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Cortex. 2019 Apr;113:37-57. doi: 10.1016/j.cortex.2018.11.022. Epub 2018 Dec 7.

Impact of concurrent task performance on transcranial direct current stimulation (tDCS)-Induced changes in cortical physiology and working memory.

Author information

1
Monash Alfred Psychiatry Research Centre, The Alfred and Monash University, Central Clinical School, Victoria, Australia. Electronic address: aron.hill@monash.edu.
2
Brain and Mental Health Laboratory, School of Psychological Sciences and Monash Biomedical Imaging, Monash Institute of Cognitive and Clinical Neuroscience, Monash University, Australia.
3
Monash Alfred Psychiatry Research Centre, The Alfred and Monash University, Central Clinical School, Victoria, Australia; Epworth Healthcare, Camberwell, Victoria, Australia.
4
Monash Alfred Psychiatry Research Centre, The Alfred and Monash University, Central Clinical School, Victoria, Australia.

Abstract

Transcranial direct current stimulation (tDCS) provides a means of non-invasively inducing plasticity-related changes in neural circuits in vivo and is experiencing increasing use as a potential tool for modulating brain function. There is growing evidence that tDCS-related outcomes are likely to be influenced by an individual's brain state at the time of stimulation, i.e., effects show a degree of 'state-dependency'. However, few studies have examined the behavioural and physiological impact of state-dependency within cognitively salient brain regions. Here, we applied High-Definition tDCS (HD-tDCS) over the left dorsolateral prefrontal cortex (DLPFC) in 20 healthy participants, whilst they either remained at rest, or performed a cognitive task engaging working memory (WM). In a third condition sham stimulation was administered during task performance. Neurophysiological changes were probed using TMS-evoked potentials (TEPs), event-related potentials (ERPs) recorded during n-back WM tasks, and via resting-state EEG (RS-EEG). From a physiological perspective, our results indicate a degree of neuromodulation following HD-tDCS, regardless of task engagement, as evidenced by changes in TEP amplitudes following both active stimulation conditions. Changes in ERP (P3) amplitudes were also observed for the 2-Back task following stimulation delivered during task performance only. However, no changes were seen on RS-EEG for any condition, nor were any group-level effects of either stimulation condition observed on n-back performance. As such, these findings paint a complex picture of neural and behavioural responses to prefrontal stimulation in healthy subjects and provide only limited support for state-dependent effects of HD-tDCS over the DLPFC overall.

KEYWORDS:

Dorsolateral prefrontal cortex; TMS-EEG; Task-dependency; Transcranial direct current stimulation (tDCS); Working memory

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