Abstract
Orienting spatial attention has been associated with interhemispheric asymmetry of power in the α- and γ-band. Specifically, increased α-power has been linked to the inhibition of unattended sensory streams (e.g. the unattended visual field), while increased γ-power is associated with active sensory processing. Here, we aimed to differentially modulate endogenous and exogenous visual-spatial attention using transcranial alternating current stimulation (tACS). In a single-blind, within-subject design, participants performed several blocks of a spatial cueing task comprised of endogenous and exogenous cues while receiving lateralized α- or γ-tACS or no stimulation over left or right occipital-parietal areas. We found a significant, differential effect of α- and γ-tACS on endogenous (top-down) spatial attention but not on exogenous (bottom-up) attention. The effect was specific to tACS applied to the left hemisphere and driven by a modulation of attentional disengagement and re-orientation as measured during invalid trials. Our results indicate a causal role of α-/γ-oscillations for top-down (endogenous) attention. They may further suggest a left hemispheric dominance in controlling interhemispheric α-/γ-power asymmetry. The absence of an effect on exogenous attention may be indicative of a differential role of α-/γ-oscillations during different attention types or spatially distinct attentional subsystems.
Highlights
At any given moment, our sensory systems are confronted with an overwhelming amount of information
We hypothesized that during α-transcranial alternating current stimulation (tACS) applied to the occipital cortex contralateral to the cued direction, reaction times (RTs) increase after valid cues, while RTs decrease after invalid cues, as compared to RTs after these cues in absence of tACS and during γ-tACS
The current study investigated whether lateralized α- and γ-tACS, aiming to modulate interhemispheric α-/γpower asymmetry over occipital and posterior-parietal cortices, modulates visual-spatial attention
Summary
Our sensory systems are confronted with an overwhelming amount of information. Α-oscillations are hypothesized to reflect inhibition of task irrelevant cortical a reas[12,13], while γ-oscillations are thought to reflect active information p rocessing[12] In line with this idea, increased power in the α-frequency band is commonly observed over cortical areas that process inputs from the unattended hemifield[3,4,5,6,7,10,11], while increased γ-oscillations have been observed over regions responsible for processing the attended locations[8,10,11]. We aimed to extent this finding to the visual domain as well as to exogenous attention To this end, we aimed to increase or decrease interhemispheric α- and γ-power asymmetry by applying lateralized tACS at α- or γ-frequency over the left or right occipital cortex while participants performed a visual-spatial cueing paradigm comprised of endogenous and exogenous cues.
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