Low left amygdala volume is associated with a longer duration of unipolar depression

Brain-based Sex Differences in Depression: A Systematic Review of Neuroimaging Studies

Major depressive disorder (MDD) is a common psychiatric illness with a wide range of symptoms such as mood decline, loss of interest, and feelings of guilt and worthlessness. Women develop depression more often than men, and the diagnostic criteria for depression mainly rely on female patients' symptoms. By contrast, male depression usually manifests as anger attacks, aggression, substance use, and risk-taking behaviors. Various studies have focused on the neuroimaging findings in psychiatric disorders for a better understanding of their underlying mechanisms. With this review, we aimed to summarize the existing literature on the neuroimaging findings in depression, separated by male and female subjects. A search was conducted on PubMed and Scopus for magnetic resonance imaging (MRI), functional MRI (fMRI), and diffusion tensor imaging (DTI) studies of depression. After screening the search results, 15 MRI, 12 fMRI, and 4 DTI studies were included. Sex differences were mainly reflected in the following regions: 1) total brain, hippocampus, amygdala, habenula, anterior cingulate cortex, and corpus callosum volumes, 2) frontal and temporal gyri functions, along with functions of the caudate nucleus and prefrontal cortex, and 3) frontal fasciculi and frontal projections of corpus callosum microstructural alterations. Our review faces limitations such as small sample sizes and heterogeneity in populations and modalities. But in conclusion, it reflects the possible roles of sex-based hormonal and social factors in the depression pathophysiology.

Serum Levels of S100B Protein and Myelin Basic Protein as a Potential Biomarkers of Recurrent Depressive Disorders

Nowadays, nervous tissue damage proteins in serum are considered promising drug targets and biomarkers of Mood Disorders. In a cross-sectional naturalistic study, the S100B, MBP and GFAP levels in the blood serum were compared between two diagnostic groups (patients with Depressive Episode (DE, n = 28) and patients with Recurrent Depressive Disorder (RDD, n = 21)), and healthy controls (n = 25). The diagnostic value of serum markers was assessed by ROC analysis. In the DE group, we did not find changed levels of S100B, MBP and GFAP compared with controls. In the RDD group, we found decreased S100B level (p = 0.011) and increased MBP level (p = 0.015) in comparison to those in healthy controls. Provided ROC analysis indicates that MBP contributes to the development of a DE (AUC = 0.676; 95%Cl 0.525-0.826; p = 0.028), and S100B and MBP have a significant effect on the development of RDD (AUC = 0.732; 95%Cl 0.560-0.903; p = 0.013 and AUC = 0.712; 95%Cl 0.557-0.867; p = 0.015, correspondingly). The study of serum markers of nervous tissue damage in patients with a current DE indicates signs of disintegration of structural and functional relationships, dysfunction of gliotransmission, and impaired secretion of neurospecific proteins. Modified functions of astrocytes and oligodendrocytes are implicated in the pathophysiology of RDD.

Amygdala substructure volumes and serotonin transporter in first-episode, drug- naïve major depressive disorder: A pilot study

INTRODUCTION

Amygdala and serotonergic system abnormalities have been documented in major depressive disorder (MDD). However, most studies have been conducted on recurrent MDD, and only a few have assessed their interaction. This study aimed to concurrently examine both the amygdala and serotonergic systems and their clinical relevance in first-episode, drug-naïve MDD.

METHODS

This study included 27 patients with first-episode, drug-naïve MDD and 27 age- and gender-matched healthy controls (HCs). The amygdala substructure volumes were performed with Freesurfer from a 1.5 T magnetic resonance image. Serotonin transporter (SERT) availability was detected by single-photon emission computed tomography with ¹²³I-ADAM. The Benjamini-Hochberg method was applied to adjust for multiple comparisons.

RESULTS

No significant difference was found in the amygdala substructure volume and SERT availability between the two groups, respectively. Within MDD patients, the right medial, cortical nucleus, and centromedial volumes were positively associated with caudate SERT availability, respectively. Moreover, the right lateral nucleus volume in the amygdala was positively correlated with depression severity. However, these significances did not survive correction for multiple testing.

