Neural correlates of posttraumatic anhedonia symptoms: Decreased functional connectivity between ventral pallidum and default mode network regions

Mediodorsal thalamus and ventral pallidum contribute to subcortical regulation of the default mode network

Humans and other animals readily transition from externally to internally focused attention, and these transitions are accompanied by activation of the default mode network (DMN). The DMN was considered a cortical network, yet recent evidence suggests subcortical structures are also involved. We investigated the role of ventral pallidum (VP) and mediodorsal thalamus (MD) in DMN regulation in tree shrew, a close relative of primates. Electrophysiology and deep learning-based classification of behavioral states revealed gamma oscillations in VP and MD coordinated with gamma in anterior cingulate (AC) cortex during DMN states. Cross-frequency coupling between gamma and delta oscillations was higher during DMN than other behaviors, underscoring the engagement of MD, VP and AC. Our findings highlight the importance of VP and MD in DMN regulation, extend homologies in DMN regulation among mammals, and underline the importance of thalamus and basal forebrain to the regulation of DMN.

Microstructural and functional alterations of the ventral pallidum are associated with levodopa-induced dyskinesia in Parkinson's disease

BACKGROUND AND PURPOSE

The ventral pallidum (VP) regulates involuntary movements, but it is unclear whether the VP regulates the abnormal involuntary movements in Parkinson's disease (PD) patients who have levodopa-induced dyskinesia (LID). To further understand the role of the VP in PD patients with LID (PD-LID), we explored the structural and functional characteristics of the VP in such patients using multimodal magnetic resonance imaging (MRI).

METHODS

Thirty-one PD-LID patients, 39 PD patients without LID (PD-nLID), and 28 healthy controls (HCs) underwent T1-weighted MRI, quantitative susceptibility mapping, multi-shell diffusion MRI, and resting-state functional MRI (rs-fMRI). Different measures characterizing the VP were obtained using a region-of-interest-based approach.

RESULTS

The left VP in the PD-LID group showed significantly higher intracellular volume fraction (ICVF) and isotropic volume fraction (IsoVF) compared with the PD-nLID and HC groups. Rs-MRI revealed that, compared with the PD-nLID group, the PD-LID group in the medication 'off' state had higher functional connectivity (FC) between the left VP and the left anterior caudate, left middle frontal gyrus and left precentral gyrus, as well as between the right VP and the right posterior ventral putamen and right mediodorsal thalamus. In addition, the ICVF values of the left VP, the FC between the left VP and the left anterior caudate and left middle frontal gyrus were positively correlated with Unified Dyskinesia Rating Scale scores.

CONCLUSION

Our multimodal imaging findings show that the microstructural changes of the VP (i.e., the higher ICVF and IsoVF) and the functional change in the ventral striatum-VP-mediodorsal thalamus-cortex network may be associated with pathophysiological mechanisms of PD-LID.

Uncovering the Neural Correlates of Anhedonia Subtypes in Major Depressive Disorder: Implications for Intervention Strategies

Major depressive disorder (MDD) represents a serious public health concern, negatively affecting individuals' quality of life and making a substantial contribution to the global burden of disease. Anhedonia is a core symptom of MDD and is associated with poor treatment outcomes. Variability in anhedonia components within MDD has been observed, suggesting heterogeneity in psychopathology across subgroups. However, little is known about anhedonia subgroups in MDD and their underlying neural correlates across subgroups. To address this question, we employed a hierarchical cluster analysis based on Temporal Experience of Pleasure Scale subscales in 60 first-episode, drug-naive MDD patients and 32 healthy controls. Then we conducted a connectome-wide association study and whole-brain voxel-wise functional analyses for identified subgroups. There were three main findings: (1) three subgroups with different anhedonia profiles were identified using a data mining approach; (2) several parts of the reward network (especially pallidum and dorsal striatum) were associated with anticipatory and consummatory pleasure; (3) different patterns of within- and between-network connectivity contributed to the disparities of anhedonia profiles across three MDD subgroups. Here, we show that anhedonia in MDD is not uniform and can be categorized into distinct subgroups, and our research contributes to the understanding of neural underpinnings, offering potential treatment directions. This work emphasizes the need for tailored approaches in the complex landscape of MDD. The identification of homogeneous, stable, and neurobiologically valid MDD subtypes could significantly enhance our comprehension and management of this multifaceted condition.

