Abnormal long- and short-range functional connectivity in patients with first-episode drug-naïve melancholic and non-melancholic major depressive disorder

Disrupted interhemispheric functional and structural connectivity in patients with major depressive disorder

BACKGROUND

Major depressive disorder (MDD) is associated with disrupted interhemispheric cooperation. However, the relationship between structural and functional alterations in interhemispheric cooperation in patients with MDD remains unclear. We investigated the associations between voxel-mirrored homotopic connectivity (VMHC) and radial diffusivity (RD) within the corpus callosum (CC) and their links to depressive symptoms in patients with MDD.

METHODS

Sixty patients with MDD and 38 healthy controls (HCs) were assessed using resting-state functional MRI (rs-fMRI) and diffusion MRI (dMRI) to evaluate interhemispheric functional connectivity (VMHC) and structural integrity (RD) in the CC subregions. Group comparisons, correlation analyses, and mediation analyses were conducted to identify the significant differences, relationships, and indirect effects.

RESULTS

Patients with MDD showed significantly reduced VMHC in the bilateral postcentral gyrus and lingual gyrus and increased RD in the CC subregions CC3, CC4, and CC5, indicating impaired functional and structural connectivity. Lower VMHC in the lingual gyrus was negatively correlated with depressive severity, whereas increased RD in the CC4 and CC5 was positively correlated with depressive symptoms. Mediation analysis revealed that the VMHC in the lingual gyrus fully mediated the relationship between RD in CC5 and depressive symptoms, suggesting a pathway through which structural impairments may affect mood through abnormal functional connectivity.

LIMITATIONS

The cross-sectional design limits the assessment of changes over time, and focusing solely on interhemispheric connectivity may overlook other networks involved in MDD.

CONCLUSION

These findings provide preliminary evidence for disrupted interhemispheric coordination in MDD, with both functional and structural connectivity impairments linked to depressive symptoms. The mediating effect of the VMHC in the lingual gyrus highlights the potential role of interhemispheric connectivity in the pathophysiology of MDD. Our results provide an integrative perspective on the functional and microstructural organization of the brain in patients with MDD.

Abnormal regional brain activity in patients with first-episode medication-naïve depressive disorder: A longitudinal fNIRS study

The potential relationship between abnormal brain activity and clinical symptoms in patients with major depressive disorder (MDD) is important for auxiliary diagnosis and prediction of the curative effect of treatments for MDD. Before antidepressant treatment (T1), 4 weeks after treatment (T2), and 8 weeks after treatment (T3), 33 patients with first-episode medication-naïve MDD and 30 healthy controls (HCs) were examined using functional near-infrared spectroscopy (fNIRS) to evaluate the cerebral hemodynamic response in the frontal and temporal cortex during the Verbal Fluency Task (VFT). Compared with HCs, VFT scores and activation levels of the frontal pole, inferior frontal gyrus, and dorsolateral prefrontal cortex were significantly decreased in the first-episode medication-naïve depressive disorder patients (FMD). Compared with T2, the activation levels of the superior temporal gyrus and inferior central gyrus were increased at T3 in the FMD. The low activation pattern of the frontal pole, inferior frontal gyrus, and dorsolateral prefrontal cortex in the FMD during VFT is helpful for clinical diagnosis of MDD. The superior temporal gyrus and inferior central gyrus may be sensitive brain regions that reflect the clinical effect of MDD in patients.

Neurophysiological markers of disease severity and cognitive dysfunction in major depressive disorder: A TMS-EEG study

Background

Transcranial magnetic stimulation-electroencephalography (TMS-EEG) is a powerful technique to study the neuropathology and biomarkers of major depressive disorder (MDD). This study investigated cortical activity and its relationship with clinical symptoms and cognitive dysfunction in MDD patients by indexing TMS-EEG biomarkers in the dorsolateral prefrontal cortex (DLPFC).