CONCLUSIONS

There were no significant abnormalities in the amygdala substructure volumes and SERT availability in patients with first-episode, drug-naïve MDD. We did not observe an association between amygdala substructure volume and serotonergic dysregulation and their correlations with depression severity in patients with MDD. A larger sample size is warranted to elucidate the actual correlation.

Differences in gray matter volumes of subcortical nuclei between major depressive disorder with and without persistent depressive disorder

OBJECTIVE

This study aimed to compare the differences in gray matter volumes (GMVs) of subcortical nuclei between major depressive disorder (MDD) patients with and without persistent depressive disorder (PDD) at long-term follow-up.

METHODS

114 and 94 subjects with MDD, including 48 and 41 with comorbid PDD, were enrolled to undergo high-resolution T1-weighted imaging at first (FIP) and second (three years later, SIP) investigation points, respectively. FreeSurfer was used to extract the GMVs of seven subcortical nuclei, and Generalized Estimating Equation models were employed to estimate the differences in GMVs of subcortical nuclei between the two subgroups.

RESULTS

The PDD subgroup had a significantly greater depressive severity and a higher percentage of patients undergoing pharmacotherapy at the FIP as compared with the non-PDD subgroup. These differences became insignificant at the SIP. The PDD subgroup had a significantly (p < 0.003) smaller GMV in the right putamen at the SIP and in the right nucleus accumbens (NAc) at the FIP and SIP as compared with the non-PDD subgroup. After controlling for clinical variables, PDD was independently associated with smaller GMVs in the right putamen and NAc.

LIMITATIONS

Imaging was not performed at baseline and pharmacotherapy was not controlled at the FIP and SIP.

CONCLUSIONS

MDD with PDD was associated with smaller GMVs in the right putamen and NAc as compared with MDD without PDD. Whether the two regions are biomarkers related to a poor prognosis and the chronicity of depression requires further study.

Atrophy in subcortical gray matter in adult patients with moyamoya disease

BACKGROUND

Acute cerebrovascular accidents, long-term hypoperfusion, and/or remote neuronal degeneration may lead to structural alterations in patients with moyamoya disease (MMD). This study sought to comprehensively investigate the distribution characteristics of subcortical gray matter volume and their correlations with angiographic changes in the intracranial artery in patients with MMD.

METHOD

One hundred forty-two patients with MMD and 142 age- and sex-matched healthy controls underwent 3-dimensional high-resolution structural magnetic resonance imaging. Volumes of subcortical gray matter and subregions of the hippocampus and amygdala were calculated, and the degree of stenosis/occlusion of intracranial arteries in patients with MMD was evaluated on MR angiography.

RESULTS

Volume reductions in the thalamus, caudate, putamen, hippocampus, amygdala, pallidum, and nucleus accumbens were found in patients with MMD. Hippocampal subfields and amygdala subnuclei in patients with MMD showed distinct vulnerability, and morphological alterations in specific subregions were more obvious than in the whole hippocampus/amygdala. Volume loss in several subcortical areas was related to disease duration and intracranial arterial changes.

CONCLUSIONS

Our findings revealed structural alteration patterns of subcortical gray matter in MMD. The specific atrophy in subregions of the hippocampus and the amygdala suggested potential cognitive and affective impairments in MMD, which warrants further investigation. Chronic cerebral hemodynamic alterations in MMD may play a pivotal role in morphological changes in subcortical areas.

Structural covariance network of the hippocampus-amygdala complex in medication-naïve patients with first-episode major depressive disorder

Background

The hippocampus and amygdala are densely interconnected structures that work together in multiple affective and cognitive processes that are important to the etiology of major depressive disorder (MDD). Each of these structures consists of several heterogeneous subfields. We aim to explore the topologic properties of the volume-based intrinsic network within the hippocampus-amygdala complex in medication-naïve patients with first-episode MDD.

Methods

High-resolution T1-weighted magnetic resonance imaging scans were acquired from 123 first-episode, medication-naïve, and noncomorbid MDD patients and 81 age-, sex-, and education level-matched healthy control participants (HCs). The structural covariance network (SCN) was constructed for each group using the volumes of the hippocampal subfields and amygdala subregions; the weights of the edges were defined by the partial correlation coefficients between each pair of subfields/subregions, controlled for age, sex, education level, and intracranial volume. The global and nodal graph metrics were calculated and compared between groups.

