Pilot Data Assessing the Functional Integrity of the Default Network in Adult ADHD with fMRI and sLORETA

Resumen

Intrinsic functional connectivity within the default mode network (DMN) of the brain has gained growing interest in attention deficit/hyperactivity disorder (ADHD). The DMN is proposed to support such core functions as theory of mind, self-related activities such as autobiographical self, stimulus independent thought, self-projection, self-reference, and
introspective processes as well as central features of self-regulation, task compliance, and executive functions. Based on prior data showing that sLORETA and fMRI localize DMN regions with complementary accuracy, we hypothesized that this combination of methods could provide important information about the functional integrity of DMN connectivity with special attention between parietal and medial prefrontal regions. This study was conducted with 6 adults with ADHD and 7 age-similar, nonclinical controls. The present study recorded brain activity using both EEG and fMRI during rest and a Stroop paradigm. For this study only the eyes-opened rest data were analyzed using the sLORETA and fMRI psychophysiological interaction model respectively. sLORETA functional connectivity differences were assessed with Pearson’s correlation measures and Fisher’s Z test to examine the strength of the obtained coefficients between groups within the DMN. Differences in functional integrity of the DMN were found for most frequencies except theta, which did not show any difference between groups. Of interest, the ADHD group showed greater intrinsic functional connectivity in the alpha frequency range between medial prefrontal and left parietal regions. Functional connectivity within the DMN in both groups was comparable between both imaging modalities, with sLORETA providing evidence of the frequency-specific meaning of the  associations. This study furthers the requisite for utilizing sLORETA in combination with fMRI to obtain knowledge of the connectivity in the context of EEG frequency-specific parameters. The study data offer preliminary evidence demonstrating the importance of left parieto-occipital regions to ADHD and potential neural resources that may be compromised in ADHD that are specifically involved in self-regulation, working memory, and executive functions.