White-matter tract integrity in late-life depression: associations with severity and cognition

Depression in Alzheimer's Disease: Epidemiology, Mechanisms, and Treatment

Depression and Alzheimer's disease (AD) are substantial public health concerns. In the past decades, a link between the 2 disease entities has received extensive acknowledgment, yet the complex nature of this relationship demands further clarification. Some evidence indicates that midlife depression may be an AD risk factor, while a chronic course of depression in late life may be a precursor to or symptom of dementia. Recently, multiple pathophysiological mechanisms have been proposed to underlie the bidirectional relationship between depression and AD, including genetic predisposition, immune dysregulation, accumulation of AD-related biomarkers (e.g., amyloid-β and tau), and alterations in brain structure. Accordingly, numerous therapeutic approaches, such as pharmacology treatments, psychotherapy, and lifestyle interventions, have been suggested as potential means of interfering with these pathways. However, the current literature on this topic remains fragmented and lacks a comprehensive review characterizing the association between depression and AD. In this review, we aim to address these gaps by providing an overview of the co-occurrence and temporal relationship between depression and AD, as well as exploring their underlying mechanisms. We also examine the current therapeutic regimens for depression and their implications for AD management and outline key challenges facing the field.

Association of white matter hyperintensities and clinical vascular burden with depressive symptoms in Black older adults

OBJECTIVES

Black older adults have a higher vascular burden compared to non-Hispanic White (NHW) older adults, which may put them at risk for a form of depression known as vascular depression (VaDep). The literature examining VaDep in Black older adults is sparse. The current study addressed this important gap by examining whether vascular burden was associated with depressive symptoms in Black older adults.

METHODS

Participants included 113 Black older adults from the Healthy Brain Project, a substudy of the Health, Aging, and Body Composition Study. In multiple regression analyses, clinical vascular burden (sum of vascular conditions) and white matter hyperintensity (WMH) volume predicted depressive symptoms as measured by the Center for Epidemiologic Studies Depression Scale, controlling for demographic variables. Follow-up analyses compared the associations in the Black subsample and in 179 NHW older adults.

RESULTS

Higher total WMH volume, but not clinically-defined vascular burden, predicted higher concurrent depressive symptoms and higher average depressive symptoms over 4 years. Similar associations were found between uncinate fasciculus (UF) WMHs and concurrent depressive symptoms and between superior longitudinal fasciculus WMHs and average depressive symptoms. The association between depressive symptoms and UF WMH was stronger in Black compared to NHW individuals.

CONCLUSION

This research is consistent with the VaDep hypothesis and extends it to Black older adults, a group that has historically been underrepresented in the literature. Results highlight WMH in the UF as particularly relevant to depressive symptoms in Black older adults and suggest this group may be particularly vulnerable to the negative effects of WMH.

Neuroimaging features of depression-frailty phenotype in older adults: a pilot study

OBJECTIVE

Frailty and late-life depression (LLD) often coexist and share several structural brain changes. We aimed to study the joint effect LLD and frailty have on brain structure.

DESIGN

Cross-sectional study.

SETTING

Academic Health Center.

PARTICIPANTS

Thirty-one participants (14 LLD+Frail and 17 Never-depressed+Robust).

MEASUREMENT

LLD was diagnosed by a geriatric psychiatrist according to the Diagnostic and Statistical Manual of Mental Disorders 5th edition for single episode or recurrent major depressive disorder without psychotic features. Frailty was assessed using the FRAIL scale (0-5), classifying subjects as robust (0), prefrail (1-2), and frail (3-5). Participants underwent T1-weighted magnetic resonance imaging in which covariance analysis of subcortical volumes and vertex-wise analysis of cortical thickness values were performed to access changes in grey matter. Participants also underwent diffusion tensor imaging in which tract-based spatial statistics was used with voxel-wise statistical analysis on fractional anisotropy and mean diffusion values to assess changes in white matter (WM).

RESULTS

We found a significant difference in mean diffusion values (48,225 voxels; peak voxel: pFWER=0.005, MINI coord. (X,Y,Z) = -26,-11,27) between the LLD-Frail group and comparison group. The corresponding effect size (f=0.808) was large.

CONCLUSION

We showed the LLD+Frailty group is associated with significant microstructural changes within WM tracts compared to Never-depressed+Robust individuals. Our findings indicate the possibility of a heightened neuroinflammatory burden as a potential mechanism underlying the co-occurrence of both conditions and the possibility of a depression-frailty phenotype in older adults.

Brain-cognition relationships in late-life depression: a systematic review of structural magnetic resonance imaging studies

BACKGROUND

Most patients with late-life depression (LLD) have cognitive impairment, and at least one-third meet diagnostic criteria for mild cognitive impairment (MCI), a prodrome to Alzheimer's dementia (AD) and other neurodegenerative diseases. However, the mechanisms linking LLD and MCI, and brain alterations underlying impaired cognition in LLD and LLD + MCI remain poorly understood.

METHODS

To address this knowledge gap, we conducted a systematic review of studies of brain-cognition relationships in LLD or LLD + MCI to identify circuits underlying impaired cognition in LLD or LLD + MCI. We searched MEDLINE, PsycINFO, EMBASE, and Web of Science databases from inception through February 13, 2023. We included studies that assessed cognition in patients with LLD or LLD + MCI and acquired: (1) T1-weighted imaging (T1) measuring gray matter volumes or thickness; or (2) diffusion-weighted imaging (DWI) assessing white matter integrity. Due to the heterogeneity in studies, we only conducted a descriptive synthesis.

RESULTS

Our search identified 51 articles, resulting in 33 T1 studies, 17 DWI studies, and 1 study analyzing both T1 and DWI. Despite limitations, reviewed studies suggest that lower thickness or volume in the frontal and temporal regions and widespread lower white matter integrity are associated with impaired cognition in LLD. Lower white matter integrity in the posterior cingulate region (precuneus and corpus callosum sub-regions) was more associated with impairment executive function and processing speed than with memory.

