onset, are consistent with a previous report and confirm that occipital activity propagate from lateral to medial occipital sites during pursuit (Nagasawa et al, 2011).…”

“…In the pursuit FEF, gamma band activity was higher during RP than during PI, indicative of a role in pursuit maintenance, whereas the saccade FEF was characterized by a transient gamma activity that is consistent with the pattern of gamma activity observed in the two previous FEF direct recordings (Lachaux et al, 2006;Nagasawa et al, 2011). Gamma power was higher during reactive compared to predictive pursuits in saccade FEF, perhaps because during RP, more saccades occurred in this study.…”

Continuous High Frequency Activity: A peculiar SEEG pattern related to specific brain regions

“…Other studies performed with electrocorticography described gamma band augmentation during eye movement tasks (Nagasawa et al, 2011); during photic stimuli, a high-gamma augmentation was most prominent in the medial occipital region (Matsuzaki et al, 2012). It is not clear if the evoked gamma activity evaluated by these studies is related to the spontaneous continuous HFA reported in our study.…”

Cortical representation of persistent visual stimuli

“…The finding of duration-tracking responses could be potentially explained as the temporally summed activity of transient (onset) responses to retinal shifts driven by eye movements (EM) while the stimulus is presented (Nagasawa et al, 2011). However, there are good reasons to suggest that duration-tracking responses are not merely driven by EM.…”