Imbalanced hippocampal functional networks associated with remitted geriatric depression and apolipoprotein E ε4 allele in nondemented elderly: a preliminary study

Association of functional connectivity of the executive control network or default mode network with cognitive impairment in older adults with remitted major depressive disorder or mild cognitive impairment

Major depressive disorder (MDD) is associated with an increased risk of developing dementia. The present study aimed to better understand this risk by comparing resting state functional connectivity (rsFC) in the executive control network (ECN) and the default mode network (DMN) in older adults with MDD or mild cognitive impairment (MCI). Additionally, we examined the association between rsFC in the ECN or DMN and cognitive impairment transdiagnostically. We assessed rsFC alterations in ECN and DMN in 383 participants from five groups at-risk for dementia-remitted MDD with normal cognition (MDD-NC), non-amnestic mild cognitive impairment (naMCI), remitted MDD + naMCI, amnestic MCI (aMCI), and remitted MDD + aMCI-and from healthy controls (HC) or individuals with Alzheimer's dementia (AD). Subject-specific whole-brain functional connectivity maps were generated for each network and group differences in rsFC were calculated. We hypothesized that alteration of rsFC in the ECN and DMN would be progressively larger among our seven groups, ranked from low to high according to their risk for dementia as HC, MDD-NC, naMCI, MDD + naMCI, aMCI, MDD + aMCI, and AD. We also regressed scores of six cognitive domains (executive functioning, processing speed, language, visuospatial memory, verbal memory, and working memory) on the ECN and DMN connectivity maps. We found a significant alteration in the rsFC of the ECN, with post hoc testing showing differences between the AD group and the HC, MDD-NC, or naMCI groups, but no significant alterations in rsFC of the DMN. Alterations in rsFC of the ECN and DMN were significantly associated with several cognitive domain scores transdiagnostically. Our findings suggest that a diagnosis of remitted MDD may not confer functional brain risk for dementia. However, given the association of rs-FC with cognitive performance (i.e., transdiagnostically), rs-FC may help in stratifying this risk among people with MDD and varying degrees of cognitive impairment.

Predicting conversion to Alzheimer's disease among individual high-risk patients using the Characterizing AD Risk Events index model

AIMS

Both amnestic mild cognitive impairment (aMCI) and remitted late-onset depression (rLOD) confer a high risk of developing Alzheimer's disease (AD). This study aims to determine whether the Characterizing AD Risk Events (CARE) index model can effectively predict conversion in individuals at high risk for AD development either in an independent aMCI population or in an rLOD population.

METHODS

The CARE index model was constructed based on the event-based probabilistic framework fusion of AD biomarkers to differentiate individuals progressing to AD from cognitively stable individuals in the aMCI population (27 stable subjects, 6 progressive subjects) and rLOD population (29 stable subjects, 10 progressive subjects) during the follow-up period.

RESULTS

AD diagnoses were predicted in the aMCI population with a balanced accuracy of 80.6%, a sensitivity of 83.3%, and a specificity of 77.8%. They were also predicted in the rLOD population with a balanced accuracy of 74.5%, a sensitivity of 80.0%, and a specificity of 69.0%. In addition, the CARE index scores were observed to be negatively correlated with the composite Z scores for episodic memory (R2  = .17, P < .001) at baseline in the combined high-risk population (N = 72).

CONCLUSIONS

The CARE index model can be used for the prediction of conversion to AD in both aMCI and rLOD populations effectively. Additionally, it can be used to monitor the disease severity of patients.

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.

Hippocampal atrophy and functional connectivity disruption in cirrhotic patients with minimal hepatic encephalopathy