CONCLUSION

Future studies should analyze larger samples of participants with various degrees of cognitive impairment and go beyond univariate statistical models to assess reliable brain-cognition relationships in LLD.

Associations of neuroimaging markers with depressive symptoms over time in middle-aged and elderly persons

BACKGROUND

Cerebrovascular disease is regarded as a potential cause of late-life depression. Yet, evidence for associations of neuroimaging markers of vascular brain disease with depressive symptoms is inconclusive. We examined the associations of neuroimaging markers and depressive symptoms in a large population-based study of middle-aged and elderly persons over time.

METHODS

A total of 4943 participants (mean age = 64.6 ± 11.1 years, 55.7% women) from the Rotterdam Study were included. At baseline, total brain volume, gray matter volume, white matter volume, white matter hyperintensities volume, cortical infarcts, lacunar infarcts, microbleeds, white matter fractional anisotropy, and mean diffusivity (MD) were measured with a brain MRI (1.5T). Depressive symptoms were assessed twice with the Center for Epidemiologic Studies Depression scale (median follow-up time: 5.5 years, IQR = 0.9). To assess temporal associations of neuroimaging markers and depressive symptoms, linear mixed models were used.

RESULTS

A smaller total brain volume (β = -0.107, 95% CI -0.192 to -0.022), larger white matter hyperintensities volume (β = 0.047, 95% CI 0.010-0.084), presence of cortical infarcts (β = 0.194, 95% CI 0.047-0.341), and higher MD levels (β = 0.060, 95% CI 0.022-0.098) were cross-sectionally associated with more depressive symptoms. Longitudinal analyses showed that small total brain volume (β = -0.091, 95% CI -0.167 to -0.015) and presence of cortical infarcts (β = 0.168, 95% CI 0.022-0.314) were associated with increasing depressive symptoms over time. After stratification on age, effect sizes were more pronounced at older ages.

CONCLUSIONS

Neuroimaging markers of white matter microstructural damage were associated with depressive symptoms longitudinally in this study of middle-aged and elderly persons. These associations were more pronounced at older ages, providing evidence for the role of white matter structure in late-life depressive symptomatology.

Comparative study of magnetic resonance imaging-based neuroimaging methods in older adults with depression

BACKGROUND

Older patients with depression often have accompanying physical diseases, thus, their disease situation is more complex than that of younger people. The medical community has aimed for earlier diagnosis of senile depression due to ineffective treatment and eventual cognitive impairment.

METHOD

Neuroimaging markers of senile depression were identified through the systematic analysis of multimodal data including resting-state functional MRI (rs-fMRI) and structural MRI (sMRI), and compared with clinical neural scales between older participants with and without depression.

RESULTS

Morphological analysis of gray matter by MRI showed significantly enlarged volumes in the left inferior temporal gyrus and right talus fissure, and reduced volumes in the left parahippocampal gyrus and lentiform globus pallidus in the older depression group compared with those in the control group. Comparison of fractional amplitude of low-frequency fluctuation between the groups showed increased partial brain activity in the left posterior central gyrus and right anterior central gyrus in the depression group compared with those in the control group.

CONCLUSION

Older patients with depression showed significant organic changes and significantly increased local brain activity. There was a positive correlation between the intensity of local brain activity in the superior occipital gyrus and the Hamilton Depression Rating Scale scores.

GUIDING SIGNIFICANCE

It is important to assess the organic changes and the degree of brain activity in specific brain regions in the clinical diagnosis of depression in the older adults, to adjust treatment plans early according to the incidence.

A meta-analysis on the uncinate fasciculus in depression

Aberrant microstructure of the uncinate fasciculus (UNC), a white matter (WM) tract implicated in emotion regulation, has been hypothesized as a neurobiological mechanism of depression. However, studies testing this hypothesis have yielded inconsistent results. The present meta-analysis consolidates evidence from 44 studies comparing fractional anisotropy (FA) and radial diffusivity (RD), two metrics characterizing WM microstructure, of the UNC in individuals with depression (n = 5016) to healthy individuals (n = 18 425). We conduct meta-regressions to identify demographic and clinical characteristics that contribute to cross-study heterogeneity in UNC findings. UNC FA was reduced in individuals with depression compared to healthy individuals. UNC RD was comparable between individuals with depression and healthy individuals. Comorbid anxiety explained inter-study heterogeneity in UNC findings. Depression is associated with perturbations in UNC microstructure, specifically with respect to UNC FA and not UNC RD. The association between depression and UNC microstructure appears to be moderated by anxiety. Future work should unravel the cellular mechanisms contributing to aberrant UNC microstructure in depression; clarify the relationship between UNC microstructure, depression, and anxiety; and link UNC microstructure to psychological processes, such as emotion regulation.

Elevated homocysteine levels, white matter abnormalities and cognitive impairment in patients with late-life depression

Background

Cognitive impairment in late−life depression (LLD) is considered to be caused by neurodegenerative changes. Elevated homocysteine (Hcy) levels may be linked to cognitive abnormalities associated with LLD. The important role of white matter (WM) damage in cognitive impairment and pathogenesis in patients with LLD has been widely reported. However, no research has explored the interrelationships of these features in patients with LLD.

Objective

The goal of the study was to examine the interrelationship between Hcy levels, cognition, and variations in WM microstructure detected by diffusion tensor imaging (DTI) in patients with LLD.

Methods

We recruited 89 healthy controls (HCs) and 113 patients with LLD; then, we measured the plasma Hcy levels of participants in both groups. All individuals performed a battery of neuropsychological tests to measure cognitive ability. Seventy-four patients with LLD and 68 HCs experienced a DTI magnetic resonance imaging (MRI) scan.

Results

Patients with LLD showed significantly lower fractional anisotropy (FA) values in the bilateral inferior longitudinal fasciculus than those of healthy participants. Only in LLD patients was Hcy concentration inversely associated to FA values in the forceps minor. Finally, multiple regression analyses showed that an interaction between Hcy levels and FA values in the right cingulum of the cingulate cortex and right inferior longitudinal fasciculus were independent contributors to the executive function of patients with LLD.

