Mean response bias (<i>ß</i>) across the test and training blocks for the anodal (2 mA) and sham (0.1 mA) stimulation groups.

<p>Mean response bias (<i>ß</i>) across the test and training blocks for the anodal (2 mA) and sham (0.1 mA) stimulation groups.</p

Mean hit rate in the pre-training baseline, immediate post-training retention test, and 24-hour retention test blocks for the anodal (2 mA) and sham (0.1 mA) stimulation groups.

<p>Mean hit rate in the pre-training baseline, immediate post-training retention test, and 24-hour retention test blocks for the anodal (2 mA) and sham (0.1 mA) stimulation groups.</p

Mean false alarm rate in the pre-training baseline, immediate post-training retention test, and 24-hour retention test blocks for the anodal (2 mA) and sham (0.1 mA) stimulation groups.

<p>Mean false alarm rate in the pre-training baseline, immediate post-training retention test, and 24-hour retention test blocks for the anodal (2 mA) and sham (0.1 mA) stimulation groups.</p

Mean percentage of falsely identified threats on non-threat trials (false alarm rate) across the test and training blocks for the anodal (2 mA) and sham (0.1 mA) stimulation groups.

<p>Mean percentage of falsely identified threats on non-threat trials (false alarm rate) across the test and training blocks for the anodal (2 mA) and sham (0.1 mA) stimulation groups.</p

Examples of the concealed threat in images used for both test and training blocks.

<p>Similar scenarios could be repeated throughout the experiment but the presence of a threat varied from trial to trial. Top row, left image: an example of a concealed enemy combatant scenario, indicated by the barely visible tip of a firearm in the room at the top of the ladder. No threat is present in the right image. Bottom row, left image: example of a bomb that has been concealed by a stack of rocks. The bomb is indicated by a tiny object that is barely visible through the space between the rocks. No threat is present in the right image.</p

Mean sensation scores (on a 10-point scale, with 1 = no sensation and 10 = extreme sensation) for tingling, heat, and itching for the sham (0.1 mA) and anodal stimulation (2 mA) groups.

<p>Mean sensation scores (on a 10-point scale, with 1 = no sensation and 10 = extreme sensation) for tingling, heat, and itching for the sham (0.1 mA) and anodal stimulation (2 mA) groups.</p

Mean perceptual sensitivity (<i>d′</i>) in the pre-training baseline, immediate post-training retention test, and 24-hour retention test blocks for the anodal (2 mA) and sham (0.1 mA) stimulation groups.

<p>Mean perceptual sensitivity (<i>d′</i>) in the pre-training baseline, immediate post-training retention test, and 24-hour retention test blocks for the anodal (2 mA) and sham (0.1 mA) stimulation groups.</p

Individual differences in learning correlate with modulation of brain activity induced by transcranial direct current stimulation

<div><p>Transcranial direct current stimulation (tDCS) has been shown to enhance cognitive performance on a variety of tasks. It is hypothesized that tDCS enhances performance by affecting task related cortical excitability changes in networks underlying or connected to the site of stimulation facilitating long term potentiation. However, many recent studies have called into question the reliability and efficacy of tDCS to induce modulatory changes in brain activity. In this study, our goal is to investigate the individual differences in tDCS induced modulatory effects on brain activity related to the degree of enhancement in performance, providing insight into this lack of reliability. In accomplishing this goal, we used functional magnetic resonance imaging (fMRI) concurrently with tDCS stimulation (1 mA, 30 minutes duration) using a visual search task simulating real world conditions. The experiment consisted of three fMRI sessions: pre-training (no performance feedback), training (performance feedback which included response accuracy and target location and either real tDCS or sham stimulation given), and post-training (no performance feedback). The right posterior parietal cortex was selected as the site of anodal tDCS based on its known role in visual search and spatial attention processing. Our results identified a region in the right precentral gyrus, known to be involved with visual spatial attention and orienting, that showed tDCS induced task related changes in cortical excitability that were associated with individual differences in improved performance. This same region showed greater activity during the training session for target feedback of incorrect (target-error feedback) over correct trials for the tDCS stim over sham group indicating greater attention to target features during training feedback when trials were incorrect. These results give important insight into the nature of neural excitability induced by tDCS as it relates to variability in individual differences in improved performance shedding some light the apparent lack of reliability found in tDCS research.</p></div

Brain activity unique to the active stim group over the sham group for target feedback of incorrect trials relative to correct trials during the training session.

<p>A) Differential activity rendered on the surface of the cortex. A single cluster of activity is present in the pre- and post-central gyrus and the premotor cortex. The results are corrected for multiple comparisons at the cluster level (p < 0.05) using Monte-Carlo simulation (corrected cluster extent threshold greater than 757 contiguous voxels over uncorrected significance threshold of p < 0.005). Differential activity determined by region of interest analysis in the left (B) and Right (C) basal ganglia rendered on MRI anatomical slices. Significant at p < 0.05 using Monte-Carlo simulation (corrected cluster extent threshold = 38 contiguous voxels for left basal ganglia and 35 contiguous voxles for the right basal ganglia, over uncorrected significance threshold of p < 0.005 within the region of interest). To ensure that activity wasn’t related to differences in hit rate between the stim and sham group but rather processing differences between incorrect and correct trials we employed an exclusive mask of activity present for the hit rate weighted F contrast of incorrect—correct for stim over sham at a lenient threshold of p < 0.05 uncorrected.</p

Overlap in behavioral improvement related activity with target feedback activity that is greater for the active stim group over the sham group.

<p>Overlap in significant voxels for the two analyses (Improvement Related Activity and Target Feedback Activity) are rendered on the surface of the cortex and are present in the pre- and post-central gyrus.</p