Perisaccadic Parietal and Occipital Gamma Power in Light and in Complete Darkness

Abstract

Our objective was to determine perisaccadic gamma range oscillations in the EEG during voluntary saccades in humans. We evaluated occipital perisaccadic gamma activity both in the presence and absence of visual input, when the observer was blindfolded. We quantified gamma power in the time periods before, during, and after horizontal saccades. The corresponding EEG was evaluated for individual saccades and the wavelet transformed EEG averaged for each time window, without averaging the EEG first. We found that, in both dark and light, parietal and occipital gamma power increased during the saccade and peaked prior to reaching new fixation. We show that this is not the result of muscle activity and not the result of visual input during saccades. Saccade direction affects the laterality of gamma power over posterior electrodes. Gamma power recorded over the posterior scalp increases during a saccade. The phasic modulation of gamma by saccades in darkness--when occipital activity is decoupled from visual input--provides electrophysiological evidence that voluntary saccades affect ongoing EEG. We suggest that saccade-phasic gamma modulation may contribute to short-term plasticity required to realign the visual space to the intended fixation point of a saccade and provides a mechanism for neuronal assembly formation prior to achieving the intended saccadic goal. The wavelet-transformed perisaccadic EEG could provide an electrophysiological tool applicable in humans for the purpose of fine analysis and potential separation of stages of 'planning' and 'action'.

Human occipital cortices differentially exert saccadic suppression: Intracranial recording in children

“…Thus, it is likely that such gamma-augmentation partly reflects the early visual processing of fixed visual scenes provided at the offset of each saccade. Smaller but still significant saccade-related gamma-augmentation was noted in the medial and inferior occipital regions even during REM sleep in the present study, as similarly reported in a scalp EEG study conducted in complete darkness during wakefulness (Forgacs et al, 2008). A feasible explanation for these observations is that scanning of the internal visual imagery might elicit such occipital gamma-augmentation.…”

“…Studies of healthy humans using functional MRI (fMRI) and positron emission tomography (PET) failed to demonstrate consistent neural correlates of saccadic suppression; the occipital pole could be deactivated (Wenzel et al, 2000), unchanged (Kleiser et al, 2004) or even activated (Law et al, 1998; Sylvester et al, 2005) by saccades in darkness. Scalp EEG studies have not reported evidence of transient suppression of the human occipital activity during saccades (Forgacs et al, 2008). Studies of monkeys using microelectrode recording demonstrated transient reduction in firing rates, at the population level, in the superior colliculus (Ibbotson et al, 2008), lateral geniculate nucleus (Reppas et al, 2002; Saul, 2010), the primary visual cortex (V1) in the occipital lobe (Duffy and Burchfiel, 1975; Kagan et al, 2008; Rajkai et al, 2008), as well as portions of the temporal and parietal lobes (Ringo et al, 1994; Bremmer et al, 2009; Cloherty et al, 2010) around saccades.…”

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.…”

“…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. 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 (Forgacs et al 2008). In a study of voluntary saccades in both dark and light, parietal and occipital gamma power increased during the saccade and peaked prior to reaching new fixation.…”

“…This increase was expressed as gamma modulation index (GMI), which represents the ratio of intrasaccadic over presaccadic gamma. GMI has been suggested to be a part of the built-in pre-emptive neuronal computational (Forgacs et al 2008) framework which prepares the visual cortex to receive sensory information before the eyes reach their target.…”