Conclusion

Our results highlight the complex interplay between elevated homocysteine levels and WM abnormalities in the pathophysiology of LLD-related cognitive impairment, consistent with the neurodegeneration hypothesis.

Transdiagnostic role of glutamate and white matter damage in neuropsychiatric disorders: A Systematic Review

Neuropsychiatric disorders including generalized anxiety disorder (GAD), obsessive-compulsive disorder (OCD), major depressive disorder (MDD), bipolar disorder (BD), and schizophrenia (SZ) have been considered distinct categories of diseases despite their overlapping characteristics and symptomatology. We aimed to provide an in-depth review elucidating the role of glutamate/Glx and white matter (WM) abnormalities in these disorders from a transdiagnostic perspective. The PubMed online database was searched for studies published between 2010 and 2021. After careful screening, 401 studies were included. The findings point to decreased levels of glutamate in the Anterior Cingulate Cortex in both SZ and BD, whereas Glx is elevated in the Hippocampus in SZ and MDD. With regard to WM abnormalities, the Corpus Callosum and superior Longitudinal Fascicle were the most consistently identified brain regions showing decreased fractional anisotropy (FA) across all the reviewed disorders, except GAD. Additionally, the Uncinate Fasciculus displayed decreased FA in all disorders, except OCD. Decreased FA was also found in the inferior Longitudinal Fasciculus, inferior Fronto-Occipital Fasciculus, Thalamic Radiation, and Corona Radiata in SZ, BD, and MDD. Decreased FA in the Fornix and Corticospinal Tract were found in BD and SZ patients. The Cingulum and Anterior Limb of Internal Capsule exhibited decreased FA in MDD and SZ patients. The results suggest a gradual increase in severity from GAD to SZ defined by the number of brain regions with WM abnormality which may be partially caused by abnormal glutamate levels. WM damage could thus be considered a potential marker of some of the main neuropsychiatric disorders.

Default mode network dissociation linking cerebral beta amyloid retention and depression in cognitively normal older adults

Cerebral beta amyloid (Aβ) deposition and late-life depression (LLD) are known to be associated with the trajectory of Alzheimer's disease (AD). However, their neurobiological link is not clear. Previous studies showed aberrant functional connectivity (FC) changes in the default mode network (DMN) in early Aβ deposition and LLD, but its mediating role has not been elucidated. This study was performed to investigate the distinctive association pattern of DMN FC linking LLD and Aβ retention in cognitively normal older adults. A total of 235 cognitively normal older adults with (n = 118) and without depression (n = 117) underwent resting-state functional magnetic resonance imaging and ¹⁸F-flutemetamol positron emission tomography to investigate the associations between Aβ burden, depression, and DMN FC. Independent component analysis showed increased anterior DMN FC and decreased posterior DMN FC in the depression group compared with the no depression group. Global cerebral Aβ retention was positively correlated with anterior and negatively correlated with posterior DMN FC. Anterior DMN FC was positively correlated with severity of depression, whereas posterior DMN FC was negatively correlated with cognitive function. In addition, the effects of global cerebral Aβ retention on severity of depression were mediated by subgenual anterior cingulate FC. Our results of anterior and posterior DMN FC dissociation pattern may be pivotal in linking cerebral Aβ pathology and LLD in the course of AD progression. Further longitudinal studies are needed to confirm the causal relationships between cerebral Aβ retention and LLD.

Brain-based mechanisms of late-life depression: Implications for novel interventions

Late-life depression (LLD) is a particularly debilitating illness. Older adults suffering from depression commonly experience poor outcomes in response to antidepressant treatments, medical comorbidities, and declines in daily functioning. This review aims to further our understanding of the brain network dysfunctions underlying LLD that contribute to disrupted cognitive and affective processes and corresponding clinical manifestations. We provide an overview of a network model of LLD that integrates the salience network, the default mode network (DMN) and the executive control network (ECN). We discuss the brain-based structural and functional mechanisms of LLD with an emphasis on their link to clinical subtypes that often fail to respond to available treatments. Understanding the brain networks that underlie these disrupted processes can inform the development of targeted interventions for LLD. We propose behavioral, cognitive, or computational approaches to identifying novel, personalized interventions that may more effectively target the key cognitive and affective symptoms of LLD.

Neural substrates for late-life depression: A selective review of structural neuroimaging studies

Recent neuroimaging studies have characterized the pathophysiology of late-life depression (LLD) as a dysfunction of the brain networks involved in the regulation of emotion, motivational behavior, cognitive control, executive function, and self-referential thinking. In this article, we reviewed LLD-associated structural neuroimaging markers such as white matter hyperintensity (WMH), white matter integrity measured by diffusion tensor imaging, cortical and subcortical volumes, and cortical thickness, which may provide a structural basis for brain network dysfunction in LLD. LLD was associated with greater severity or volumes of deep, periventricular, or overall WMH and with decreased white matter integrity in the brain regions belonging to the fronto-striatal-limbic circuits and reduced white matter tract integrity which connects these circuits, such as the cingulum, corpus callosum, or uncinate fasciculus. Decreased volumes or cortical thickness in the prefrontal cortex, orbitofrontal cortex, anterior and posterior cingulate cortex, several temporal and parietal regions, hippocampus, amygdala, striatum, thalamus, and the insula were associated with LLD. These structural neuroimaging findings were also associated with cognitive dysfunction, which is a prominent clinical feature in LLD. Several structural neuroimaging markers including the WMH burden, white matter integrity, and cortical and subcortical volumes predicted antidepressant response in LLD. These structural neuroimaging findings support the hypothesis that disruption of the brain networks involved in emotion regulation and cognitive processing by impaired structural connectivity is strongly associated with the pathophysiology of LLD.