The sex differences in anhedonia in major depressive disorder: A resting-state fMRI study

OBJECTIVE

The external behavioural manifestations and internal neural mechanisms of anhedonia are sexually dimorphic. This study aimed to explore the sex differences in the regional brain neuroimaging features of anhedonia in the context of major depressive disorder (MDD).

METHOD

The resting-fMRI by applying amplitude of low-frequency fluctuation (ALFF) method was estimated in 414 patients with MDD (281 high anhedonia [HA], 133 low anhedonia [LA]) and 213 healthy controls (HC). The effects of two factors in patients with MDD were analysed using a 2 (sex: male, female) × 2 (group: HA, LA) ANOVA concerning the brain regions in which statistical differences were identified between patients with MDD and HC. We followed up with patients with HA at baseline, and 43 patients completed a second fMRI scan in remission. Paired t-test was performed to compare the ALFF values of anhedonia-related brain regions between the baseline and remission periods.

RESULTS

For the sex-by-group interaction, the bilateral insula, right hippocampus, right post cingulum cortex, and left putamen showed significant differences. Furthermore, the abnormally elevated ALFF values in anhedonia-related brain regions at baseline decreased in remission.

CONCLUSION

Our findings point to the fact that the females showed unique patterns of anhedonia-related brain activity compared to males, which may have clinical implications for interfering with the anhedonia symptoms in MDD. Using task fMRI, we can further examine the distinct characteristics between consumption anhedonia and anticipation anhedonia in MDD.

Neural Correlates of Reward Processing in the Onset, Maintenance, and Treatment of Posttraumatic Stress Disorder

Posttraumatic stress disorder (PTSD) is a prevalent, debilitating, and heterogeneous psychiatric condition marked by both exaggerated threat responding and diminished positive affect. While symptom profiles of PTSD differ across individuals, symptoms also vary within individuals over the course of illness. Functional magnetic resonance imaging studies have provided crucial insights into the neurobiology of heightened threat responsivity in PTSD, which has aided in identifying neurobiological risk factors and treatment targets for this disorder. Despite this demonstrated utility, the application of functional magnetic resonance imaging to understanding deficits in reward responsivity in PTSD remains underexplored. Significantly, over 60% of individuals with PTSD experience anhedonia, or an inability to feel pleasure, which may reflect reward processing deficits. To better understand the neural underpinnings of reward deficits and their relevance to the onset, maintenance, and treatment of PTSD, we reviewed the functional magnetic resonance imaging literature through the framework of disease prognosis. Here, we provide insights on whether reward deficits are central to PTSD or are better explained by comorbid major depressive disorder, and we clarify how reward-related deficiencies in PTSD fit into the context of more intensely studied threat-related deficits.

Aberrant interhemispheric functional connectivity in major depressive disorder with and without anhedonia

OBJECTIVE

Anhedonia is a core feature of major depressive disorder (MDD), and as a subtype of depression, MDD with anhedonia may have exceptional neurobiological mechanisms. However, the neuropathology of anhedonia in MDD remains unclear. Thus, this study aimed to investigate the brain functional differences between MDD with and without anhedonia.

METHODS

A total of 62 individuals including 22 MDD patients with anhedonia, 20 MDD patients without anhedonia, and 20 healthy controls (HCs) were recruited for this study. All participants underwent 3.0-T functional magnetic resonance imaging scan. Voxel-mirrored homotopic connectivity (VMHC) was employed to quantitatively describe bilateral functional connectivity. Analyses of variance (ANOVA) were performed to obtain brain regions with significant differences among three groups and then post hoc tests were calculated for inter-group comparisons.