The hippocampus is a crucial pathological node for minimal hepatic encephalopathy (MHE) and it is associated with various cognitive impairments. Investigations on alterations involving hippocampal morphology and functional connectivity (FC) in MHE are limited. This study aimed to simultaneously evaluate hippocampal volume and FC alterations and their association with cognitive decline in MHE. Twenty-two cirrhotic patients with MHE, 31 cirrhotic patients without MHE (NHE), and 43 healthy controls underwent high-resolution T1-weighted imaging, resting-state functional magnetic resonance imaging, and cognition assessment based on Psychometric Hepatic Encephalopathy Score (PHES). The structural images were preprocessed using a voxel-based morphometry method, during which hippocampal volume was measured. The hippocampal connectivity network was identified using seed-based correlation analysis. Hippocampal volume and FC strength were compared across the three groups and correlated against the PHES results of the cirrhotic patients. Compared to the controls, MHE patients exhibited a significantly lower bilateral hippocampal volume. A slight decrease in hippocampal volume was obtained from NHE to MHE, but it did not reach statistically significance. In addition, the average FC strength of the bilateral hippocampal connectivity network was significantly lower in the MHE patients. In particular, the MHE patients showed a decrease in FC involving the left hippocampus to bilateral posterior cingulate gyrus and left angular gyrus. The MHE patients also showed FC reduction between the right hippocampus and bilateral medial frontal cortex. A progressive reduction in hippocampal FC from NHE to MHE was also observed. The bilateral hippocampal FC strength (but not hippocampal volume) was positively correlated with the PHES results of the cirrhotic patients. Our assessment of MHE patients revealed decreased hippocampal volume, which suggests regional atrophy, and reduced hippocampal connectivity with regions that are primarily involved in the default-mode network, thereby suggesting a functional disconnection syndrome. These alterations reveal the mechanisms underlying cognitive deterioration with disease progression.

Shared genetic risk factors for depression and stroke

BACKGROUND

The comorbidity of major depressive disorder (MDD) and stroke are common in clinic. There is a growing body of evidence suggesting a bi-directional relationship between stroke and depression. However, the mechanisms underlying the relationship between MDD and stroke are poorly investigated. Considering that both MDD and stroke can be heritable and are influenced by multiple risk genes, shared genetic risk factors between MDD and stroke may exist.

OBJECTIVE

The objective is to review the existing evidence for common genetic risk factors for both MDD and stroke and to outline the possible pathophysiological mechanisms mediating this association.

METHODS

A systematic review and meta-analysis was performed. Gene association studies regarding stroke and depression were searched in the database PubMed, CNKI, and Chinese Biomedical Literature Database before December 2018. Statistical analysis was performed using the software Revman 5.3.

RESULTS

Genetic polymorphisms of 4 genes, methylenetetrahydrofolate reductase (MTHFR) and apolipoprotein E (ApoE) have been demonstrated to associate with the increased risk for both MDD and stroke, while the association between identified polymorphisms in angiotensin converting enzyme (ACE) and serum paraoxonase (PON1) with depression is still under debate, for the existing studies are insufficient in sample size. These results suggest the possible pathophysiological mechanisms that are common to these two disorders, including immune-inflammatory imbalance, increased oxidative and nitrative stress, dysregulation of lipoprotein and lipid metabolism, and changes of cerebrovascular morphology and function. Other associated genes with few or conflicting results have also been included, and a few studies have investigated the effects of the described polymorphisms on MDD and stroke comorbidity, such as post stroke depression.

CONCLUSION

These findings suggest that shared genetic pathways may contribute to the comorbidity of MDD and stroke. Studies to evaluate the shared genetic variations between MDD and stroke may provide insights into the molecular mechanisms that trigger disease progression.

The Contribution of Genetic Factors to Cognitive Impairment and Dementia: Apolipoprotein E Gene, Gene Interactions, and Polygenic Risk

Alzheimer's disease (AD) is a progressive neurodegenerative disease. Although it has been studied for years, the pathogenesis of AD is still controversial. Genetic factors may play an important role in pathogenesis, with the apolipoprotein E (APOE) gene among the greatest risk factors for AD. In this review, we focus on the influence of genetic factors, including the APOE gene, the interaction between APOE and other genes, and the polygenic risk factors for cognitive function and dementia. The presence of the APOE ε4 allele is associated with increased AD risk and reduced age of AD onset. Accelerated cognitive decline and abnormal internal environment, structure, and function of the brain were also found in ε4 carriers. The effect of the APOE promoter on cognition and the brain was confirmed by some studies, but further investigation is still needed. We also describe the effects of the associations between APOE and other genetic risk factors on cognition and the brain that exhibit a complex gene⁻gene interaction, and we consider the importance of using a polygenic risk score to investigate the association between genetic variance and phenotype.

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.