Memantine can protect against inflammation-based cognitive decline in geriatric depression

INTRODUCTION

Geriatric depression is frequently accompanied by cognitive complaints and inflammation that increase risk for treatment-resistant depression and dementia. Memantine, a neuroprotective drug, can improve depression, inflammation, and help prevent cognitive decline. In our six-month clinical trial, escitalopram/memantine (ESC/MEM) improved mood and cognition compared to escitalopram/placebo treatment (ESC/PBO; NCT01902004). In this report, we examined the impact of baseline inflammation on mood and cognitive outcomes.

MATERIALS AND METHODS

We measured a panel of inflammatory cytokine markers using Human 38-plex magnetic cytokine/chemokine kits (EMD Millipore, HCYTMAG-60K-PX38) in 90 older adults 60 years and older with major depression enrolled in a 6-month double-blind placebo-controlled trial of escitalopram ​+ ​memantine (ESC/MEM) in depressed older adults with subjective memory complaints. Four cytokine factors were derived and linear models were estimated to examine the predictive ability of cytokine levels on treatment induced change in depression and cognition.

RESULTS

Of the 90 randomized participants, 62 completed the 6-month follow up assessment. Both groups improved significantly on depression severity (HAM-D score), but not on cognitive outcomes at six months. Cytokine factor scores were not significantly different between ESC/MEM (n ​= ​45) and ESC/PBO (n ​= ​45) at baseline. Pro-inflammatory biomarkers at baseline predicted a decline in executive functioning in the ESC/PBO group but not in the ESC/MEM group, interaction F(1,52) ​= ​4.63, p ​= ​.04.

DISCUSSION

In this exploratory analysis, the addition of memantine to escitalopram provided a protective effect on executive functioning in older depressed adults. Future studies are needed to replicate the association of cytokine markers to antidepressant and neuroprotective treatment-related change in cognition in geriatric depression.

Differences in Cerebral Structure Associated With Depressive Symptoms in the Elderly With Alzheimer's Disease

Background: Alzheimer's disease (AD) is characterized by global deterioration in multiple cognitive domains. In addition to cognitive impairment, depressive symptoms are common issues that trouble AD patients. The neuroanatomical basis of depressive symptoms in AD patients has yet to be elucidated. Method: Twenty AD patients and 22 healthy controls (HCs) were recruited for the present study. Depressive symptoms in AD patients and HCs were assessed according to the Hamilton Depression Rating Scale (HDRS). Anatomical structural differences were assessed between AD patients and HCs using voxel-based morphometry (VBM) and surface-based morphometry (SBM). Correlation analyses were conducted to investigate relationships between depressive symptoms and structural altered regions. Multiple pattern analysis using linear support vector machine (SVM) was performed in another independent cohort, which was collected from Alzheimer's Disease Neuroimaging Initiative (ADNI) data and contained 20 AD patients and 20 HCs, to distinguish AD patients from HCs. Results: Compared with HCs, AD patients exhibited global cerebral atrophy in gray matter volume (GMV) and cortical thickness, including frontal, parietal, temporal, occipital, and insular lobes. In addition, insular GMV was negatively correlated with depressive symptoms. Moreover, SVM-based classification achieved an accuracy of 77.5%, a sensitivity of 70%, and a specificity of 85% by leave-one-out cross-validation. Conclusion: GMV of the insula displayed atrophy among AD patients, which is associated with depressive symptoms. Our observations provide a potential neural substrate for analysis to examine the co-occurrence of AD with depressive symptoms.

Evidence for Structural and Functional Alterations of Frontal-Executive and Corticolimbic Circuits in Late-Life Depression and Relationship to Mild Cognitive Impairment and Dementia: A Systematic Review

Depression is a risk factor for developing Alzheimer's disease and Related Dementia (ADRD). We conducted a systematic review between 2008 and October 2018, to evaluate the evidence for a conceptual mechanistic model linking depression and ADRD, focusing on frontal-executive and corticolimbic circuits. We focused on two neuroimaging modalities: diffusion-weighted imaging measuring white matter tract disruptions and resting-state functional MRI measuring alterations in network dynamics in late-life depression (LLD), mild cognitive impairment (MCI), and LLD+MCI vs. healthy control (HC) individuals. Our data synthesis revealed that in some but not all studies, impairment of both frontal-executive and corticolimbic circuits, as well as impairment of global brain topology was present in LLD, MCI, and LLD+MCI vs. HC groups. Further, posterior midline regions (posterior cingulate cortex and precuneus) appeared to have the most structural and functional alterations in all patient groups. Future cohort and longitudinal studies are required to address the heterogeneity of findings, and to clarify which subgroups of people with LLD are at highest risk for developing MCI and ADRD.

Changes of Altruistic Behavior and Kynurenine Pathway in Late-Life Depression

BACKGROUND

Depressive patients show less altruistic behavior. While, older adults present higher tendencies for altruism than younger adults. Depression and age are two of the influencing factors of altruism, kynurenine (KYN), and its metabolites. However, the characteristics of altruism in late-life depression (LLD) and its possible underlying mechanism have not been studied.

OBJECTIVE

We aimed to explore the characteristics of altruism in LLD patients and its neurobiological mechanism and structural brain network. We investigated whether the levels of metabolites in kynurenine pathway (KP) and white matter (WM) network topological features would influence the altruistic behavior in LLD patients.

METHODS

Thirty-four LLD patients and 36 heathy controls (HCs) were included. Altruism was evaluated by the Dictator Game (DG) paradigm. Serum concentrations of KP metabolites were detected by the liquid chromatography-tandem mass spectrometry method. The topological features of the WM network were calculated from diffusion tensor imaging data in conjunction with graph-theoretical analysis.

RESULTS

The LLD participants exhibited a higher level of altruism and WM global network properties than the HCs. Kynurenic acid to kynurenine (KYNA/KYN) ratio was associated with the DG performance in LLD group. KYNA/KYN ratio was associated with the WM network properties in HC group.

CONCLUSIONS

KYN metabolism played an important role in altruistic behavior in LLD.

