Parietal alpha tACS shows inconsistent effects on visuospatial attention.

Andra Coldea,Gregor Thut,Stephanie Morand,Domenica Veniero,Monika Harvey,Andrea Antal

doi:10.1371/journal.pone.0255424

Abstract

Transcranial alternating current stimulation (tACS) is a popular technique that has been used for manipulating brain oscillations and inferring causality regarding the brain-behaviour relationship. Although it is a promising tool, the variability of tACS results has raised questions regarding the robustness and reproducibility of its effects. Building on recent research using tACS to modulate visuospatial attention, we here attempted to replicate findings of lateralized parietal tACS at alpha frequency to induce a change in attention bias away from the contra- towards the ipsilateral visual hemifield. 40 healthy participants underwent tACS in two separate sessions where either 10 Hz tACS or sham was applied via a high-density montage over the left parietal cortex at 1.5 mA for 20 min, while performance was assessed in an endogenous attention task. Task and tACS parameters were chosen to match those of previous studies reporting positive effects. Unlike these studies, we did not observe lateralized parietal alpha tACS to affect attention deployment or visual processing across the hemifields as compared to sham. Likewise, additional resting electroencephalography immediately offline to tACS did not reveal any notable effects on individual alpha power or frequency. Our study emphasizes the need for more replication studies and systematic investigations of the factors that drive tACS effects.

Highlights

While the neural correlates of cognitive processes can be identified using brain imaging techniques, it is possible to obtain causal evidence on brain-behaviour relationships with the use of non-invasive brain stimulation methods
Several recent studies using alpha Transcranial alternating current stimulation (tACS) have reported consistent effects on behavioural measures of spatial attention in both the visual and auditory modalities during tACS [36,37,38,39,40]. We tested this effect using the same endogenous attention task, stimulation site and high-density tACS setup as Schuhmann and colleagues [36], as well as a tACS intensity and duration of similar magnitude than other groups reporting effects [37,38,39,40]. Based on this prior literature, we expected that 10 Hz tACS applied over the left posterior parietal cortex should induce a shift in bias away from the right and towards the left hemispace
Taking into account the evidence coming from EEG [18, 20, 23, 25] and the tACS literature [36,37,38,39,40] supporting a role of alpha oscillations in visuospatial attention, our results are unexpected

Summary

Introduction

While the neural correlates of cognitive processes can be identified using brain imaging techniques, it is possible to obtain causal evidence on brain-behaviour relationships with the use of non-invasive (transcranial) brain stimulation methods. Transcranial alternating current stimulation (tACS), in particular, is of interest for probing causality between oscillatory activity of the brain and behaviour, as the sinusoidal tACS-currents hold promise to interact with intrinsic brain oscillations in a frequency-specific manner [1,2,3,4]. TACS has been gaining popularity in the last decade [3, 5], yet many controversies remain unresolved (see [6] for a review). It has been assumed that tACS-effects are caused by entrainment of brain oscillations and/or neuroplasticity [7,8,9].

Methods

Results

Conclusion