Abstract
In a previous study using transcranial alternating current stimulation (tACS), we found preliminary evidence that phase coherence in the alpha band (8–12 Hz) within the fronto-parietal network may critically support top-down control of spatial attention (van Schouwenburg et al., 2017). Specifically, synchronous alpha-band stimulation over the right frontal and parietal cortex (0° relative phase) was associated with changes in performance and fronto-parietal coherence during a spatial attention task as compared to sham stimulation. In the current study, we firstly aimed to replicate these findings with synchronous tACS. Second, we extended our previous protocol by adding a second tACS condition in which the right frontal and parietal cortex were stimulated in a desynchronous fashion (180° relative phase), to test the specificity of the changes observed in our previous study. Participants (n = 23) were tested in three different sessions in which they received either synchronous, desynchronous, or sham stimulation over the right frontal and parietal cortex. In contrast to our previous study, we found no spatially selective effects of stimulation on behavior or coherence in either stimulation protocol compared to sham. We highlight some of the differences in study design that may have contributed to this discrepancy in findings and more generally may determine the effectiveness of tACS.
Highlights
In daily life, our brain is constantly bombarded with more sensory information than it can fully process
We found that a group of participants that received sham stimulation showed a spatial bias both in terms of behavior and fronto-parietal connectivity
In line with many other studies, participants were faster in valid trials, followed by neutral trials, and invalid trials. (Results from post hoc pairwise comparisons: valid vs. neutral, p < 0.001; valid vs. invalid, p < 0.001; neutral vs. invalid, p = 0.001.) In our previous study, we found that participants who received sham stimulation were faster for targets in the right hemifield, while participants who received synchronous stimulation showed no spatial attention bias
Summary
Our brain is constantly bombarded with more sensory information than it can fully process This necessitates the selection of sensory information based on goal-relevance, a process subserved by top–down attention. Spatial attention paradigms are widely used to study the neural underpinnings of top–down attention In these tasks, participants receive a cue that indicates the most likely location of an upcoming target. It has been replicated many times that participants respond faster and more accurately to cued (i.e., attended) targets compared to uncued (i.e., unattended) targets. This benefit has been attributed to the fact that participants can direct their focus of attention in advance to the relevant location (Posner, 1980)
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