The oblique effect: The relationship between profiles of visuospatial preference, cognition, and brain connectomics in older adults

The oblique effect (OE) describes the visuospatial advantage for identifying stimuli oriented horizontally or vertically rather than diagonally; little is known about brain aging and the OE. We investigated this relationship using the Judgment of Line Orientation (JLO) in 107 older adults (∼age = 67.8 ± 6.6; 51% female) together with neuropsychological tests of executive functioning (EF), attention/information processing (AIP), and neuroimaging. Only JLO lines falling between 36-54° or 126-144° were considered oblique. To quantify the oblique effect, we calculated z-scores for oblique errors (zOblique = #oblique errors/#oblique lines), and similarly, horizontal + vertical line errors (zHV), and a composite measure of oblique relative to HV errors (zOE). Composite z-scores of EF and AIP reflected domains associated with JLO performance. Graph theory analysis integrated T1-derived volumetry and diffusion MRI-derived white matter tractography into connectivity matrices analyzed for select network properties. Participants produced more zOblique than zHV errors (p < 0.001). Age was not associated with zOE adjusting for sex, education, and MMSE. Similarly adjusted linear regression models revealed that lower EF was associated with a larger oblique effect (p < 0.001). Modular analyses of neural connectivity revealed a differential patterns of network affiliation that varied by high versus low group status determined via median split of zOblique and zHV errors, separately. Older adults exhibit the oblique effect and it is associated with specific cognitive processes and regional brain networks that may facilitate future investigations of visuospatial preference in aging.

Mechanisms Linking White Matter Lesions, Tract Integrity, and Depression in Alzheimer Disease

OBJECTIVE

Late-life depression involves the disconnection of white matter tracts that regulate mood. A pathogenic link between poor tract integrity and depressive symptoms is believed to be white matter lesions (WML), however the mechanisms linking tract integrity, WML, and depression remains unexplored. The authors sought to identify whether the association between reduced tract integrity and depressive symptoms is mediated by WML in patients with Alzheimer disease (AD), and whether individual characteristics moderate this effect.

METHODS

This was a cross-sectional study in a tertiary memory clinic. A total of 91 patients with mild AD and 79 healthy elderly, comparable in depressive symptoms, white matter hyperintensities (WMH) volume, cardiovascular risk, age, and sex were chosen. Tract integrity was assessed using diffusion tensor imaging, WML were indexed as WMH, measured using fluid-attenuation inversion recovery imaging, and depressive symptoms were measured with the informant-based Geriatric Depression Scale.

RESULTS

In patients with mild AD, reduced tract integrity in right hemispheric cortical-subcortical tracts and the genu of the corpus callosum was moderately associated with depressive symptoms. This association was fully mediated by WML. Moderation analysis indicated that old age strengthened the association between all tracts and depressive symptoms, as mediated by WML. In cognitively healthy elderly, neither tracts nor WML were related to depressive symptoms.

CONCLUSION

Reduced tract integrity may be important but not sufficient for the manifestation of depressive symptoms in mild AD. Instead, WML may drive the pathogenic link between reduced tract integrity and depressive symptoms.

Linking late life depression and Alzheimer's disease: mechanisms and resilience

Purpose of Review

This review summarizes recent literature linking Alzheimer's disease (AD) and late life depression (LLD). It describes shared neurobiological features associated with both conditions, as well as factors that may increase resilience to onset and severity of cognitive decline and AD. Finally, we pose a number of future research directions toward improving detection, management, and treatment of both conditions.

Recent Findings

Epidemiological studies have consistently shown a significant relationship between LLD and AD, with support for depression as a prodromal feature of AD, a risk factor for AD, and observation of some shared risk factors underlying both disease processes. Three major neurobiological features shared by LLD and AD include neurodegeneration, disruption to cerebrovascular functioning, and increased levels of neuroinflammation. There are also potentially modifiable factors that can increase resilience to AD and LLD, including social support, physical and cognitive engagement, and cognitive reserve.

Summary

We propose that, in the context of depression, neurobiological events, such as neurodegeneration, cerebrovascular disease, and neuroinflammation result in a brain that is more vulnerable to the consequences of the pathophysiological features of AD, lowering the threshold for the onset of the behavioral presentation of AD (i.e., cognitive decline and dementia). We discuss factors that can increase resilience to AD and LLD, including social support, physical and cognitive engagement, and cognitive reserve. We conclude with a discussion of future research directions.

White matter abnormalities predict residual negative self-referential thinking following treatment of late-life depression with escitalopram: A preliminary study

BACKGROUND

Negative self-referential thinking is a common symptom of depression associated with poor treatment response. In late-life depression, white matter abnormalities may contribute to negative self-referential thoughts following antidepressant treatment. We investigated the association of fractional anisotropy (FA) in select regions of the negative valence system (NVS) with residual negative self-referential thoughts following treatment with escitalopram for late-life depression.

METHODS

The participants were older adults with major depression and psychiatrically normal controls. Depressed participants received 12 weeks of treatment with escitalopram. To assess self-referential thinking, participants completed a Trait Adjective Task at baseline and at week 12. Baseline MRI scans included a diffusion imaging sequence for FA analyses.

RESULTS

Participants with late-life depression differed from controls on all performance measures of the Trait Adjective Task at baseline and at 12 weeks. Depressed participants endorsed fewer negative personality traits and more positive personality traits at week 12 compared to baseline. Lower FA in the dorsal anterior cingulate and in the uncinate fasciculus in depressed participants was correlated with residual negative self-referential thinking (e.g., more endorsed negative adjectives, fewer rejected negative adjectives) at treatment end.

LIMITATIONS

The sample size is modest so the findings are preliminary. FA analyses were restricted to predetermined regions.

CONCLUSIONS

Negative self-referential thinking improved in depressed older adults following 12 weeks of treatment with escitalopram. Baseline FA in select white matter regions of the NVS was associated with residual negative self-referential thinking. These findings may help identify treatment targets for residual negative self-referential thoughts.