The apolipoprotein E gene affects the three-year trajectories of compensatory neural processes in the left-lateralized hippocampal network

Previous cross-sectional studies that investigated the effects of apolipoprotein E (ApoE) ε4 status on hippocampal networks have shown inconsistent results. Aging is a well-known risk factor for Alzheimer's disease (AD) and could strongly interact with ApoE-related vulnerabilities to affect AD risk. However, no longitudinal data have been published regarding the interaction of the ApoE genotype and aging on hippocampal networks. Fifty-one patients with amnestic-type mild cognitive impairment (aMCI) and 64 matched cognitively normal elderly subjects underwent resting-state fMRI scans and neuropsychological tests at baseline and at a 35-month follow-up. Hippocampal resting-state functional connectivity (FC) data were analyzed utilizing a mixed analysis of covariance with ApoE genotype, time points and disease as fixed factors, controlling for age, sex and years of education. The notable finding was that the FC between the left hippocampus and right frontal regions for ε4 carriers longitudinally increased in the normal subjects, but decreased in aMCI patients, whereas the FC for non-carriers was maintained in normal subjects but increased in aMCI patients. Specifically, the longitudinal increases in hippocampal FC with the right inferior frontal gyrus were positively correlated with the changes in episodic memory test scores in non-carriers with aMCI. The interaction between the ApoE genotype, aging and disease suggested that aging should be considered a key regulator of the impact of the ApoE genotype on the phenotypic variants of AD. These findings also demonstrated that compensatory neural processes were accelerated in genetically high risk individuals, but could be subsequently exhausted with the onset of cognitive impairment.

Functional segregation loss over time is moderated by APOE genotype in healthy elderly

We investigated the influence of the apolipoprotein E-ɛ4 allele (APOE-ɛ4) on longitudinal age-related changes in brain functional connectivity (FC) and cognition, in view of mixed cross-sectional findings. One hundred and twenty-two healthy older adults (aged 58-79; 25 APOE-ɛ4 carriers) underwent task-free fMRI scans at baseline. Seventy-eight (16 carriers) had at least one follow-up (every 2 years). Changes in intra- and internetwork FCs among the default mode (DMN), executive control (ECN), and salience (SN) networks, as well as cognition, were quantified using linear mixed models. Cross-sectionally, APOE-ɛ4 carriers had lower functional connectivity between the ECN and SN than noncarriers. Carriers also showed a stronger age-dependent decrease in visuospatial memory performance. Longitudinally, carriers had steeper increase in inter-ECN-DMN FC, indicating loss of functional segregation. The longitudinal change in processing speed performance was not moderated by APOE-ɛ4 genotype, but the brain-cognition association was. In younger elderly, faster loss of segregation was correlated with greater decline in processing speed regardless of genotype. In older elderly, such relation remained for noncarriers but reversed for carriers. APOE-ɛ4 may alter aging by accelerating the change in segregation between high-level cognitive systems. Its modulation on the longitudinal brain-cognition relationship was age-dependent.

Neuroimaging genomic studies in major depressive disorder: A systematic review

Genetic-neuroimaging studies could identify new potential endophenotypes of major depressive disorder (MDD). Morphological and functional alterations may be attributable to genetic factors that regulate neurogenesis and neurodegeneration. Given that the association between gene polymorphisms and brain morphology or function has varied across studies, this systematic review aims at evaluating and summarizing all available genetic-neuroimaging studies. Twenty-eight gene variants were evaluated in 64 studies by structural or functional magnetic resonance imaging. Significant genetic-neuroimaging associations were found in monoaminergic genes, BDNF genes, glutamatergic genes, HPA axis genes, and the other common genes, which were consistent with common hypotheses of the pathogenesis of MDD.

The Effect of Apolipoprotein E ε4 (APOE ε4) on Visuospatial Working Memory in Healthy Elderly and Amnestic Mild Cognitive Impairment Patients: An Event-Related Potentials Study

Background: Apolipoprotein E (APOE) ε4 is the only established risk gene for late-onset, sporadic Alzheimer’s disease (AD). Previous studies have provided inconsistent evidence for the effect of APOE ε4 status on the visuospatial working memory (VSWM).

Objective: The aim was to investigate the effect of APOE ε4 on VSWM with an event-related potential (ERP) study in healthy controls (HC) and amnestic mild cognitive impairment (aMCI) patients.

Methods: The study recorded 39 aMCI patients (27 APOE ε4 non-carriers and 12 APOE ε4 carriers) and their 43 matched controls (25 APOE ε4 non-carriers and 18 APOE ε4 carriers) with an 64-channel electroencephalogram. Participants performed an N-back task, a VSWM paradigm that manipulated the number of items to be stored in memory.

