3 Results

3.1 Participant characteristics

Demographic and clinical characteristics of all participant groups are summarized in Table 1. The groups did not differ in age, sex and education. Healthy controls and patients showed significant differences in clinical scores. Comparing both patient groups, we found significant differences in medication status. Both patient groups did not differ in duration of illness and BDI-II- and BAI scores.

3.2 Resting state functional connectivity

Table 3 summarizes the network aberrations found for the three examined networks. Figure 1 illustrates the clusters found in their respective networks. Comparing MDD+AD and HC, MDD+AD showed a significantly reduced RSFC for the VAN with both the ECN and the DMN. No alteration in RSFC of the ECN and DMN could be found.
Between the DMN and the VAN, the right posterior cingulate cortex seed of the DMN showed a significantly decreased RSFC with regions in the VAN (RPCC to: right middle cingulate and paracingulate gyrus, t = 4.64, pcorr = .015; right middle cingulate and paracingulate gyrus, t = 5.86, pcorr = .011) and the left and right dorsal anterior insula of the VAN showed significantly decreased RSFC with regions in the DMN (RdaIns to: right anterior cingulate cortex, pregenual parts, t = 5.21,pcorr = < .001; LdaIns to: left anterior cingulate cortex, pregenual parts, t = 5.80,pcorr = <.001).
Between the ECN and the VAN, the left dorsomedial prefrontal cortex and the left dorsolateral prefrontal cortex of the ECN showed significantly decreased RSFC with the VAN (LdmPFC to: left middle cingulate and paracingulate gyri, t = 5.06, pcorr = .002; LdlPFC to: right middle cingulate and paracingulate gyri, t= 4.53, pcorr = .001). The left dorsal anterior insula of the VAN showed significantly reduced RSFC with the ECN (LdaIns to: right superior frontal gyrus, dorsolateral parts, t = 4.36,pcorr = .024).
The ECN showed significantly reduced RSFC on the within-network level (RdmPFC to: left middle frontal gyrus, t = 4.84,pcorr = .006).
We could not find any significant differences for the group comparisons including the MDD group (MDD – HC and MDD – MDD+AD).

3.3 Post-hoc regression analysis

Outcomes of regression analysis for the relationship of severity of symptoms as measured by BDI-II and BAI total scores and RSFC values of the found clusters within the patient group (MDD and MDD+AD) are shown in Table 3. No cluster showed a significant connection.
Furthermore, we did not find a significant effect of medication status on RSFC-values for the clusters that were found to be significant in group-wise analysis.