Methods

133 patients with MDD and 76 healthy individuals participated in this study. Single-pulse TMS was performed on the left DLPFC to obtain TMS-evoked potential (TEP) indices. TMS-EEG waveforms and components were determined by global mean field amplitude. We used the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) to measure participants' cognitive function.

Results

Patients with MDD had a lower excitatory P180 index compared to healthy controls, and P180 amplitude was negatively correlated with the severity of depressive and anxiety symptoms in patients with MDD. In the MDD group, P30 amplitude was negatively associated with RBANS Visuospatial/ Constructional index and total score.

Conclusions

TMS-EEG findings suggest that abnormal cortical excitation and inhibition induced by TMS on the DLPFC are associated with the severity of clinical symptoms and cognitive dysfunction in patients with MDD. P180 and P30 have the potential to serve as neurophysiological biomarkers of clinical symptoms and cognitive dysfunction in MDD patients, respectively.

Altered functional-structural coupling may predict Parkinson's patient's depression

We aimed to elucidate the neurobiological basis of depression in Parkinson's disease and identify potential imaging markers for depression in patients with Parkinson's disease. We recruited 43 normal controls (NC), 46 depressed Parkinson's disease patients (DPD) and 56 non-depressed Parkinson's disease (NDPD). All participants underwent routine T2-weighted, T2Flair, and resting-state scans on the same 3.0 T magnetic resonance imaging (MRI) scanner at our hospital. Pre-processing includes calculating surface-based Regional Homogeneity (2DReHo) and cortical thickness. Then we defined the correlation coefficient between 2DReHo and cortical thickness as the functional-structural coupling index. Between-group comparisons were conducted on the Fisher's Z-transformed correlation coefficients. To identify specific regions of decoupling, the 2DReHo for each participant were divided by cortical thickness at each vertex, followed by threshold-free cluster enhancement (TFCE) multiple comparison correction. Binary logistic regression analysis was performed with DPD as the dependent variable, and significantly altered indicators as the independent variables. Receiver operating characteristic curves were constructed to compare the diagnostic performance of individual predictors and combinations using R and MedCalc software. DPD patients exhibited a significantly lower whole-brain functional-structural coupling index than NDPD patients and NC. Abnormal functional-structural coupling was primarily observed in the left inferior parietal lobule and right primary and early visual cortices in DPD patients. Receiver operating characteristic analysis revealed that the combination of cortical functional-structural coupling, surface-based ReHo, and thickness had the best diagnostic performance, achieving a sensitivity of 65% and specificity of 77.7%. This is the first study to explore the relationship between functional and structural changes in DPD patients and evaluate the diagnostic performance of these altered correlations to predict depression in Parkinson's disease patients. We posit that these changes in functional-structural relationships may serve as imaging biomarkers for depression in Parkinson's disease patients, potentially aiding in the classification and diagnosis of Parkinson's disease. Additionally, our findings provide functional and structural imaging evidence for exploring the neurobiological basis of depression in Parkinson's disease.

Increased brain nucleus accumbens functional connectivity in melancholic depression

BACKGROUND

Melancholic depression, marked by typical symptoms of anhedonia, is regarded as a homogeneous subtype of major depressive disorder (MDD). However, little attention was paid to underlying mechanisms of melancholic depression. This study aims to examine functional connectivity of the reward circuit associated with anhedonia symptoms in melancholic depression.

METHODS

Fifty-nine patients with first-episode drug- naive MDD, including 31 melancholic patients and 28 non-melancholic patients, were recruited and underwent resting-state functional magnetic resonance imaging (rs-fMRI). Thirty-two healthy volunteers were recruited as controls. Bilateral nucleus accumbens (NAc) were selected as seed points to form functional NAc network. Then support vector machine (SVM) was used to distinguish melancholic patients from non-melancholic patients.

