Structural integrity and functional connectivity of default mode network underlying the cognitive impairment in Late-onset depression

Abstract

Objective To determine the association between the functional changes and the structural lesions of the DMN underlying the cognitive impairments in Late-onset depression (LOD). Methods Thirty-two LOD patients and thirty-nine normal controls (NCs) were recruited and underwent resting-state fMRI and DTI scans. Cognition was evaluated with MMSE and a battery of neuropsychological measurements. Seed-based correlation analysis was performed to explore the functional connectivity (FC) of the DMN. Then deterministic tractography between FC-impaired regions were calculated to examine structural connectivity (SC). Tracts connecting FC-impaired regions were selected to count fiber number (FN) and to calculate average FA, AD and RD of all voxels along these fibers. Partial correlation analyses were applied to examine cognitive association of these altered FC and SC, controlling the effects of age and education. Results LOD patients showed decreased FC between PCC/Pcu and dACC as well as the thalamus. Decreased FA and increased RD of these fiber tracks connecting PCC/Pcu with dACC were found in LOD patients, without significant difference in AD and FN. The FC between PCC/Pcu and dACC was positively correlated with the FA of fiber tracks connecting them. The PCC/Pcu-dACC FC and the FA of the fiber tracks between them were both positively correlated with Symbol Digit Modalities Test and Verbal Fluency Test scores which conversely displayed negative association with RD. Conclusions The cognitive impairment in LOD, especially executive speed and semantic memory might be associated with the decreased FC in DMN which probably resulted from the demyelination of the white matter.