Abstract
Visual working memory (VWM) refers to people’s ability to maintain and manipulate visual information on line. Its capacity varies between individuals, and neuroimaging studies have suggested a link between one’s VWM capacity and theta power in the parietal cortex. However, it is unclear how the parietal cortices communicate with each other in order to support VWM processing. In two experiments we employed transcranial alternate current stimulation (tACS) to use frequency-specific (6 Hz) alternating current to modulate theta oscillation between the left and right parietal cortex with either in-phase (0° difference, Exp 1), anti-phase (180° difference, Exp 2), or sham sinusoidal current stimulation. In Experiment 1, in-phase theta tACS induced an improved VWM performance, but only in low-performers, whereas high-performers suffered a marginally-significant VWM impairment. In Experiment 2, anti-phase theta tACS did not help the low-performers, but significantly impaired high-performers’ VWM capacity. These results not only provide causal evidence for theta oscillation in VWM processing, they also highlight the intricate interaction between tACS and individual differences—where the same protocol that enhances low-performers’ VWM can backfire for the high-performers. We propose that signal complexity via coherent timing and phase synchronization within the bilateral parietal network is crucial for successful VWM functioning.
Highlights
Visual working memory (VWM) refers to the complex interaction between visual attention and short-term memory, and is essential for maintaining a stable perception of the world by preserving information across blinks and saccades[1]
In two studies[14,16], they reported that only participants below average were able to benefit from anodal transcranial direct current stimulation (tDCS) over the right posterior parietal cortex (PPC), with relevant EEG markers that corresponded with the behavioral data
Participants were sorted based on their natural VWM performance in the sham condition to see whether there was any interaction between individual differences and brain stimulation[17]
Summary
Visual working memory (VWM) refers to the complex interaction between visual attention and short-term memory, and is essential for maintaining a stable perception of the world by preserving information across blinks and saccades[1]. Current to induce excitatory or inhibitory reactions from the brain, researchers have found that anodal tDCS over the right PPC can effectively boost people’s VWM capacity and performance[14,15]. This boost, did not work for everyone. The high-performers did not show an improvement or impairment after stimulation Together, these studies suggest that signals of certain frequency bands can be indicative of people’s VWM performance, and that brain stimulation can be a useful approach in inducing such oscillation to establish causal evidence and neural entrainment, as long as the interactive effect between brain stimulation and intrinsic individual differences (e.g., low- vs high-performers)[17] is taken into account. Using a change detection task, Darriba et al.[22] observed higher theta power over the parietal-occipital sites when a change was consciously detected
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