Aberrant Default Mode Network Underlying the Cognitive Deficits in the Patients With Late-Onset Depression

Late-onset depression (LOD) is regarded as a risk factor or a prodrome of Alzheimer’s disease (AD). Moreover, LOD patients with cognitive deficits have the higher risk of subsequent AD. Thus, it is necessary to understand the neural underpinnings of cognitive deficits and its pathological implications in LOD. Consistent findings show that the default mode network (DMN) is an important and potentially useful brain network for the cognitive deficits in LOD patients. In recent years, genetics has been actively researched as a possible risk factor in the pathogenesis of LOD. So, in this review, we discuss the current research progress on the cognitive deficits and DMN in LOD through a combined view of brain network and genetics. We find that different structural and functional impairments of the DMN might be involved in the etiological mechanisms of different cognitive impairments in LOD patients.

A Cross Sectional Examination of the Relation Between Depression and Frequency of Leisure Time Physical Exercise among the Elderly in Jinan, China

Depression has become a major global public health problem. Many studies have shown the positive effects of physical exercise on depression. However, few studies have examined the relationship between frequency of leisure time physical exercise and depression without considering the time and intensity of exercise among middle-aged and elderly people of urban communities in northern China. We conducted a cross-sectional survey that included 1604 participants among urban residents aged 50 years or older in China to evaluate how the frequency of physical exercise was related to depression. Our study showed that the prevalence of depression in the urban community of Jinan is 16.52%. For physical exercise, the odds ratios (ORs) and 95% confidence intervals (CIs) for 1~2 times per week, 3~4 times per week and ≥5 times per week were 1.137 (0.661, 1.953), 0.516 (0.304, 0.875) and 0.548 (0.392, 0.768) respectively, with adjustment for age, gender, marital status, BMI, hypertension, previously diagnosed type 2 diabetes, triglyceride, total cholesterol, soy food intake, milk food intake, vegetable and fruit intake and meat intake. We concluded that physically exercising three times a week is associated with a low prevalence of depression.

State of the Science of Neural Systems in Late-Life Depression: Impact on Clinical Presentation and Treatment Outcome

Major depression in older adults, or late-life depression (LLD), is a common and debilitating psychiatric disorder that increases the risk of morbidity and mortality. Although the effects of LLD make it important to achieve a diagnosis and start treatment quickly, individuals with LLD are often inadequately or unsuccessfully treated. The latest treatment developments suggest that interventions targeting executive dysfunction and neuroticism, constructs associated with poor response to antidepressants in older adults, are successful in treating LLD. Specific behavioral interventions (computerized cognitive training, mindfulness meditation, aerobic exercise) appear to decrease depressive symptoms and ameliorate executive dysfunction and neuroticism, but we do not fully understand the mechanisms by which these treatments work. We review recent research on neural network changes underlying executive dysfunction and neuroticism in LLD and their association with clinical outcomes (e.g., treatment response, cognitive functioning).

The efficacy of transcranial random noise stimulation (tRNS) on mood may depend on individual differences including age and trait mood

OBJECTIVES

To assess whether changes in brain microstructures associated with ageing and presence of cardiovascular risk factors (CVRF) reduce the efficacy of transcranial electrical stimulation (tES) improving mood in euthymic older adults.

METHODS

Using excitatory high-frequency transcranial random noise stimulation (tRNS) over bilateral dorsolateral prefrontal cortex, the effect on mood was assessed in euthymic young adults (YA), older adults (HOA) and older adults with CVRF (OVR). Active-tRNS or sham was applied over two sessions. Positive and Negative Affect Schedule and Warwick Edinburgh Mental Well-being Scale measured self-reported state mood before and after stimulation. Trait mood was also measured using the Geriatric Depression Scale.

RESULTS

Response to tRNS seemed dependent on individual differences in age and trait mood. In HOA, more negative trait mood was associated with more positive mood change after tRNS. OVR showed a similar but reduced pattern of mood change to HOA. In YA, more positive trait mood was associated with greater positive mood change after tRNS.

CONCLUSIONS

Age and trait mood may be important factors when examining the efficacy of tES as an alternative treatment for depression.

SIGNIFICANCE

Future studies should consider how response to tES is affected by individual differences.

Impaired Frontolimbic Connectivity and Depressive Symptoms in Patients with Alzheimer's Disease

BACKGROUND/AIMS

Depressive symptoms are commonly observed in Alzheimer's disease (AD). The underlying mechanisms of depressive symptoms in AD remain unclear; frontolimbic circuitry dysfunction may play a role. We aimed to investigate the microstructural integrity of frontolimbic connectivity of specific fiber tracts in AD patients with and without depressive symptoms using diffusion tensor imaging (DTI).

METHODS

Eleven AD patients with depressive symptoms (dep-AD), 18 AD patients without depressive symptoms (nondep-AD), and 18 normal control (NC) subjects were included. The cingulum bundle (CB), uncinate fasciculus (UF), and fornix, mainly frontolimbic connectivity, were measured by DTI tractography and the metrics of fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity, and radial diffusivity (RD) were calculated.

RESULTS

Compared with NC subjects, both dep-AD and nondep-AD patients showed significant differences for all indices in the fornix and significantly decreased FA and increased MD and RD in the bilateral CB and UF. When compared to nondep-AD patients, dep-AD patients showed significantly increased MD and RD in the bilateral CB and right UF.

CONCLUSION

Depressive symptoms in AD patients may be involved in greater microstructural abnormalities of frontolimbic connectivity and myelin injury in the bilateral CB and right UF might contribute to the pathophysiology of depressive symptoms in AD.

Associations between pro-inflammatory cytokines, learning, and memory in late-life depression and healthy aging

OBJECTIVES

Pro-inflammatory cytokines may play a role in learning and memory difficulties and may be exacerbated in late-life depression (LLD), where pro-inflammatory markers are already elevated because of aging and age-related vascular risk.

