State Dependent Neurophysiology: Depression
Introduction: The DSM-IV-TR proposes that patients suffering from MDD will display state-dependent irregularities during examination by electroencephalogram (EEG) and other experimental methods. This study sought to capture this state dependency by utilizing topographical EEG and connectivity and LORETA current source density in the alpha frequency domain would differ between groups as would pre-post task salivary cortisol levels.
Methods: This study was conducted with 23 (13 depressed) participants, 16 female, with a mean age of 20 ± 2.45. Depressed individuals had received a diagnosis of depression within the past year. We administered the SCID-R to depressed group. We collected salivary cortisol prior to any experimental conditions. Participants then provided 4 minute eyes-closed and eyes-opened baseline EEG recordings (ECB and EOB, respectively). The participants then completed the Beck Depression Inventory while EEG was continuously recorded. Items were presented for 8s in power point and responses were marked within the EEG record. These segments were extrapolated and compared for significance within and between groups. Post session cortisol was collected and analyzed. Although numerous differences may be expected, this study focuses on power, connectivity and LORETA current source density differences in the alpha frequency domain (8-12Hz) given its prominence in the depression literature.
Results: Minimal differences are seen between depressed and non-clinical groups for topographical absolute and relative power. Significant differences were found in asymmetry, coherence and phase measures between groups. Current source density in alpha differs between groups with depressed showing specific regional increases in right prefrontal regions. Notably, cortisol decreased relative to the BDI task in all subjects, with differences still evident between groups.
Discussion: As with many other studies, topographical power differences are sparse. Connectivity and LORETA current source density measures do reveal significant differences between groups and may provide a more accurate method for differential diagnosis of depressive disorder. Several studies have reported blunted cortisol responsivity in depression relative to stressors and our data appear to follow these results. Diagnostic, research, and clinical implications are discussed.