sLORETA and fMRI Detection of Medial Prefrontal Default Network Anomalies in Adult ADHD

Abstract

Attention deficit hyperactivity disorder (ADHD) is a developmental psychiatric disorder thought to affect approximately 5 to 10% of school-age children, of whom 30 to 65% continue to exhibit symptoms into adulthood. The prevalence of ADHD in adults is also an estimated 4%, second only to depression. Across studies there appear to be significant network dysfunctions involved in ADHD. Typically the foci of interest in ADHD included the insular cortices, frontal lobes, basal ganglia, and cerebellum. More recently, attention has been directed to the default network of the brain and its functional integrity in ADHD with focus on the precuneus and parietal lobes and interactions with medial prefrontal cortices. Functional magnetic resonance imaging (fMRI) measures neurovascular coupling as measured by the blood oxygenated level dependent signal (BOLD). Electroencephalogram (EEG) measures brain electrical information. Because fMRI is an indirect measure of neuronal activity and EEG is a direct measure, combining the results from these two imaging modalities under the same task conditions may provide a more complete story as to the what (EEG) and where (fMRI) activity exists. This article discusses the benefits of using standardized low resolution electromagnetic tomography (sLORETA) analysis of the EEG as compared to fMRI. The goal of the study, the data from which we use for our justification, was to discover the functional differences in ADHD and non-ADHD brains with different brain imaging modalities. We hoped to elucidate functional connectivity patterns by interpreting the data acquired with the EEG using sLORETA and the data acquired with the fMRI scans. We further hoped to find correlation with the sLORETA and fMRI interpretations so as to confirm that EEG is an adequate stand-alone methodology to evaluate ADHD. Participants included 6 ADHD and 7 non-ADHD subjects. They were initially interviewed by phone and administered the Connors Rating Scale and the Mini International Neuropsychiatric Interview to determine accuracy of symptom reporting and to rule out psychological comorbidities. Exclusion criteria consisted of previous head trauma, recent drug or alcohol abuse (14 days), or neurological syndromes. We recorded sequential 19-channel EEG and fMRI during the eyes-open and eyes-closed states and while performing the Stroop test. The QEEG results were evaluated with comparison to a normative database and with sLORETA analysis. Functional connectivity was assessed using the seed-based approach in sLORETA. The fMRI results were evaluated using Brain Voyager™ and other neuroimaging software packages. sLORETA and fMRI data identify a region in medial Brodmann Area (BA) 10 of the default network. Furthermore, regional frontal differences extend to medial BA 32 with more emphasis to left prefrontal. sLORETA determines there is less current source density at BA 10 in the ADHD participants than controls. sLORETA is adequate in localizing the sources of the EEG in the default network as contrasted with fMRI. It is important to note that sLORETA can provide important information about the direction of difference relative to the BOLD signal increase, which cannot be done with the fMRI alone.

Acknowledgments

This study was partially funded by the ISNR Research Foundation, the Hubbard Foundation, Mitsar, Ltd and NovaTech EEG. We thank Dr. David Hubbard of the Hubbard Foundation for the use of the fMRI scanner at no cost, Dr. Leslie Sherlin of NovaTech EEG and Mitsar International for the loan of the Mitsar 202 and WinEEG training, and the ISNR Research Foundation for providing funds for organizational and technical aspects of this study.