METHODS

Learning and memory, and pro-inflammatory cytokines-Interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and Interleukin-6 (IL-6) were measured in 24 individuals with LLD and 34 healthy older adults (HOA). Hippocampal volumes were segmented using Freesurfer software.

RESULTS

Pro-inflammatory cytokines were higher in LLD compared with HOA. Regression analyses demonstrated that educational level and right hippocampal volume significantly contributed to explaining the variance in learning. For memory performance, educational level, right hippocampal volume and a group-by-IL-6 interaction significantly contributed to the model.

CONCLUSIONS

High levels of IL-6 impact cognition in LLD but not HOA. Results suggest that high levels of inflammation alone are not sufficient to account for cognitive difficulties, but may interact with other factors in at-risk populations like LLD, to contribute to memory difficulties. Copyright © 2017 John Wiley & Sons, Ltd.

Mnemonic function in small vessel disease and associations with white matter tract microstructure

Cerebral small vessel disease (SVD) is associated with deficits in working memory, with a relative sparing of long-term memory; function may be influenced by white matter microstructure. Working and long-term memory were examined in 106 patients with SVD and 35 healthy controls. Microstructure was measured in the uncinate fasciculi and cingula. Working memory was more impaired than long-term memory in SVD, but both abilities were reduced compared to controls. Regression analyses found that having SVD explained the variance in memory functions, with additional variance explained by the cingula (working memory) and uncinate (long-term memory). Performance can be explained in terms of integrity loss in specific white matter tract associated with mnemonic functions.

Brain levels of high-energy phosphate metabolites and executive function in geriatric depression

OBJECTIVES

Depression in late life has been associated with difficulties in cognitive processing, particularly in the domains of executive function, processing speed and memory, and increases the risk of developing dementia suggesting a neurodegenerative phenotype. Mitochondrial dysfunction is frequently an early event in neurodegenerative illnesses and may be operative in patients with late life depression. Phosphorus magnetic resonance spectroscopy (31P MRS) allows for the quantification of bioenergetic molecules produced by mitochondria.

METHODS

Ten patients with late life depression and eight normal elderly controls were studied with Stroop color and interference tests, which are widely used measures of processing speed and executive function, respectively, followed by (31P) MRS 3-dimensional chemical-shift imaging measuring levels of adenosine triphosphate, phosphocreatine, inorganic phosphate, and pH over the whole brain.

RESULTS

In all subjects, gray matter phosphocreatine was positively associated with Stroop interference. Levels of white matter adenosine triphosphate were associated with Stroop interference in subjects with late life depression but not normal elderly. There was also a complementary association between white matter inorganic phosphate and Stroop interference in late life depression patients.

CONCLUSIONS

These findings suggest two independent sources of executive function dependence on bioenergetic state in the aging brain. The dependence of executive function performance in subjects with late life depression on ATP in white matter may be associated with mitochondrial impairment and is consistent with predictions of the vascular depression hypothesis. Further research with wider neuropsychological testing targeting bioenergetic markers could help clarify the scope of these effects. Copyright © 2016 John Wiley & Sons, Ltd.

Cognitive and connectome properties detectable through individual differences in graphomotor organization

We investigated whether graphomotor organization during a digitized Clock Drawing Test (dCDT) would be associated with cognitive and/or brain structural differences detected with a tractography-derived structural connectome of the brain. 72 non-demented/non-depressed adults were categorized based on whether or not they used 'anchor' digits (i.e., 12, 3, 6, 9) before any other digits while completing dCDT instructions to "draw the face of a clock with all the numbers and set the hands to 10 after 11". 'Anchorers' were compared to 'non-anchorers' across dCDT, additional cognitive measures and connectome-based metrics. In the context of grossly intact clock drawings, anchorers required fewer strokes to complete the dCDT and outperformed non-anchorers on executive functioning and learning/memory/recognition tasks. Anchorers had higher local efficiency for the left medial orbitofrontal and transverse temporal cortices as well as the right rostral anterior cingulate and superior frontal gyrus versus non-anchorers suggesting better regional integration within local networks involving these regions; select aspects of which correlated with cognition. Results also revealed that anchorers' exhibited a higher degree of modular integration among heteromodal regions of the ventral visual processing stream versus non-anchorers. Thus, an easily observable graphomotor distinction was associated with 1) better performance in specific cognitive domains, 2) higher local efficiency suggesting better regional integration, and 3) more sophisticated modular integration involving the ventral ('what') visuospatial processing stream. Taken together, these results enhance our knowledge of the brain-behavior relationships underlying unprompted graphomotor organization during dCDT.

White matter hyperintensities are associated with the severity of late-life somatoform disorders and executive functions

BACKGROUND

Medically unexplained symptoms are often seen in the elderly. Recently, correlations between medically unexplained symptoms and somatoform disorders (SDs) have been reported. The existence of many interactive psychiatric aetiologies is known among SDs. Late-life SDs might be influenced by some aetiological factors caused by ageing processes, such as structural changes in the brain and cognitive dysfunctions.

AIMS

Under such circumstances, we investigated the presence of subcortical white matter hyperintensities (WMHs), which increase with ageing, and hypothesized that subcortical WMHs are related to the disease severity of late-life SDs. Furthermore, we confirmed whether cognitive dysfunction influences this process.

METHODS

To evaluate these hypotheses, we examined patients with medically unexplained symptoms who met the criteria for undifferentiated somatoform disorder and divided the patients into three groups according to the degree of subcortical WMHs: grade 0, grade 1, and grade 2. The subcortical WMHs were rated using Fazekas grading. Differences in symptom severity and cognitive functions were compared among the three groups.

RESULTS

The grade 2 group had the severest symptoms. Furthermore, the grade 2 group had lower cognitive function scores than the other groups.

CONCLUSIONS

The present study showed that the presence of subcortical WMHs in patients with late-life SDs was a predictor of disease severity. Moreover, cognitive dysfunction appeared to play a role in the advancement of disease severity.

