# Cross-sectional and longitudinal functional network alterations associated with subthreshold depressive symptoms in healthy older adults

## TL;DR

This study finds that even mild depressive symptoms in older adults are linked to changes in brain network connectivity, which could help detect and treat depression early.

## Contribution

The study identifies reduced connectivity in the ventral attention network as a potential early neural marker for depressive symptom progression in older adults.

## Key findings

- SDS are associated with decreased intra- and inter-network functional connectivity in older adults.
- Reduced connectivity within the ventral attention network at baseline predicts future increases in depressive symptoms.
- Right-hemispheric ventral attention network regions are particularly involved in these changes.

## Abstract

Subthreshold depressive symptoms (SDS) in older adults as a prodromal state of late-life depression (LLD) increase with age and are associated with elevated risk for cardio- and cerebrovascular diseases. LLD has been linked to functional brain network disruptions, including the ventral attention (VAN) and default mode network (DMN). Thus, identifying alterations in functional connectivity (FC) linked to SDS may be critical for the early detection and treatment of individuals at high-risk for LLD.

A total of 243 healthy older subjects (55–84 years; MAge = 67.0 ± 6.5) without a history of depression and current antidepressant intake from the 1000BRAINS sample with two timepoints of assessments were included in this study (time interval = 3.7 ± 0.7 years). SDS were measured using the Beck Depression Inventory II (BDI-II < 20) and linked to resting-state functional magnetic resonance imaging derived FC within and between seven large scale functional brain networks.

Both cross-sectional and longitudinal analyses revealed that SDS were associated with decreased intra- and inter-network FC. After Bonferroni correction for multiple comparisons, reduced FC within the VAN at baseline significantly predicted a longitudinal increase in depressive symptoms. This association was primarily driven by the somatic symptom domain of the BDI-II. Post-hoc analyses highlighted the particular involvement of right-hemispheric VAN regions.

Our findings support the hypothesis that even minimal to mild depressive symptoms in older adults are linked to disrupted functional network architecture. Specifically, reduced FC within the VAN may serve as an early neural marker for the emergence of depressive symptoms and vulnerability for the progression into clinically manifest LLD. Thus, offering potential for early detection and targeted intervention in subjects at high risk.