Results

Compared with HCs, the SCN within the hippocampus-amygdala complex in patients with MDD showed a shortened mean characteristic path length, reduced modularity, and reduced small-worldness index. At the nodal level, the left hippocampal tail showed increased measures of centrality, segregation, and integration, while nodes in the left amygdala showed decreased measures of centrality, segregation, and integration in patients with MDD compared with HCs.

Conclusion

Our results provide the first evidence of atypical topologic characteristics within the hippocampus-amygdala complex in patients with MDD using structure network analysis. It provides more delineate mechanism of those two structures that underlying neuropathologic process in MDD.

Regional gray matter volume mediates the relationship between neuroticism and depressed emotion

The underlying psychological mechanism of the effect of neuroticism on depressed emotion has been widely studied. However, the neural mechanism of this relationship remains unclear. Therefore, the present study aimed to apply voxel-based morphometry (VBM) to explore the neural mechanism of the relationship between depressed emotion and neuroticism in healthy and young participants through longitudinal tracking research. The behavioral results showed that neuroticism was positively related to depressed emotion at T1 and T2 (6 months later). The VBM analysis revealed that neuroticism positively associated with the gray matter volume (GMV) in the dorsal medial prefrontal cortex (dmPFC). Mediation analysis was conducted to investigate the neural basis of the association between depressed emotion and neuroticism. The mediation result revealed that GMV of the dmPFC partially mediates the relationship between neuroticism and depressed emotion at T1 but not T2. Together, these findings suggest that the gray matter volume of dmPFC could may affect the relationship between depressed emotion and neuroticism.

Brain morphometry and connectivity differs between adolescent- and adult-onset major depressive disorder

BACKGROUND

Early-onset (EO) major depressive disorder (MDD) patients experience more depressive episodes and an increased risk of relapse. Thus, on a neurobiological level, adult EO patients might display brain structure and function different from adult-onset (AO) patients.

METHODS

A total of 103 patients (66 females) underwent magnetic resonance imaging. Structural measures of gray matter volume (GMV) and functional connectivity networks during resting state were compared between EO (≤19 years) and AO groups. Four residual major depression symptoms, mood, anxiety, insomnia, and somatic symptoms, were correlated with GMV between groups.

RESULTS

We found comparatively increased GMV in the EO group, namely the medial prefrontal and insular cortex, as well as the anterior hippocampus. Functional networks in EO patients showed a comparatively weaker synchronization of the left hippocampus with the adjacent amygdala, and a stronger integration with nodes in the contralateral prefrontal cortex and supramarginal gyrus. Volumetric analysis of depression symptoms associated the caudate nuclei with symptoms of insomnia, and persisting mood symptoms with the right amygdala, while finding no significant clusters for somatic and anxiety symptoms.

CONCLUSIONS

The study highlights the important role of the hippocampus and the prefrontal cortex in EO patients as part of emotion-regulation networks. Results in EO patients demonstrated subcortical volume changes irrespective of sleep and mood symptom recovery, which substantiates adolescence as a pivotal developmental phase for MDD. Longitudinal studies are needed to differentiate neural recovery trajectories while accounting for age of onset.

Volume of Amygdala Subregions and Plasma Levels of Brain-Derived Neurotrophic Factor and Cortisol in Patients with s/s Genotype of Serotonin Transporter Gene Polymorphism of First-Episode and Drug-Naive Major Depressive Disorder: An Exploratory Study

The amygdala is a prominent region of the brain that plays a critical role in the pathophysiology of major depressive disorder (MDD). The amygdala is formed from a collection of interconnected substructures (nuclei) that relay signals from multiple brain areas, which suggests that the amygdala has different functions depending on its subregion. There are two main alleles of serotonin transporter gene polymorphism (5-HTTLPR): a 44-bp insertion (l-allele) or deletion (s-allele). The transcriptional activity of the l-allele of the gene is twice that of the s-allele. The present study aimed to investigate the association between the volume of the whole amygdala and subregions of the amygdala in 25 first-episode and drug-naive patients with MDD and 46 healthy controls (HCs) with the s/s genotype of 5-HTTLPR and plasma levels of brain-derived neurotrophic factor (BDNF) or cortisol. No significant difference was observed in the amygdala total and subregion volumes between the HC and MDD groups. No significant difference was found in the plasma levels of BDNF and cortisol between the two groups. In addition, no correlations were found between the total and subregion amygdala volume and plasma levels of cortisol or BDNF.

