Abstract
This study uses simultaneous transcranial direct current stimulation (tDCS) and functional MRI (fMRI) to investigate tDCS modulation of resting state activity and connectivity that underlies enhancement in behavioral performance. The experiment consisted of three sessions within the fMRI scanner in which participants conducted a visual search task: Session 1: Pre-training (no performance feedback), Session 2: Training (performance feedback given), Session 3: Post-training (no performance feedback). Resting state activity was recorded during the last 5 min of each session. During the 2nd session one group of participants underwent 1 mA tDCS stimulation and another underwent sham stimulation over the right posterior parietal cortex. Resting state spontaneous activity, as measured by fractional amplitude of low frequency fluctuations (fALFF), for session 2 showed significant differences between the tDCS stim and sham groups in the precuneus. Resting state functional connectivity from the precuneus to the substantia nigra, a subcortical dopaminergic region, was found to correlate with future improvement in visual search task performance for the stim over the sham group during active stimulation in session 2. The after-effect of stimulation on resting state functional connectivity was measured following a post-training experimental session (session 3). The left cerebellum Lobule VIIa Crus I showed performance related enhancement in resting state functional connectivity for the tDCS stim over the sham group. The ability to determine the relationship that the relative strength of resting state functional connectivity for an individual undergoing tDCS has on future enhancement in behavioral performance has wide ranging implications for neuroergonomic as well as therapeutic, and rehabilitative applications.
Highlights
In recent years there has been an explosion of research investigating a method by which to augment human cognition by passing a low amplitude direct current through a person’s head and enhancing human performance and abilities (Coffman et al, 2014)
While one may expect these effects to be localized on the cortex near the stimulating electrode, functional MRI studies have shown modulation in activity in distal brain regions suggesting possible network effects induced by transcranial direct current stimulation (tDCS) (Clemens et al, 2014; Ellison et al, 2014; Weber et al, 2014)
The behavioral results in terms of percent correct on the visual search task for the tDCS stim and sham groups are as follows: there was a significant enhancement in performance post- relative to pre-training (ANOVA F(2,52) = 12.47, p < 0.05)
Summary
In recent years there has been an explosion of research investigating a method by which to augment human cognition by passing a low amplitude direct current (typically in the range of 0.5–2 mA) through a person’s head and enhancing human performance and abilities (Coffman et al, 2014). While one may expect these effects to be localized on the cortex near the stimulating electrode, functional MRI (fMRI) studies have shown modulation in activity in distal brain regions suggesting possible network effects induced by tDCS (Clemens et al, 2014; Ellison et al, 2014; Weber et al, 2014). It is our goal in this study to use simultaneous tDCS and fMRI to investigate the relationship between modulation in resting state activity as well as resting state functional connectivity of the brain correlated with improved performance as a result of stimulation. Previous studies using tDCS and fMRI have revealed, that as a result of stimulation, resting state networks can show wide spread changes in activity and connectivity in cortical and subcortical brain regions (Saiote et al, 2013; Clemens et al, 2014)
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