Effects of prefrontal bipolar and high-definition transcranial direct current stimulation on cortical reactivity and working memory in healthy adults

• Published in: NeuroImage (Orlando, Fla.) Vol. 152; pp. 142 - 157
• Main Authors: Hill, Aron T., Rogasch, Nigel C., Fitzgerald, Paul B., Hoy, Kate E.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15.05.2017; Elsevier Limited
• Subjects: Adult; Adults; Bipolar disorder; Brain; Brain research; Cerebral Cortex - physiology; Cognition & reasoning; Cognitive ability; Cortex; Direct current; Dorsolateral prefrontal cortex; EEG; Electrical stimulation of the brain; Electrodes; Electroencephalography; ESB; Evoked potentials; Excitability; Female; HD-tDCS; Humans; Magnetic fields; Male; Memory; Memory, Short-Term - physiology; Motor task performance; Neurobiology; Neuromodulation; Oscillations; Short term memory; Stimulation; tDCS; TMS-EEG; Transcranial Direct Current Stimulation - methods; Transcranial magnetic stimulation; Working memory; Young Adult; Dorsolateral prefrontal cortex; TMS-EEG; HD-tDCS; Working memory; tDCS
• ISSN: 1053-8119; 1095-9572
• DOI: 10.1016/j.neuroimage.2017.03.001

Transcranial direct current stimulation (tDCS) is a well-recognised neuromodulatory technology which has been shown to induce short-lasting changes in motor-cortical excitability. The recent and rapid expansion of tDCS into the cognitive domain, however, necessitates deeper mechanistic understanding of its neurophysiological effects over non-motor brain regions. The present study utilised transcranial magnetic stimulation combined with electroencephalography (TMS-EEG) to probe the immediate and longer-term effects of both a bipolar (BP-tDCS) and more focal 4×1 High-Definition tDCS (HD-tDCS) montage applied over the left DLPFC on TMS-evoked potentials (TEPs) and oscillations in 19 healthy adult participants. 2-back working memory (WM) performance was also assessed as a marker of cognitive function. Region of interest (ROI) analyses taken from the F1 electrode directly adjacent to the stimulation site revealed increased P60 TEP amplitudes at this location 5min following BP-tDCS and 30min following HD-tDCS. Further global cluster based analyses of all scalp electrodes revealed widespread neuromodulatory changes following HD-tDCS, but not BP-tDCS, both five and 30min after stimulation, with reductions also detected in both beta and gamma oscillatory power over parieto-occipital channels 30min after stimulation. No significant changes in WM performance were observed following either HD-tDCS or BP-tDCS. This study highlights the capacity for single-session prefrontal anodal tDCS montages to modulate neurophysiological processes, as assessed with TMS-EEG. •HD-tDCS and BP-tDCS applied over the DLPFC.•Neurophysiological effects examined with TMS-EEG.•Working memory performance examined with 2-back task.•HD-tDCS produced robust and widespread changes in cortical reactivity.•No significant changes in working memory performance were observed.