Distinct patterns of posterior default mode network‐medial temporal lobe connectivity in mild cognitive impairment and subjective cognitive decline

Abstract

AbstractBackgroundOlder adults with subjective cognitive decline (SCD) show alterations in functional connectivity of the posterior default mode network (DMN), but both increases and decreases have been reported, suggesting that changes in connectivity may be nonlinear across the AD spectrum. Alternatively, the variable findings may be attributable to heterogeneity within SCD samples. Specifically, studies of SCD exclude individuals with current depression, but history of past remitted depression is not typically ascertained. This is problematic because emerging evidence suggests that state‐independent aberrations in neural networks, including within posterior DMN, persist following recovery from depression. In the current study, we compared posterior DMN connectivity using resting state functional magnetic resonance imaging (rs‐fMRI) amongst SCD, mild cognitive impairment (MCI) or cognitively unimpaired (CU) older adults free of current or remitted depression.MethodParticipants were 58 older adults who were screened via psychiatric/medical assessment for current or past history of depression and neurological conditions, and consisted of 21 SCD [12F, mean age 70.6(SD5.5)] defined as perception of memory decline with concern or worry and normal neuropsychological (NP) test scores, 12 MCI [4F, mean age 73(SD6.8)] defined as subjective cognitive complaints with functional independence and impaired performance on >=2 NP tests, and 25 CU [15F, mean age 71.8(SD7.2)] based on normal NP scores and absence of subjective memory decline with worry. Rs‐fMRI was acquired using gradient‐echo EPI BOLD at 3T and processed using CONN toolbox. Seed analysis using a posterior cingulate cortex (PCC) seed (x=‐6, y=‐52, z=40) was performed. Hippocampus and parahippocampal gyrus were target regions‐of‐interest. Multivariate ANOVA was used to examine group differences in PCC connectivity followed by post hoc comparisons using Dunnett’s test.ResultGroups differed in PCC connectivity with the right hippocampus [F(2, 55)=3.74, P=.03] and left posterior parahippocampal gyrus [F(2, 55)=3.35, P=.042]. Relative to CU, PCC‐right hippocampal connectivity was reduced in MCI (P=.028), while PCC‐left parahippocampal connectivity was found in SCD (P=.024).ConclusionDisruptions in posterior DMN connectivity were observed in SCD and MCI that were not attributable to current or remitted depression. The distinct patterns of posterior DMN disruption are consistent with putative non‐linear changes in neural network connectivity with AD progression.