RESULTS

The ANOVA revealed significant VMHC differences among three groups in the bilateral middle temporal gyrus (MTG), superior frontal gyrus (SFG), and inferior parietal lobule (IPL) (F = 10.47 ~ 15.09, p < 0.05, AlphaSim corrected). Relative to HCs, MDD with anhedonia showed significantly decreased VMHC in the bilateral MTG (t = -5.368, p < 0.05, AlphaSim corrected), as well as increased VMHC in the bilateral SFG (t = -4.696, p < 0.05, AlphaSim corrected). Compared to MDD without anhedonia, MDD with anhedonia showed significantly decreased VMHC in the bilateral MTG and IPL (t = -5.629 ~ -4.330, p < 0.05, AlphaSim corrected), while increased VMHC in the bilateral SFG (t = 3.926, p < 0.05, AlphaSim corrected). However, no significant difference was found between MDD without anhedonia and HCs.

CONCLUSION

The present findings suggest that MDD with and without anhedonia exhibit different patterns of interhemispheric connectivity. Anhedonia in MDD is related to aberrant interhemispheric connectivity within brain regions involved in the frontal-temporal-parietal circuit.

Shape analysis of the subcortical structures in North Korean refugees with post-traumatic stress disorder and major depressive disorder

BACKGROUND

Despite the growing number of refugees and their mental health issues, neurobiological mechanisms to explain clinical symptoms resulting from traumatic events, such as post-traumatic stress disorder (PTSD) or major depressive disorder (MDD), have not been extensively investigated. Research on the mental health of North Korean refugees (NKRs) who defected to South Korea for resettlement is still at an early stage but commonly reports structural and functional abnormalities in brain regions related to reward and motivational processing. The nucleus accumbens (NAc) and ventral pallidum (VP) are the major sites in subcortical structures that play key roles in reward and motivation.

METHODS

The present study examined subcortical structural abnormalities of 28 NKRs and age-, sex- matched South Korean Controls (SKCs) using shape analysis at the vertex level.

RESULTS

Among the 28 NKRs, 18 had psychiatric disorders, including PTSD and MDD. The NKRs showed significantly reduced volumes in the right NAc and bilateral VP compared to the SKRs. The volume of the right VP showed a significant negative correlation with current PTSD severity in the NKR group.

CONCLUSIONS

Our findings demonstrated that structural alterations of the NAc and VP may explain PTSD and MDD observed in the refugees and further suggest that the aftereffect of trauma, manifested as anhedonia and anxiety, may show chronically.

Correlations between facial emotion processing and biochemical abnormalities in untreated adolescent patients with major depressive disorder: A proton magnetic resonance spectroscopy study

BACKGROUND

Studies show that disturbances of the fronto-striato-thalamic-cerebellar circuit could be correlated to facial emotion processing (FEP) biases in major depressive disorder (MDD). Nevertheless, the underlying mechanism of natural metabolism-emotion relationships in adolescent MDD remains unclear.

METHODS

Thirty-seven adolescent patients with MDD and 30 healthy controls completed FEP tasks using the Chinese Facial Affective Picture System (CAFPS). Proton magnetic resonance spectroscopy (¹H-MRS) was also used to obtain ratios of N-acetylaspartate (NAA) /creatine (Cr) and choline (Cho) /Cr ratios in the prefrontal cortex (PFC), anterior cingulate cortex (ACC), putamen, thalamus and cerebellum. Correlations between abnormal neurometabolic ratios and FEP were also computed.

RESULTS

Compared with the control group, the MDD group had significantly lower accuracy and perception intensity of happiness, and significantly higher accuracy of disgust and perception intensity of sad and fearful faces in FEP tasks. Compared to healthy controls, adolescent patients with MDD showed significantly lower NAA/Cr ratios in the left PFC, higher NAA/Cr ratios in the right thalamus, and higher Cho/Cr ratios in the right putamen, although there were no significant differences in metabolites in the ACC and cerebellum between two groups. In the MDD group, NAA/Cr ratios of the right thalamus were negatively correlated with happy reaction time and positively correlated with sad, anger, and fear intensity; Cho/Cr ratios in the right putamen were positively correlated with fear reaction time.

CONCLUSIONS

Our findings suggest that FEP bias may exist in adolescents with MDD, while the impairment of FEP may be associated with abnormal metabolites in the fronto-striato-thalamic circuit.