Despite its widespread use in cognitive studies, there is still limited understanding of whether and how transcranial direct current stimulation (tDCS) modulates brain network function. To clarify its physiological effects, we assessed brain network function using functional magnetic resonance imaging (fMRI) simultaneously acquired during tDCS stimulation. Cognitive state was manipulated by having subjects perform a Choice Reaction Task or being at “rest.” A novel factorial design was used to assess the effects of brain state and polarity. Anodal and cathodal tDCS were applied to the right inferior frontal gyrus (rIFG), a region involved in controlling activity large-scale intrinsic connectivity networks during switches of cognitive state. tDCS produced widespread modulation of brain activity in a polarity and brain state dependent manner. In the absence of task, the main effect of tDCS was to accentuate default mode network (DMN) activation and salience network (SN) deactivation. In contrast, during task performance, tDCS increased SN activation. In the absence of task, the main effect of anodal tDCS was more pronounced, whereas cathodal tDCS had a greater effect during task performance. Cathodal tDCS also accentuated the within-DMN connectivity associated with task performance. There were minimal main effects of stimulation on network connectivity. These results demonstrate that rIFG tDCS can modulate the activity and functional connectivity of large-scale brain networks involved in cognitive function, in a brain state and polarity dependent manner. This study provides an important insight into mechanisms by which tDCS may modulate cognitive function, and also has implications for the design of future stimulation studies.
Bibliographical noteFunding Information:
NIH Clinical Center, Grant/Award Number: MH110217MH111439; Programme Grants for Applied Research, Grant/Award Number: NIHR-RP-011-048; Wellcome Trust, Grant/ Award Number: 103045/Z/13/Z103429/ Z/13/Z; NIHR Imperial College London Biomedical Research Centre; National Institute for Health Research (NIHR) Professorship; NIH, Grant/Award Number: 103429/Z/13/Z; NIHR Imperial BRC, Grant/Award Number: NIHR-RP-011-048; Sir Henry Wellcome Trust Fellowship, Grant/Award Number: 103045/ Z/13/Z; Wellcome Trust Clinical Research Training Fellowship
LML is supported by a Wellcome Trust Clinical Research Training Fellowship (103429/Z/13/Z). IV is supported by a Sir Henry Wellcome Trust Fellowship (103045/Z/13/Z) and receives funding from the NIHR Imperial BRC. AO is supported in parts by NIH grants MH110217 and MH111439. DJS is supported by a National Institute for Health Research (NIHR) Professorship (NIHR-RP-011-048). We would like to thank Dr Jonathan Howard for tireless and insightful technical and methodological assistance. This study was conducted at the Imperial College Clinical Imaging Facility. The study was supported by the NIHR Imperial College London Biomedical Research Centre.
- default mode network
- magnetic resonance imaging
- salience network