RESULTS

Relative to non-melancholic patients, melancholic patients displayed increased functional connectivity (FC) between bilateral NAc and right middle frontal gyrus (MFG) and between right NAc and left cerebellum lobule VIII. Compared to healthy controls, melancholic patients showed increased FC between right NAc and right lingual gyrus and between left NAc and left postcentral gyrus; non-melancholic patients had increased FC between bilateral NAc and right lingual gyrus. No significant correlations were observed between altered FC and clinical variables in melancholic patients. SVM results showed that FC between left NAc and right MFG could accurately distinguish melancholic patients from non-melancholic patients.

CONCLUSION

Melancholic depression exhibited different patterns of functional connectivity of the reward circuit relative to non-melancholic patients. This study highlights the significance of the reward circuit in the neuropathology of melancholic depression.

Functional connectivity of the left inferior parietal lobule mediates the impact of anxiety and depression symptoms on sleep quality in healthy adults

Individuals with anxiety and depression symptoms are vulnerable to sleep disturbances. The current study aimed to explore the shared neuro-mechanisms underlying the effect of anxiety and depression symptoms on sleep quality. We recruited a cohort of 92 healthy adults who underwent functional magnetic resonance imaging scanning. We measured anxiety and depression symptoms using the Zung Self-rating Anxiety/Depression Scales and sleep quality using the Pittsburgh Sleep Quality Index. Independent component analysis was used to explore the functional connectivity (FC) of brain networks. Whole-brain linear regression analysis showed that poor sleep quality was associated with increased FC in the left inferior parietal lobule (IPL) within the anterior default mode network. Next, we extracted the covariance of anxiety and depression symptoms using principal component analysis to represent participants' emotional features. Mediation analysis revealed that the intra-network FC of the left IPL mediated the association between the covariance of anxiety and depression symptoms and sleep quality. To conclude, the FC of the left IPL may be a potential neural substrate in the association between the covariance of anxiety and depression symptoms and poor sleep quality, and may serve as a potential intervention target for the treatment of sleep disturbance in the future.

Atrophy of bilateral nucleus accumbens in melancholic depression

Evidence from previous literature suggests that the nucleus accumbens (NAc), hippocampus, and amygdala play critical roles in the reward circuit. Meanwhile, it was also suggested that abnormalities in the reward circuit might be closely associated with the symptom of anhedonia of depression. However, few studies have investigated the structural alterations of the NAc, hippocampus, and amygdala in depression with anhedonia as the main clinical manifestation. Thus, the current study aimed to explore the structural changes of the subcortical regions among melancholic depression (MD) patients, especially in the NAc, hippocampus, and amygdala, to provide a theoretical basis for understanding the pathological mechanisms of MD. Seventy-two MD patients, 74 nonmelancholic depression (NMD) patients, and 81 healthy controls (HCs) matched for sex, age, and years of education were included in the study. All participants underwent T1-weighted MRI scans. Subcortical structure segmentation was performed using the FreeSurfer software. MD and NMD patients had reduced left hippocampal volume compared with HCs. Meanwhile, only MD patients had reduced bilateral NAc volumes. Moreover, correlation analyses showed correlations between left NAc volume and late insomnia and lassitude in MD patients. The reduced hippocampal volume may be related to the pathogenesis of major depressive disorder (MDD), and the reduced volume of the NAc may be the unique neural mechanism of MD. The findings of the current study suggest that future studies should investigate the different pathogenic mechanisms of different subtypes of MDD further to contribute to the development of individualized diagnostic and treatment protocols.

Frequency-resolved connectome alterations in major depressive disorder: A multisite resting fMRI study

BACKGROUND

Functional connectome studies have revealed widespread connectivity alterations in major depressive disorder (MDD). However, the low frequency bandpass filtering (0.01-0.08 Hz or 0.01-0.1 Hz) in most studies have impeded our understanding on whether and how these alterations are affected by frequency of interest.

METHODS

Here, we performed frequency-resolved (0.01-0.06 Hz, 0.06-0.16 Hz and 0.16-0.24 Hz) connectome analyses using a large-sample resting-state functional MRI dataset of 1002 MDD patients and 924 healthy controls from seven independent centers.