Results: The present study detected reduced accuracy and delayed mean correct response time (RT) in aMCI patients compared to HC. P300, a positive component that peaks between 300 and 500 ms, was elicited by the VSWM task. In addition, aMCI patients showed decreased P300 amplitude at the central–parietal (CP1, CPz, and CP2) and parietal (P1, Pz, and P2) electrodes in 0- and 1-back task compared to HC. In both HC and aMCI patients, APOE ε4 carriers showed reduced P300 amplitude with respect to non-carriers, whereas no significant differences in accuracy or RT were detected between APOE ε4 carriers and non-carriers. Additionally, standardized low-resolution brain electromagnetic tomography analysis (s-LORETA) showed enhanced brain activation in the right parahippocampal gyrus (PHG) during P300 time range in APOE ε4 carriers with respect to non-carriers in aMCI patients.

Conclusion: It demonstrated that P300 amplitude could predict VSWM deficits in aMCI patients and contribute to early detection of VSWM deficits in APOE ε4 carriers.

The characteristic of cognitive dysfunction in remitted late life depression and amnestic mild cognitive impairment

Remitted late life depression exhibits persistent cognitive impairments and enhances the risk of dementia. This study aimed to examine the characteristics of cognitive dysfunction in remitted late life depression and amnestic mild cognitive impairment (MCI). Remitted late life depression (n=61), amnestic MCI (n=61) and age-education-matched controls (n=65) were evaluated with a battery of neuropsychological tests grouped into executive function, memory, processing speed, attention and visuospatial domains. Compared with control subjects, amnestic MCI individuals showed more severe cognitive impairments in all domains, while remitted late life depression individuals performed worse in executive function and memory. The pattern of cognitive profiles significantly differed between remitted late life depression and amnestic MCI groups, which might be mainly attributed to worse impairments in memory and executive function in amnestic MCI individuals. Executive function was the core impaired cognitive domain mediating the influence of predictors on other cognitions in both remitted late life depression and amnestic MCI groups, which indicated a possible etiopathogenic mechanism underlying the conversion to dementia.

Disrupted Interhemispheric Synchrony in Default Mode Network Underlying the Impairment of Cognitive Flexibility in Late-Onset Depression

The intuitive association between cognitive impairment and aberrant functional activity in the brain network has prompted interest in exploring the role of functional connectivity in late-onset depression (LOD). The relationship of altered voxel-mirrored homotopic connectivity (VMHC) and cognitive dysfunction in LOD is not yet well understood. This study was designed to examine the implicit relationship between the disruption of interhemispheric functional coordination and cognitive impairment in LOD. LOD patients (N = 31) and matched healthy controls (HCs; N = 37) underwent neuropsychological tests and functional magnetic resonance imaging (fMRI) in this study. The intergroup difference of interhemispheric coordination was determined by calculating VMHC value in the whole brain. The neuro-behavioral relevancy approach was applied to explore the association between disrupted VMHC and cognitive measures. Receiver operating characteristic (ROC) curve analysis was used to determine the capability of disrupted regional VMHC to distinguish LOD. Compared to the HC group, significantly attenuated VMHC in the superior frontal gyrus (SFG), superior temporal gyrus (STG), posterior cerebellar lobe (CePL) and post- and precentral gyri were observed in the bilateral brain of LOD patients. The interhemispheric asynchrony in bilateral CePLs was positively correlated with the performance of trail making test B (TMT-B) in LOD patients (r = 0.367, P = 0.040). ROC analysis revealed that regions with abnormal VMHC could efficiently distinguish LOD from HCs (Area Under Curve [AUC] = 0.90, P < 0.001). Altered linkage patterns of intrinsic homotopic connectivity and impaired cognitive flexibility was first investigated in LOD, and it would provide a novel clue for revealing the neural substrates underlying cognitive impairment in LOD.

