Aim:  Reports on resting brain activity in healthy controls have described a default‐mode network (DMN) and important differences in DMN connectivity have emerged for several psychiatric conditions. No study to date, however, has investigated resting‐state DMN in relatively early depression before years of medication treatment. The objective of the present study was, therefore, to investigate the DMN in patients seeking help from specialized mental health services for the first time for symptoms of depression.Methods:  Fourteen depressed subjects and 15 matched controls were scanned using 4‐T functional magnetic resonance imaging while resting with eyes closed. All but one subject was medication free. A precuneus/posterior cingulate cortex (P/PCC) seed‐region connectivity analysis was used to identify the DMN and compare study groups in regions of relevance to depression.Results:  The P/PCC analysis identified the DMN well in both study groups, consistent with prior literature. Direct comparison showed significantly reduced correlation between the P/PCC and the bilateral caudate in depression compared with controls and no areas of increased connectivity in the depressed group.Conclusions:  The present study is the first to investigate resting‐state DMN in the early stages of treatment‐seeking for depression. Depressed subjects had decreased connectivity between the P/PCC and the bilateral caudate, regions known to be involved in motivation and reward processing. Deficits in DMN connectivity with the caudate may be an early manifestation of major depressive disorder.

Reward-processing neurocircuitry has been delineated using verbal or visual processing and/or decision-making tasks. We examined more basic processes of listening to enjoyable music in healthy and depressed patients. The paradigm was passive, individualized, and brief. Sixteen depressed and 15 control individuals provided favorite music and identified neutral music from selections provided. In the fMRI scanner, individuals heard their neutral and their favorite music for 3 min each. Favorite versus neutral music-listening contrasts showed greater activation in controls than depressed patients in medial orbital frontal cortex and nucleus accumbens/ventral striatum. Left medial prefrontal cortex activity was positively correlated with pleasure scores, whereas middle temporal cortex and globus pallidus were negatively correlated with pleasure. This paradigm activated neurocircuitry of reward processing and showed clinically meaningful alterations in depression.

Discriminating between bipolar disorder (BD) and major depressive disorder (MDD) is a major clinical challenge due to the absence of known biomarkers; hence a better understanding of their pathophysiology and brain alterations is urgently needed. Given the complexity, feature selection is especially important in neuroimaging applications, however, feature dimension and model understanding present serious challenges. In this study, a novel feature selection approach based on linear support vector machine with a forward-backward search strategy (SVM-FoBa) was developed and applied to structural and resting-state functional magnetic resonance imaging data collected from 21 BD, 25 MDD and 23 healthy controls. Discriminative features were drawn from both data modalities, with which the classification of BD and MDD achieved an accuracy of 92.1% (1000 bootstrap resamples). Weight analysis of the selected features further revealed that the inferior frontal gyrus may characterize a central role in BD-MDD differentiation, in addition to the default mode network and the cerebellum. A modality-wise comparison also suggested that functional information outweighs anatomical by a large margin when classifying the two clinical disorders. This work validated the advantages of multimodal joint analysis and the effectiveness of SVM-FoBa, which has potential for use in identifying possible biomarkers for several mental disorders.