RESULTS

We reported significant frequency-dependent connectome alterations in MDD in left inferior parietal, inferior temporal, precentral, and fusiform cortices and bilateral precuneus. These frequency-dependent connectome alterations are mainly derived by abnormalities of medium- and long-distance connections and are brain network-dependent. Moreover, the connectome alteration of left precuneus in high frequency band (0.16-0.24 Hz) is significantly associated with illness duration.

LIMITATIONS

Multisite harmonization model only removed linear site effects. Neurobiological underpinning of alterations in higher frequency (0.16-0.24 Hz) should be further examined by combining fMRI data with respiration, heartbeat and blood flow recordings in future studies.

CONCLUSIONS

These results highlight the frequency-dependency of connectome alterations in MDD and the benefit of examining connectome alteration in MDD under a wider frequency band.

Apathy in melancholic depression and abnormal neural activity within the reward-related circuit

Major depressive disorder is a heterogeneous syndrome, of which the most common subtype is melancholic depression (MEL). Previous studies have indicated that anhedonia is frequently a cardinal feature in MEL. As a common syndrome of motivational deficit, anhedonia is closely associated with dysfunction in reward-related networks. However, little is currently known about apathy, another syndrome of motivational deficits, and the underlying neural mechanisms in MEL and non-melancholic depression (NMEL). Herein, the Apathy Evaluation Scale (AES) was used to compare apathy between MEL and NMEL. On the basis of resting-state functional magnetic resonance imaging, functional connectivity strength (FCS) and seed-based functional connectivity (FC) were calculated within reward-related networks and compared among 43 patients with MEL, 30 patients with NMEL, and 35 healthy controls. Patients with MEL had higher AES scores than those with NMEL (t = -2.20, P = 0.03). Relative to NMEL, MEL was associated with greater FCS (t = 4.27, P < 0.001) in the left ventral striatum (VS), and greater FC of the VS with the ventral medial prefrontal cortex (t = 5.03, P < 0.001) and dorsolateral prefrontal cortex (t = 3.18, P = 0.005). Taken together the results indicate that reward-related networks may play diverse pathophysiological roles in MEL and NMEL, thus providing potential directions for future interventions in the treatment of various depression subtypes.

Abnormal functional connectivity of the nucleus accumbens subregions mediates the association between anhedonia and major depressive disorder

BACKGROUND

The nucleus accumbens (Nac) is a crucial brain region in the pathophysiology of major depressive disorder (MDD) patients with anhedonia. However, the relationship between the functional imaging characteristics of Nac subregions and anhedonia remains unclear. Thus, this study aimed to investigate the role of resting-state functional connectivity (rsFC) of the Nac subregions between MDD and anhedonia.

METHODS

We performed resting-state functional magnetic resonance imaging (fMRI) to measure the rsFC of Nac subregions in 55 MDD patients and 30 healthy controls (HCs). A two-sample t test was performed to determine the brain regions with varying rsFC among Nac subregions between groups. Then, correlation analyses were carried out to investigate the relationships between the aberrant rsFC of Nac subregions and the severity of anhedonia. Furthermore, we constructed a mediation model to explain the role of the aberrant rsFC of Nac subregions between MDD and the severity of anhedonia.

RESULTS

Compared with the HC group, decreased rsFC of Nac subregions with regions of the prefrontal cortex, insula, lingual gyrus, and visual association cortex was observed in MDD patients. In the MDD group, the rsFC of the right Nac shell-like subregions with the middle frontal gyrus (MFG)/superior frontal gyrus (SFG) was correlated with consummatory anhedonia, and the rsFC of the Nac core-like subdivisions with the inferior frontal gyrus (IFG)/insula and lingual gyrus/visual association cortex was correlated with anticipatory anhedonia. More importantly, the functional alterations in the Nac subregions mediated the association between anhedonia and depression.

CONCLUSIONS

The present findings suggest that the functional alteration of the Nac subregions mediates the association between MDD and anhedonia, which provides evidence for the hypothesis that MDD patients have neurobiological underpinnings of reward systems that differ from those of HCs.