Hippocampal-DMN disconnectivity in MS is related to WM lesions and depression

The hippocampus is part of the default-mode network (DMN) and is functionally hit early in multiple sclerosis (MS). Hippocampal and DMN dysfunctions have been associated with depression, both in patients with MS and in major depressive disorders. We hypothesized that white matter lesions may contribute, through a disconnection mechanism, to hippocampal dysfunction. To test this, we assessed the relationship between hippocampal resting-state (RS) functional connectivity (FC) abnormalities with brain T2 lesion volumes and the presence and severity of depression. Structural and RS fMRI images were acquired from 69 patients with cognitively intact MS and 42 matched healthy controls (HC). Depression was quantified using the Montgomery-Asberg Depression Rating Scale. Seed-voxel hippocampal RS FC was assessed. SPM8 was used for between-group comparisons and correlation analysis between RS FC abnormalities with clinical and structural MRI variables. Compared to HC, patients with MS showed a significant atrophy of the whole brain and left hippocampus (P < 0.001), and a distributed pattern of decreased RS FC between the hippocampi and several cortical-subcortical regions, which were mostly located within the DMN. Reduced hippocampal RS FC with regions of the DMN was strongly correlated with higher T2 lesion volume, longer disease duration, and the severity of depression and disability. In patients with cognitively preserved MS, brain focal WM lesions are related to the functional integration of the hippocampus to other brain regions of the DMN, suggesting a disconnection syndrome. Such a disruption of hippocampal RS FC is likely to contribute to the occurrence of depression and to clinical disability.

APOE-ε4 Allele Altered the Rest-Stimulus Interactions in Healthy Middle-Aged Adults

The apolipoprotein E-ε4 allele is a well-known genetic risk factor for late-onset Alzheimer’s disease, which also impacts the cognitive functions and brain network connectivity in healthy middle-aged adults without dementia. Previous studies mainly focused on the effects of apolipoprotein E-ε4 allele on single index using task or resting-state fMRI. However, how these evoked and spontaneous BOLD indices interact with each other remains largely unknown. Therefore, we evaluated the ‘rest-stimulus interaction’ between working-memory activation and resting-state connectivity in middle-aged apolipoprotein E-ε4 carriers (n=9) and non-carriers (n=8). Four n-back task scans (n = 0, 1, 2, 3) and one resting-state scan were acquired at a 3T clinical MRI scanner. The working-memory beta maps of low-, moderate-, and high-memory loads and resting-state connectivity maps of default mode, executive control, and hippocampal networks were derived and compared between groups. Apolipoprotein E-ε4 carriers presented declined working-memory activation in the high-memory load across whole brain regions and reduced hippocampal connectivity compared with non-carriers. In addition, disrupted rest-stimulus interactions were found in the right anterior insula and bilateral parahippocampal regions for middle-aged adults with apolipoprotein E-ε4 allele. The rest-stimulus interaction improved the detectability of network integrity changes in apolipoprotein E-ε4 carriers, demonstrating the disrupted intrinsic connectivity within the executive-functional regions and the modulated memory-encoding capability within hippocampus-related regions.

Current versus lifetime depression, APOE variation, and their interaction on cognitive performance in younger and older adults

OBJECTIVE

An interaction effect of depressive symptoms and APOE e4 allele status on cognitive decline has been shown in old age: e4 allele carriers with more depressive symptoms have faster cognitive decline than those with either depression or the e4 allele. We test this interaction effect on four cognitive domains, using a clinical depression measure comparing current versus lifetime depression.

METHODS

14,379 individuals aged 18 to 59 years, and 3944 individuals aged 60 to 94 years from the Generation Scotland: Scottish Family Health Study participated. Linear-mixed models-accounting for participant relatedness and demographic and health indices-tested for effects of depression and APOE on cognitive abilities.

RESULTS

There was no interaction between depression and APOE on cognition (p > .05). Current depression was associated with poorer speed (in both groups) and memory (18- to 59-year-olds); differences ranged from 0.01 to 0.03 standard deviation [SD]. For lifetime depression, cognitive performance was lower for digit symbol in younger adults, but higher for vocabulary in both younger (0.03 SD) and older (0.05 SD) adults. A negative effect of the APOE e4 allele on speed and memory was found in the group 60 years and older (effect sizes of 0.04 SD).

CONCLUSIONS

The absence of a depression by APOE interaction on cognitive abilities suggests that these synergistic effects only operate at the level of cognitive decline. This implies that it is those biological pathways especially affected by aging that become compromised further by the combined presence of depression and APOE e4 in an individual.