A Longitudinal Study of Medial Temporal Lobe Volumes in Graves Disease

CONTEXT

Neuropsychiatric symptoms are common features of Graves disease (GD) in hyperthyroidism and after treatment. The mechanism behind these symptoms is unknown, but reduced hippocampal volumes have been observed in association with increased thyroid hormone levels.

OBJECTIVE

This work aimed at investigating GD influence on regional medial temporal lobe (MTL) volumes.

METHODS

Sixty-two women with newly diagnosed GD underwent assessment including magnetic resonance (MR) imaging in hyperthyroidism and 48 of them were followed up after a mean of 16.4 ± 4.2 SD months of treatment. Matched thyroid-healthy controls were also assessed twice at a 15-month interval. MR images were automatically segmented using multiatlas propagation with enhanced registration. Regional medial temporal lobe (MTL) volumes for amygdalae and hippocampi were compared with clinical data and data from symptom questionnaires and neuropsychological tests.

RESULTS

Patients had smaller MTL regions than controls at inclusion. At follow-up, all 4 MTL regions had increased volumes and only the volume of the left amygdala remained reduced compared to controls. There were significant correlations between the level of thyrotropin receptor antibodies (TRAb) and MTL volumes at inclusion and also between the longitudinal difference in the levels of free 3,5,3'-triiodothyronine and TRAb and the difference in MTL volumes. There were no significant correlations between symptoms or test scores and any of the 4 MTL volumes.

CONCLUSION

Dynamic alterations in the amygdalae and hippocampi in GD reflect a previously unknown level of brain involvement both in the hyperthyroid state of the condition and after treatment. The clinical significance, as well as the mechanisms behind these novel findings, warrant further study of the neurological consequences of GD.

Volume of Amygdala Subregions and Clinical Manifestations in Patients With First-Episode, Drug-Naïve Major Depression

We examined amygdala subregion volumes in patients with a first episode of major depression (MD) and in healthy subjects. Covariate-adjusted linear regression was performed to compare the MD and healthy groups, and adjustments for age, gender, and total estimated intracranial volume showed no differences in amygdala subregion volumes between the healthy and MD groups. Within the MD group, we examined the association between amygdala subregion volume and the 17-item Hamilton Rating Scale for Depression (HAMD) score and the HAMD subscale score, and found no association in the left amygdala. In the right amygdala, however, there was an inverse linear association between the HAMD total and the HAMD core and lateral nucleus and anterior-amygdaloid-regions. Furthermore, an inverse linear association was seen between the HAMD psychic and the lateral nucleus, anterior-amygdaloid-regions, transition, and whole amygdala. The findings of this study suggest that the severity of MD and some symptoms of MD are associated with right amygdala volume. There have been few reports on the relationship between MD and amygdala subregional volume, and further research is needed to accumulate more data for further validation.

Volumetric alterations in subregions of the amygdala in adults with major depressive disorder

BACKGROUND

Although major depressive disorder (MDD) has been associated with volumetric abnormalities in the amygdala, studies investigating the association between structural alterations of the amygdala and depression have yielded varying results. Since the amygdala comprises several subregions, it is difficult to detect subtle regional changes by measuring the total amygdala volume. This study aimed to examine the volume in each amygdala subregion in adults with and without a diagnosis of MDD.

METHODS

A total of 147 participants with a current history of major depression and 144 healthy participants ranging in age from 19 to 64 years underwent 3T magnetic resonance imaging scanning. Automatic segmentation of the nine nuclei of the amygdala was performed using FreeSurfer. One-way analysis of covariance, with individual volumes as dependent variables, and age, sex, and total intracranial volume as covariates, was performed to analyze volume differences.

