P123 Repeated measure stability of prefrontal transcranial direct current stimulation (tDCS) on functional MRI connectivity in healthy subjects

Abstract

Previous studies have shown that transcranial Direct Current Stimulation (tDCS) modulates functional brain connectivity. For example, increased connectivity within the Frontal Parietal Network (FPN) was found following anodal stimulation of the prefrontal cortex (PFC) (Keeser et al., 2011; Pena-Gomez et al., 2012), potentially reflecting a state of enhanced alertness. The aim of this study is two-folded: First, we want to investigate the stability of tDCS- and tACS-induced resting state network (RSN) modulations. Secondly, we are looking at additive effects of tACS on RSN modulations by comparing tACS stimulation preceded by sham tDCS to tACS stimulations preceded by active tDCS. We applied tDCS and tACS over the dorsolateral PFC (anode placed over F3, cathode over F4; intensity: 2 mA (tDCS), 25 Hz (tACS)) during concurrently acquired resting-state functional Magnetic Resonance Imaging (MRI). 20 male participants were tested according to a between-subject, double-blinded design. Each participant received 20 min of either real or sham tDCS and 10 min of tACS stimulation, each preceded and ensued by a resting state examination of 10 min. This procedure was conducted three times with at least seven days between each measurement to avoid carry-over effects. Within one participant, stimulation condition (real vs. sham tDCS) was held constant across all time points. The tACS stimulation was always an active stimulation. Based on whole-brain dual-regression analysis, preliminary results showed a significant effect for the comparison post tDCS > baseline across time points in two RSNs at an uncorrected p 20 voxels). For the Default Mode Network (DMN), an increased coactivation in the left superior frontal gyrus was observed for group 2. In the same group, increased coactivations were also identified for the right FPN in the left and right superior frontal gyrus. In group 1, no significant differences were found for the left FPN, but there was increased activation in the sub gyral for the DMN in this group. Group comparisons (post tDCS > baseline) across time points show increased activations within the left and right superior frontal gyrus for group 2. To test for test–retest reliability of tDCS, correlations between the tDCS effects of each time point can be calculated.