Graded changes in local functional connectivity of the brain in young people with depression

Major depressive disorder (MDD) is marked by significant changes to the coupling of spontaneous neural activity within various brain regions. However, many methods for assessing this local connectivity use fixed or arbitrary neighborhood sizes, resulting in a decreased capacity to capture smooth changes to the spatial gradient of local correlations. A newly developed method sensitive to classical anatomo-functional boundaries, Iso-Distant Average Correlation (IDAC), was therefore used to examine depression associated alterations to the local functional connectivity of the brain. One-hundred and forty-five adolescents and young adults with MDD and 95 healthy controls underwent a resting-state fMRI scan. Whole-brain functional connectivity maps of intracortical neural activity within iso-distant local areas (5-10mm, 15-20mm, and 25-30mm) were generated to characterize local fMRI signal similarities. Across all spatial distances, MDD participants demonstrated greater local functional connectivity of the bilateral posterior hippocampus, retrosplenial cortex, dorsal insula, fusiform gyrus, and supplementary motor area. Additionally, in the short and medium range connections there were depression associated alterations in the midcingulate (15-20mm and 25-30mm) and subgenual anterior cingulate (15-20mm). Our study identified increased synchrony of the neural activity in several regions commonly implicated in the neurobiology of depression; however, a subset of identified effects was dependent on the spatial distance under consideration. Longitudinal examination of these effects will clarify whether these differences are also found in other age groups and if this synchrony is additionally altered by continued disease progression. ### Competing Interest Statement The authors have declared no competing interest.