RESULTS

Patients with MDD had significantly lower volumes of the entire amygdala and subregions, including the lateral nucleus and anterior amygdaloid area, than healthy volunteers (HCs). There were no significant associations between subregion volumes and antidepressant use, illness duration, or depression severity.

LIMITATIONS

Our cross-sectional design cannot provide a causal relationship between the volume change in the amygdala subregion and the risk of MDD.

CONCLUSION

Our findings suggest that specific amygdala subregions are more susceptible to volumetric alterations in patients with MDD than in HCs. These findings may advance our understanding of the neuroanatomic basis on MDD.

Left amygdala volume and brain tissue pulsatility are associated with neuroticism: an MRI and ultrasound study

Brain changes associated with the personality trait of neuroticism have been partly elucidated. While subcortical brain volume changes, especially a larger amygdala, appear consistent in high neuroticism, functional changes, such as cerebral blood flow (CBF) differences, have shown conflicting results, possibly because of the limitations in methods of CBF measurement. In our study, we investigated changes in amygdala volume and CBF-related function associated with neuroticism in healthy and depressed subjects using both conventional magnetic resonance imaging (MRI) measures of brain volume and the innovative technique of ultrasound Tissue Pulsatility Imaging (TPI), which has a high level of detection in measuring brain tissue pulsatility (BTP). Middle-aged females with depression (n = 25) and without depression (n = 25) underwent clinical examination, magnetic resonance imaging (MRI) and ultrasound assessment (TPI). Neuroticism was positively associated with left amygdala volume and mean BTP in individuals without depression, in both simple and multiple regressions that included potential confounding factors such as age and body mass index. No association was found in the depressed group. We confirmed the role of the left amygdala in the brain physiology of neuroticism in nondepressed individuals. Moreover, we identified a novel mechanism associated with high neuroticism, namely BTP, that may reflect greater CBF and account for the increased risk of cerebrovascular disease in individuals with high neuroticism. Because neuroticism is considered a risk factor for depression, our paper provides potential objective biomarkers for the identification of subjects at risk for depression.

Psychopathological Syndromes Across Affective and Psychotic Disorders Correlate With Gray Matter Volumes

INTRODUCTION

More than a century of research on the neurobiological underpinnings of major psychiatric disorders (major depressive disorder [MDD], bipolar disorder [BD], schizophrenia [SZ], and schizoaffective disorder [SZA]) has been unable to identify diagnostic markers. An alternative approach is to study dimensional psychopathological syndromes that cut across categorical diagnoses. The aim of the current study was to identify gray matter volume (GMV) correlates of transdiagnostic symptom dimensions.

METHODS

We tested the association of 5 psychopathological factors with GMV using multiple regression models in a sample of N = 1069 patients meeting Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) criteria for MDD (n = 818), BD (n = 132), and SZ/SZA (n = 119). T1-weighted brain images were acquired with 3-Tesla magnetic resonance imaging and preprocessed with CAT12. Interactions analyses (diagnosis × psychopathological factor) were performed to test whether local GMV associations were driven by DSM-IV diagnosis. We further tested syndrome specific regions of interest (ROIs).

RESULTS

Whole brain analysis showed a significant negative association of the positive formal thought disorder factor with GMV in the right middle frontal gyrus, the paranoid-hallucinatory syndrome in the right fusiform, and the left middle frontal gyri. ROI analyses further showed additional negative associations, including the negative syndrome with bilateral frontal opercula, positive formal thought disorder with the left amygdala-hippocampus complex, and the paranoid-hallucinatory syndrome with the left angular gyrus. None of the GMV associations interacted with DSM-IV diagnosis.

CONCLUSIONS

We found associations between psychopathological syndromes and regional GMV independent of diagnosis. Our findings open a new avenue for neurobiological research across disorders, using syndrome-based approaches rather than categorical diagnoses.

