Apathy Endorsement in Late Life Depression is Associated with Executive Dysfunction

Introduction

Executive function deficits are prevalent in late life depression (LLD) and linked to poorer outcomes. Little is known about the underlying factors that contribute to greater executive dysfunction in LLD, yet understanding these factors is critical for identifying new intervention targets to reduce the public health burden associated with depression and cognitive impairment in late life. Although negative affect has traditionally been the focus of scientific inquiry related to depressive symptomatology, emerging work is highlighting associations of Positive Valence System (PVS) dysfunction with depression. PVS functions are characterized by positive affect and approach behaviors toward potentially rewarding stimuli and are associated with better cognitive control in non-depressed adults. PVS deficits such as apathy are common in LLD and present as diminished goal-directed behavior, decreased interest in activities, and flattened affect. One prior study found that greater apathy was significantly associated with lower executive function performance in LLD, but more work is needed to characterize associations between PVS functions and executive dysfunction, including impairment rates. To this end, we examined associations between apathy endorsement in LLD and 1) performance on executive function measures and 2) rates of executive function impairment.

Methods

Baseline assessments of older adults with Major Depressive Disorder (N=228, Ages 65-91) were pooled across two studies: a longitudinal observational study (n=127) and a psychotherapy study (n=101). Participants completed measures of depression (15-item Geriatric Depression Scale [GDS], Hamilton Depression Rating Scale [HDRS]) and executive functions (EF; Trail Making Test B [TMTB], Stroop Color Word Interference [SCWI]) yielding raw scores and demographically corrected impairment ratings (i.e., performance at least 1 standard deviation below the normative mean). Apathy was defined as endorsement of having dropped many activities and interests (GDS, item 2). Differences in EF test performance by apathy status (present vs. absent) were first assessed by comparing raw scores (log-transformed for TMTB due to skewness) via independent samples t-tests (adjusted for unequal variances in performance scores between apathy groups). Linear regression analyses were additionally conducted to assess performance differences by apathy status after adjusting for demographic characteristics (age, gender, education) and concurrent depression severity (HDRS). Chi-square tests compared rates of demographically corrected EF impairment by apathy status and were followed up by logistic regression analyses to examine whether apathy status is associated with EF impairment differences after adjusting for concurrent depression severity.

Results

Apathy was endorsed by 67.5% of participants and was associated with significantly poorer performance on both TMTB (t=-3.39, p<.001) and SCWI (t=2.05, p=.042). Apathy endorsement remained significantly associated with poorer TMTB performance after controlling for demographic characteristics and concurrent depression severity (t=2.43, p=.016) but not SCWI (t=-1.25, p=.212). Apathy endorsement was also associated with demographically corrected impairment rates, with significant associations for TMTB (X^2=6.24, p=.012) and trend-level associations for SCWI (X^2=3.73, p = .054). These findings were retained after controlling for concurrent depression (TMTB: z=2.37, p=.018; SCWI: z=1.85, p=0.065).

Conclusions

Apathy endorsement is associated with executive dysfunction in LLD even after controlling for concurrent depression severity. Among the executive function measures examined, stronger effects were seen for cognitive set-shifting than for inhibition. Findings align with previous work and suggest that apathy in LLD may put these individuals at increased risk for executive dysfunction or that greater executive dysfunction puts individuals at risk for greater apathy. Longitudinal work is needed to determine the temporal course of these associations. The present study is limited by a single-item apathy measure and future work will benefit from including more comprehensive assessment of both apathy and executive functions to further evaluate possible links. With emerging research highlighting that better PVS functioning may be associated with improved cognitive outcomes during aging, it will be important to further characterize PVS functions in LLD. Future work may consider how interactive processes between PVS deficits and executive dysfunction may reinforce cognitive decline in LLD, as well as how intact PVS and cognitive control processes may protect against cognitive decline.