Perisaccadic Occipital EEG Changes Quantified with Wavelet Analysis

Abstract

A role for the visual cortex in the dynamic interaction of saccades and visual processing is suggested by functional MRI studies, which reveal saccade-related striate (occipital) cortical activity. 1-6 Little is known, however, of the timing relationship between occipital changes and saccades. Occipital changes preceding the eye movement may be consistent with the notion of corollary discharge, 7,8 whereas occipital activity following the eye movement could signify the response of the visual cortex to a new, shifted visual field. In order to study the time course of occipital activity, we have studied electroencephalographic recordings in association with saccades. We concentrated on gamma range EEGs. It is known that gamma range activity represents local circuit binding of neurons engaged in the same task. 9 Our hypothesis was that there is a lawful relationship of gamma range occipital EEGs in relation to saccade timing and direction as the result of reorganization of neuronal binding in the visual cortex in association with saccades. Our hypothesis was based on the explicit suggestion of Morrone, Ross, and Burr 10 that visual space compression occurs during the short duration of a saccade. Previous studies of perisaccadic EEG changes 11,12 applied Fourier analysis, which is not adequate to quantify short-term EEG changes. Additionally, we concentrated on gamma range activity, as frequencies substantially lower could not be used by the brain to convey information of the chronology of neuronal reorganization during a saccade.Ten normal subjects were studied in comparable age range, with the mean age being 38 years. The EOG and infrared eye scan recorded self-paced saccades and eye position. Permanent markers were located 78 cm from the observer, their distance subtending 60 degrees at the eye. Fourteen channels of EEGs were recorded over posterior occipital and parietal channels. Following a test session, the continuous recording EEG and eye movement recordings were visually inspected, and with our software, cursors were placed, bracketing acceptable saccades. Saccades were marked when their velocity exceeded 200 degrees/second, and they were free of ret-

The coincidence between late non-phase-locked gamma synchronization response and saccadic eye movements

“…1, after filtering in gamma band there are discernable high frequency bursts on EEG which do not correspond to wave packets on vertical electrooculogram (vEOG) or horizontal electrooculogram (hEOG). To date there are only few evidences indicating putative association of saccadic eye movements with increased perisaccadic EEG gamma activity (Smyrnis et al, 2001;Bodis-Wollner et al, 2002;Sokolov et al, 2002).…”

“…Nonetheless, for the aimed analysis of the relationship between saccades and gamma band activity specially designed investigations are needed with more optimal stimuli (e.g. Bodis-Wollner et al, 2002) and finer measurements techniques (e.g. infrared beams or video recordings) to detect saccadic movements in a reliable way.…”

Cortical control of saccades in Parkinson disease and essential tremor

“…Contrary to the healthy subject, there was no evidence of intrasaccadic gamma power increase in PD patients. Bodis-Wollner et al (2002) and Forgacs et al (2008) described posterior perisaccadic gamma modulation associated with voluntary saccades. The results suggested a lack of modulatory coupling between frontal and posterior parietal circuits.…”

“…A blood oxygenation level-dependent (BOLD) study supports that specific, saccade direction-linked locations are activated in the map of the striate cortex when saccades are executed (Rieger et al 2008b). The scalp recorded EEG, shows parieto-occipital intrasaccadic increase in gamma (35-45 Hz) power when healthy human subjects execute self-initiated voluntary saccades (Bodis-Wollner et al 2002). In healthy subjects, gamma power increases during the saccade.…”

“…However, the primary visual cortex is not, while FEF is activated when eye movements are only imagined. The scalp recorded EEG, shows parieto-occipital intrasaccadic increase in gamma (35-45 Hz) power in healthy human subjects when executing self-initiated voluntary saccades (Bodis-Wollner et al 2002). The power increases during the saccade.…”