Common and Specific Alterations of Amygdala Subregions in Major Depressive Disorder With and Without Anxiety: A Combined Structural and Resting-State Functional MRI Study

Anxious major depressive disorder is a common subtype of major depressive disorder; however, its unique neural mechanism is not well-understood currently. Using multimodal MRI data, this study examined common and specific alterations of amygdala subregions between patients with and without anxiety. No alterations were observed in the gray matter volume or intra-region functional integration in either patient group. Compared with the controls, both patient groups showed decreased functional connectivity between the left superficial amygdala and the left putamen, and between the right superficial amygdala and the bilateral anterior cingulate cortex and medial orbitofrontal cortex, while only patients with anxiety exhibited decreased activity in the bilateral laterobasal and superficial amygdala. Moreover, the decreased activity correlated negatively with the Hamilton depression scale scores in the patients with anxiety. These findings provided insights into the pathophysiologic processes of anxious major depressive disorder and may help to develop new and effective treatment programs.

Ventricular volume, white matter alterations and outcome of major depression and their relationship to endocrine parameters - A pilot study

OBJECTIVES

Brain morphology and its relation to endocrine parameters were examined, in order to determine the link of these parameters to treatment outcome to psychopharmacological treatment in depressed patients.

METHODS

We examined the potentially predictive value of Magnetic Resonance Imaging (MRI) parameters related to mineralocorticoid receptor (MR) function on the treatment outcome of depression. 16 inpatients with a major depressive episode (MDE) were studied at baseline and 14 of them approximately six weeks later. Physiological biomarkers and 3-T-structural MRI based volume measures, using FreeSurfer 6.0 software, were determined.

RESULTS

Non-responders (<50% reduction of HAMD-21; n = 6) had a significantly smaller volume of the right anterior cingulate cortex, a significantly larger ventricle to brain ratio (VBR) and third ventricle volume, and smaller volumes of the central and central-anterior corpus callosum (CC) in comparison to responders (n = 7; all p ≤ 0.05). Correlational analysis (Spearman) demonstrated that larger ventricle volume was correlated to a worse treatment outcome, higher body mass index (BMI) and smaller CC segment volume, whereas the total CC volume was negatively correlated to the saliva aldosterone/cortisol concentration ratio (AC-ratio).

CONCLUSION

Large ventricular volume may be a predictive marker for worse treatment response to standard antidepressant treatment, potentially via compression of white matter structures. A mediating role of the previously identified markers BMI and the AC-ratio, is suggested.

Plasma Neuronal and Glial Markers and Anterior Cingulate Metabolite Levels in Major Depressive Disorder: A Pilot Study

INTRODUCTION

Neuroglial functions may be deteriorated in major depressive disorder (MDD).

OBJECTIVE

To evaluate the markers of glial and neuronal cell turnover and to explore their associations with brain metabolites.

METHODS

In 10 participants with MDD and 10 healthy controls (HC) we investigated neuronal and glial plasma markers (the neuron-specific enolase, NSE; and S100beta, S100B) and brain metabolites (N-acetyl aspartate, NAA; total choline, Cho; and total creatine, Cr). Blood was collected for NSE and S100B. NAA, Cho, and Cr metabolite levels were measured in the anterior cingulate cortex (ACC) with proton magnetic resonance spectroscopy (1H-MRS) at 3T.

RESULTS

NSE and S100B levels were significantly higher in MDD subjects than in HC. The Cr level was significantly higher in MDD subjects than in HC, but the NAA and Cho levels did not differ between groups. NAA/Cr and Cho/Cr ratios were significantly lower in patients with MDD versus HC. S100B was negatively correlated with the Cho levels.

CONCLUSIONS

These results provide supporting evidence of neuronal and glial distress in MDD. Neuronal viability appears decreased, whereas glial regenerative activity and energy metabolism in the ACC increase in acute major depressive episode. Since low concentrations of S100B have neuroplastic effects, these changes may indicate a possible compensatory mechanism.