Brain connectivity in late-life depression and aging revealed by network analysis

OBJECTIVE

To use novel methods to examine age associations across an integrated brain network in healthy older adults (HOA) and individuals with late-life depression (LLD). Graph theory metrics describe the organizational configuration of both the global network and specified brain regions.

METHODS

Cross-sectional data were acquired. Graph theory was used to explore diffusion tensor imaging-derived white matter networks. Forty-eight HOA and 28 adults with LLD were recruited from the community. Global and local metrics in prefrontal, cingulate, and temporal regions were calculated. Group differences and associations with age were explored.

RESULTS

Group differences were noted in local metrics of the right prefrontal and temporal regions, but no significant differences were observed on global metrics. Local (not global) metrics were associated with age differently across groups. For HOA, local metrics across all regions correlated with age, whereas in adults with LLD, correlations were only observed within temporal regions. In keeping with hypothesized regions impacted by LLD, stronger hubs in right temporal regions were observed among HOA, whereas LLD individuals were characterized by robust hubs in frontal regions.

CONCLUSION

We demonstrate widespread age-related changes in local network properties among HOA with different and more restricted local changes in LLD. Although a preliminary analysis, different patterns of correlations in local networks coupled with equivalent global metrics may reflect altered local structural brain networks in patients with LLD.

Limbic white matter microstructure plasticity reflects recovery from depression

BACKGROUND

White matter microstructure alterations of limbic and reward pathways have been reported repeatedly for depressive episodes in major depressive disorder (MDD) and bipolar disorder (BD). However, findings during remission are equivocal. It was the aim of this study to investigate if white matter microstructure changes during the time course of clinical remission.

METHODS

Fifteen depressed patients (11 MDD, 4 BD) underwent diffusion-weighted MRI both during depression, and during remission following successful antidepressive treatment (average time interval between scans = 6 months). Fractional anisotropy (FA) was sampled along reconstructions of the supero-lateral medial forebrain bundle (slMFB), the cingulum bundle (CB), the uncinate fasciculus (UF), the parahippocampal cingulum (PHC) and the fornix. Repeated measures ANCOVAs controlling for the effect of age were calculated for each tract.

RESULTS

There was a significant main effect of time (inter-scan interval) for mean-FA for the right CB and for the left PHC. For both pathways there was a significant time × age interaction. In the right CB, FA increased in younger patients, while FA decreased in older patients. In the left PHC, a reverse pattern was seen. FA changes in the right CB correlated positively with symptom reductions. Mean-FA of UF, slMFB and fornix did not change between the two time points.

LIMITATIONS

All patients were medicated, sample size, and lack of control group.

CONCLUSIONS

Right CB and left PHC undergo age-dependent plastic changes during the course of remission and may serve as a state marker in depression. UF, slMFB and FO microstructure remains stable.

Diffusion tensor imaging studies in late-life depression: systematic review and meta-analysis

OBJECTIVES

Late-life depression (LLD) is the association with more cerebrovascular susceptibilities and white matter damage that can be assessed with diffusion tensor imaging (DTI). To better understand the white matter pathological alterations in LLD, we conducted a systematic review and meta-analysis.

METHODS

We searched MEDLINE, EMBASE, PsycINFO, PubMed, and Google Scholar databases for DTI studies comparing patients with LLD and healthy controls. For each study, details regarding participants, imaging methods, and results were extracted. Fractional anisotropy, an index of white matter integrity, was the dependent variable for group comparison. Effect sizes indicating the degree of group difference were estimated by random-effects meta-analysis.

RESULTS

A total of 15 eligible studies were included in the qualitative systematic review, nine of which were suitable for quantitative meta-analyses for the dorsolateral prefrontal cortex (DLPFC), corpus callosum, cingulum, and uncinate fasciculus (UF). Compared with the healthy control group, the LLD group showed lower fractional anisotropy in the DLPFC and UF with a large and a medium effect size, respectively, although heterogeneity and publication bias were found in the DLPFC.

CONCLUSION

Diffusion tensor imaging studies of LLD consistently showed reduced anisotropy in the DLPFC and UF of patients with LLD. These damaged regions are located with the frontostriatal and limbic networks. Thus, our findings showed that the disruption of frontal and frontal-to-limbic white matter tracts contributes to the pathogenesis of LLD.

Neuroanatomical correlates of apathy in late-life depression and antidepressant treatment response

BACKGROUND

Apathy is a prominent feature of geriatric depression that predicts poor clinical outcomes and hinders depression treatment. Yet little is known about the neurobiology and treatment of apathy in late-life depression. This study examined apathy prevalence in a clinical sample of depressed elderly, response of apathy to selective serotonin reuptake inhibitor (SSRI) treatment, and neuroanatomical correlates that distinguished responders from non-responders and healthy controls.

METHODS

Participants included 45 non-demented, elderly with major depression and 43 elderly comparison individuals. After a 2-week single-blind placebo period, depressed participants received escitalopram 10mg daily for 12 weeks. The Apathy Evaluation Scale (AES) and 24-item Hamilton Depression Rating Scale (HDRS) were administered at baseline and 12 weeks. MRI scans were acquired at baseline for concurrent structural and diffusion tensor imaging of anterior cingulate gray matter and associated white matter tracts.

RESULTS

35.5% of depressed patients suffered from apathy. This declined to 15.6% (p<0.1) following treatment, but 43% of initial sufferers continued to report significant apathy. Improvement of apathy with SSRI was independent of change in depression but correlated with larger left posterior subgenual cingulate volumes and greater fractional anisotropy of left uncinate fasciculi.

LIMITATIONS

Modest sample size, no placebo control, post-hoc secondary analysis, use of 1.5T MRI scanner

CONCLUSIONS

While prevalent in geriatric depression, apathy is separable from depression with regards to medication response. Structural abnormalities of the posterior subgenual cingulate and uncinate fasciculus may perpetuate apathetic states by interfering with prefrontal cortical recruitment of limbic activity essential to motivated behavior.