Altered functional connectivity networks of hippocampal subregions in remitted late-onset depression: a longitudinal resting-state study

The regional specificity of hippocampal abnormalities in late-life depression (LLD) has been demonstrated in previous studies. In this study, we sought to examine the functional connectivity (FC) patterns of hippocampal subregions in remitted late-onset depression (rLOD), a special subtype of LLD. Fourteen rLOD patients and 18 healthy controls underwent clinical and cognitive evaluations as well as resting-state functional magnetic resonance imaging scans at baseline and at ∼21 months of follow-up. Each hippocampus was divided into three parts, the cornu ammonis (CA), the dentate gyrus, and the subicular complex, and then six seed-based hippocampal subregional networks were established. Longitudinal changes of the six networks over time were directly compared between the rLOD and control groups. From baseline to follow-up, the rLOD group showed a greater decline in connectivity of the left CA to the bilateral posterior cingulate cortex/precuneus (PCC/PCUN), but showed increased connectivity of the right hippocampal subregional networks with the frontal cortex (bilateral medial prefrontal cortex/anterior cingulate cortex and supplementary motor area). Further correlative analyses revealed that the longitudinal changes in FC between the left CA and PCC/PCUN were positively correlated with longitudinal changes in the Symbol Digit Modalities Test (r = 0.624, P = 0.017) and the Digit Span Test (r = 0.545, P = 0.044) scores in the rLOD group. These results may provide insights into the neurobiological mechanism underlying the cognitive dysfunction in rLOD patients.

Is Dysregulation of the HPA-Axis a Core Pathophysiology Mediating Co-Morbid Depression in Neurodegenerative Diseases?

There is increasing evidence of prodromal manifestation of neuropsychiatric symptoms in a variety of neurodegenerative diseases such as Parkinson's disease (PD) and Huntington's disease (HD). These affective symptoms may be observed many years before the core diagnostic symptoms of the neurological condition. It is becoming more apparent that depression is a significant modifying factor of the trajectory of disease progression and even treatment outcomes. It is therefore crucial that we understand the potential pathophysiologies related to the primary condition, which could contribute to the development of depression. The hypothalamic-pituitary-adrenal (HPA)-axis is a key neuroendocrine signaling system involved in physiological homeostasis and stress response. Disturbances of this system lead to severe hormonal imbalances, and the majority of such patients also present with behavioral deficits and/or mood disorders. Dysregulation of the HPA-axis is also strongly implicated in the pathology of major depressive disorder. Consistent with this, antidepressant drugs, such as the selective serotonin reuptake inhibitors have been shown to alter HPA-axis activity. In this review, we will summarize the current state of knowledge regarding HPA-axis pathology in Alzheimer's, PD and HD, differentiating between prodromal and later stages of disease progression when evidence is available. Both clinical and preclinical evidence will be examined, but we highlight animal model studies as being particularly useful for uncovering novel mechanisms of pathology related to co-morbid mood disorders. Finally, we purpose utilizing the preclinical evidence to better inform prospective, intervention studies.

Association between altered resting-state cortico-cerebellar functional connectivity networks and mood/cognition dysfunction in late-onset depression

The objective of the study is to investigate the relationship between altered resting-state cortico-cerebellar functional connectivity (FC) and depression as well as cognitive impairment in late-onset depression (LOD). A total of 32 LOD and 39 well-matched normal controls (NCs) were recruited and underwent resting-state functional MRI (R-fMRI) scans. Seed-based correlation analysis was performed to explore the cortico-cerebellar FC. Hamilton Depression Rating Scale (HAMD) and mini-mental state examination (MMSE) were used to evaluate the depressive severity and cognitive impairment, respectively. A set of neuropsychological measurements was also applied to evaluate the detailed cognitions. Spearman correlations were applied to examine the depressive and cognitive association of these altered cortico-cerebellar networks. Compared with the NCs, LOD patients showed increased FC between the cerebellum and the right ventromedial frontal cortex (vmPFC), supplementary motor area (SMA), middle temporal gyrus (MTG), bilateral supramarginal gyrus (SMG), and anterior cingulated cortex (ACC). However, reduced cerebellar FC was observed in bilateral cerebellum, posterior cingulated cortex (PCC) and left dorsolateral prefrontal cortex (dlPFC). Moreover, the cerebellar FC with the vmPFC and ACC was positively correlated with HAMD score, whereas the cerebellar FC with the dlPFC and PCC was positively correlated with MMSE score in LOD patients. The cortico-cerebellar disconnections might underlie the pathogenesis of LOD. While depression mainly relates to the excessive cerebellar FC with the vmPFC and ACC, cognitive decline is primarily associated with the uncoupling of the cerebellar FC with the dlPFC and PCC.