Longitudinal effects of rTMS on neuroplasticity in chronic treatment-resistant depression

Major depressive disorder (MDD) is amongst the most prevalent of psychiatric disorders. Unfortunately, a third of patients will not respond to conventional treatments and suffer from treatment-resistant depression (TRD). Repetitive transcranial magnetic stimulation (rTMS) has been proven effective in treating TRD. The research suggests that rTMS acts via neuroplastic effects on the brain, which can be measured by changes in hippocampal and amygdala volume as well as cortical thickness. This sham-controlled study investigates longitudinal effects of rTMS on the volumes of the hippocampus and amygdala and cortical thickness in patients with chronic TRD. 31 patients received 20 sessions of high-frequency rTMS (N = 15) or sham treatment (N = 16) over the left dorsolateral prefrontal cortex during 4 consecutive weeks. Using structural magnetic resonance imaging, we investigated longitudinal treatment effects on hippocampus and amygdala volume as well as thickness of the paralimbic cortex. We found no clinical differences between the active and sham rTMS group. Longitudinal changes in hippocampal and amygdala volume did not differ significantly, although males showed a significant decrease in left amygdala volume, irrespective of treatment group. Changes in cortical thickness of the paralimbic cortex differed significantly between the active and sham groups. Most notably, the increase in cortical thickness of the isthmus of the left cingulate gyrus was greater in the active as compared to the sham rTMS group. Our data suggest that rTMS can induce neuroplastic changes, particularly in cortical thickness, independent of treatment response. We also found longitudinal changes in amygdala volume in males. For clinical effects to follow these neuroplastic effects, more intensive rTMS treatment might be needed in chronically depressed patients.Trial registration number: ISRCTN 15535800, registered on 29-06-2017.

Hippocampal and Amygdalar Volume Changes in Major Depressive Disorder: A Targeted Review and Focus on Stress

Medial temporal lobe structures have long been implicated in the pathogenesis of major depressive disorder. Although findings of smaller hippocampal and amygdalar volumes are common, inconsistencies remain in the literature. In this targeted review, we examine recent and significant neuroimaging papers examining the volumes of these structures in major depressive disorder. A targeted PubMed/Google Scholar search was undertaken focusing on volumetric neuroimaging studies of the hippocampus and amygdala in major depressive disorder. Where possible, mean volumes and accompanying standard deviations were extracted allowing computation of Cohen’s d_s effect sizes. Although not a meta-analysis, this allows a broad comparison of volume changes across studies. Thirty-nine studies in total were assessed. Hippocampal substructures and amygdale substructures were investigated in 11 and 2 studies, respectively. The hippocampus was more consistently smaller than the amygdala across studies, which is reflected in the larger cumulative difference in volume found with the Cohen’s d_s calculations. The left and right hippocampi were, respectively, 92% and 91.3% of the volume found in controls, and the left and right amygdalae were, respectively, 94.8% and 92.6% of the volume of controls across all included studies. The role of stress in temporal lobe structure volume reduction in major depressive disorder is discussed.

Aberrant limbic brain structures in young individuals at risk for mental illness

AIM

Alterations in limbic structures may be present before the onset of serious mental illness, but whether subfield-specific limbic brain changes parallel stages in clinical risk is unknown. To address this gap, we compared the hippocampus, amygdala, and thalamus subfield-specific volumes in adolescents at various stages of risk for mental illness.

METHODS

MRI scans were obtained from 182 participants (aged 12-25 years) from the Canadian Psychiatric Risk and Outcome study. The sample comprised of four groups: asymptomatic youth at risk due to family history of mental illness (Stage 0, n = 32); youth with early symptoms of distress (Stage 1a, n = 41); youth with subthreshold psychotic symptoms (Stage 1b, n = 72); and healthy comparison participants with no family history of serious mental illness (n = 37). Analyses included between-group comparisons of brain measurements and correlational analyses that aimed to identify significant associations between neuroimaging and clinical measurements. A machine-learning technique examined the discriminative properties of the clinical staging model.

RESULTS

Subfield-specific limbic volume deficits were detected at every stage of risk for mental illness. A machine-learning classifier identified volume deficits within the body of the hippocampus, left amygdala nuclei, and medial-lateral nuclei of the thalamus that were most informative in differentiating between risk stages.

CONCLUSION

Aberrant subfield-specific changes within the limbic system may serve as biological evidence to support transdiagnostic clinical staging in mental illness. Differential patterns of volume deficits characterize those at risk for mental illness and may be indicative of a risk-stage progression.

