*4.1. Overview of ECN*

The ECN, a functionally linked system, consists of brain structure cores that include the dorsolateral prefrontal cortex (dlPFC), medial frontal cortex, lateral parietal cortex, cerebellum, and supplementary motor area [176]. Initially, studies investigating executive function using task-based fMRI identified the coactivation patterns of an ECN during executive function tasks [177]. Beyond task-based fMRI, rs-fMRI studies, and structural MRI studies have also identified an ECN [176,178]. Moreover, a close correlation between executive function changes with aging and alterations in the ECN have been reported [179]. This correlation has been reported in studies that used the ECN to study the functional mechanisms of executive function changes in patients with psychiatric disorders, Parkinson's disease [180], MCI [181], AD [182], and LLD [183].

#### *4.2. rs-fMRI Studies Associated with ECN in LLD*

Disruption of the ECN in LLD patients with current depression symptoms has been consistently reported compared to healthy controls [184,185]. Particularly, seed-based analyses using the dlPFC as the seed region demonstrated decreased FC in the frontoparietal areas in LLD individuals with current depression [41]. Other studies using the cerebellum as a seed region reported decreased FC in ECN nodes, including in dlPFC and the parietal cortex, as well as DMN nodes [186,187]. Studies using ICA analysis presented different connectivity patterns for each region in the ECN, with increased FC in the inferior parietal but decreased FC in the dlPFC and superior frontal areas [39]. This decreased connectivity associated with the ECN has been consistently presented in other rs-fMRI studies using ReHo [94,188] and ALFF [40]. Additionally, LLD remitters also demonstrated decreased FC in the frontal-parietal cortex 3 months after remission [189]. After 21 months, individuals with remitted LLD presented a return to decreased FC.

Executive dysfunction is a common symptom in LLD patients. About 30 to 40% of nondemented elders with LLD demonstrate executive dysfunction during neuropsychological tests [190]. Disruption of the ECN was associated with executive dysfunction that included susceptibility to distraction, an inability to sustain attention, poor multitasking, organizational difficulties, and concrete or rigid thinking [191]. A recent study reported that LLD patients' FC between the dlPFC and other bilateral regions was negatively associated with executive function in LLD subjects [192]. Researchers reported that executive

dysfunction is associated with greater functional disability levels in LLD [193,194]. Deficits in word-list generation and response inhibition that represent executive function predict poor and slow antidepressant responses and relapses [195,196]. In this regard, the ECN seems to be related to the LLD's clinical prognosis associated with executive dysfunction. We presented key findings associated with LLD in Table 3 and characteristics of main rs-fMRI studies in Supplementary Table S4.

**Table 3.** Summary of key findings of rs-fMRI studies associated with the executive control network (ECN) in late-life depression (LLD) patients included in the review.


Abbreviations: ECN, executive control network.
