Study design.

<p>After enrollment, participants attended six weekly sessions. A week prior to the training, baseline ADHD symptoms and cognitive functioning were assessed (<i>pre-test</i>). Then the four weekly training sessions commenced (60-min training time/session). A week after, the last training session, the behavioral post-assessment, was done (<i>post-test</i>). <i>ADHD = Attention Deficit Hyperactivity Disorder</i>, <i>fMRI = functional magnetic resonance imaging</i>, <i>NP-test = Neuropsychological tests</i>, <i>MSIT = Multi Source Interference task</i>, <i>SA-DOTS = Sustained Attention DOTS task</i>, <i>SART = Sustained Attention to Response Task</i>, <i>2-back WM = 2-back Working memory task</i>, <i>WAIS = Wechsler Adult Intelligence Scale</i>, <i>DS = Digit Span</i>, <i>LNS = Letter Number Sequencing</i>, <i>VC = Vocabulary</i>, <i>BD = Block Design</i>, <i>QCM = Questionnaire of Current Motivation</i>, <i>MCT = Mental Calculation Task</i>.</p

Pre-post behavioral assessment (within group).

<p>Pre-post behavioral assessment (within group).</p

Activation levels within dACC target regions during MRI training and transfer runs.

<p>The results demonstrate that all participants achieved the expected up-regulation of activation levels within the dACC target regions with training. Both groups showed a marked and significant increase in dACC activation level from the third session onwards, which was evident during <i>training runs</i> (panel A, marked with an asterisk), and marginally significant during <i>transfer runs</i> (panel B). Importantly, participants were able to sustain increased activation levels until the end of training. There were no significant group differences and neither group demonstrated ability to differently up-regulate the dACC activation levels during the <i>medium</i> and <i>high difficulty</i> condition.</p

Activation levels within dACC target regions during localization tasks.

<p>Participants across groups showed significantly increased activation levels in the dACC target region during the <i>interference</i> condition of the MSIT (panel A, marked with an asterisk), and the <i>mental calculation</i> condition of the MCT (panel B). There were no changes in performance over time, confirming that both groups consistently performed the task as instructed.</p

CONSORT Flow Diagram.

<p>Eighteen participants volunteered and were screened, thirteen participants were included in the study and randomly assigned to a group.</p

Localization of dACC target regions.

<p>Activation during the localization tasks is depicted for the interference task (MSIT, panel A, peak activation x = 8, y = 10, z = 45, Talairach space) and the mental calculation task (MCT, panel B, peak activation x = -8, y = 10, z = 48, Talairach space). To verify if the targeted dACC region was localized/defined within the online procedure, a whole-brain random effects GLM analysis (p<0.05, corrected at cluster level) was performed for the contrast <i>interference</i> vs. <i>no interference</i> (MSIT, panel A), and the contrast <i>mental calculation</i> vs. <i>mental singing</i> (MCT, panel B). Panel C depicts the location of the online defined individual dACC target regions around their average location (x = 2, y = 15, z = 39, Talairach space, neurofeedback group = blue tints, control group = green tints). The slightly more anterior location of the dACC target regions respective to the peak of activation may have resulted from a preference for the most anterior clusters during the localization procedure, which have been shown to be hypo-activated in ADHD patients [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0170795#pone.0170795.ref026" target="_blank">26</a>].</p

Grand average stimulus-locked waveforms for the P3a at FCz and the P3b at Pz for each group separately.

<p>Grand average stimulus-locked waveforms for the P3a at FCz and the P3b at Pz for each group separately.</p

Behavioural results for the psychopathic, non-psychopathic and the control group.

<p>Group means are reported with their standard deviation between brackets. Reaction times are reported in msec and accuracy measures in counts. Significant group differences are flagged.</p

Group characteristics for the psychopathic, non-psychopathic and the control group.

<p>Group means are reported with their standard deviation between brackets. Significant Group differences are flagged.</p

Average peak amplitudes for novels and targets at FCz and Pz for the psychopathic, non-psychopathic and control group, respectively.

<p>Average peak amplitudes for novels and targets at FCz and Pz for the psychopathic, non-psychopathic and control group, respectively.</p