Structural MRI at 7T reveals amygdala nuclei and hippocampal subfield volumetric association with Major Depressive Disorder symptom severity

Subcortical volumetric changes in major depressive disorder (MDD) have been purported to underlie depressive symptomology, however, the evidence to date remains inconsistent. Here, we investigated limbic volumes in MDD, utilizing high-resolution structural images to allow segmentation of the hippocampus and amygdala into their constituent substructures. Twenty-four MDD patients and twenty matched controls underwent structural MRI at 7T field strength. All participants completed the Montgomery-Asberg Depression Rating Scale (MADRS) to quantify depressive symptomology. For the MDD group, volumes of the amygdala right lateral nucleus (p = 0.05, r2 = 0.24), left cortical nucleus (p = 0.032, r2 = 0.35), left accessory basal nucleus (p = 0.04, r2 = 0.28) and bilateral corticoamygdaloid transition area (right hemisphere p = 0.032, r2 = 0.38, left hemisphere p = 0.032, r2 = 0.35) each displayed significant negative associations with MDD severity. The bilateral centrocortical (right hemisphere p = 0.032, r2 = 0.31, left hemisphere p = 0.032, r2 = 0.32) and right basolateral complexes (p = 0.05, r2 = 0.24) also displayed significant negative relationships with depressive symptoms. Using high-field strength MRI, we report the novel finding that MDD severity is consistently negatively associated with amygdala nuclei, linking volumetric reductions with worsening depressive symptoms.

Relationship between depressive symptom severity and amygdala volume in a large community-based sample

Amygdala is an affective processing center that regulates and assigns valence to different emotions and has been implicated in the pathophysiology of mood disorders. This population-based study employed a community sample of 1747 adults to examine relationships between amygdala volume and depressive symptom severity. Neuroimaging data from participants in the Dallas Heart Study were used. Magnetic resonance images of right, left, and total amygdala volume were used as response variables in multiple regressions. Predictor variables included Quick Inventory of Depressive Symptomatology Self-Report (QIDS-SR) scores, intracranial volume, age, gender, race/ethnicity, body mass index, self-reported alcohol use, years of education, and psychotropic medication use. In the overall sample, QIDS-SR scores were not significantly related to left, right or total amygdala volume. A significant QIDS-SR by age interaction was observed, thus a follow-up subgroup analysis was conducted in age groups 18-39, 40-59, and ≥ 960. A significant negative relationship was observed between QIDS-SR scores and right and total, but not left, amygdala volume in the 18-39 age group but not in other age groups. Significant relationship between QIDS-SR scores and amygdala volume in young adults suggests possible biological differences in depressive symptoms in people of this age group.

Longitudinal brain volume changes in major depressive disorder

Patients with major depressive disorder (MDD) exhibit gray matter volume (GMV) reductions in limbic regions. Clinical variables-such as the number of depressive episodes-seem to affect volume alterations. It is unclear whether the observed cross-sectional GMV abnormalities in MDD change over time, and whether there is a longitudinal relationship between GMV changes and the course of disorder. We investigated T1 structural MRI images of 54 healthy control (HC) and 37 MDD patients in a 3-Tesla-MRI with a follow-up interval of 3 years. The Cat12 toolbox was used to analyze longitudinal data (p < 0.05, FWE-corrected, whole-brain analysis; flexible factorial design). Interaction effects indicated increasing GMV in MDD in the bilateral amygdala, and decreasing GMV in the right thalamus between T1 and T2. Further analyses comparing patients with a mild course of disorder (MCD; 0-1 depressive episode during the follow-up) to patients with a severe course of disorder (SCD; > 1 depressive episode during the follow-up) revealed increasing amygdalar volume in MCD. Our study confirms structural alterations in limbic regions in MDD patients and an association between these impairments and the course of disorder. Thus, we assume that the reported volumetric alterations in the left amygdala (i.e. volumetric normalization) are reversible and apparently driven by the clinical phenotype. Hence, these results support the assumption that the severity and progression of disease influences amygdalar GMV changes in MDD or vice versa.