Brain Structure & Function最新文献

The mammalian mesocortex (MCx) was redefined recently as a complete ring intercalated between the allo- and iso-cortex, attending to the consistent expression of 46 selective gene markers. The MCx exhibits various other characteristics such as low myelin content of its fibers, a property directly related to its function and susceptibility to degenerative disorders. Irrespective of its shared molecular profile, the MCx ring differentiates into different sectors with singular molecular and cytoarchitectonic characteristics, such as the posterior orbitary cortex, the cingulate cortex, and the insula. In the present study, using anterograde connectivity experiments published in an Allen Institute for Brain Science public database ( https://brain-map.org/our-research/connectivity ), we analyzed the internal connectivity of the mesocortical ring. We observed that its different sectors are multiply interconnected, possibly achieving integrative functions. The medial posterior orbitary cortex stands out; it appears to play a higher hierarchical role within the MCx ring by sending and receiving projections from all mesocortical sectors.

Until the discovery of white matter neurons (WMN) in the 19th century, white matter (WM) was considered to be completely devoid of neuronal cell bodies. Despite evidence consistently showing neuronal soma within cortical WM and their purported implication in neuropsychiatric disorders, these neurons are understudied and have not been characterized in human long-range WM tracts. Using postmortem human brain tissue, we investigated the presence, densities and proportions of excitatory/inhibitory neurons in the uncinate fasciculus (UF) and corpus callosum (CC). We also investigated the ventromedial prefrontal cortex (vmPFC) to validate our methods by comparing our results with previously reported densities of neurons in cortical WM. To identify WMN, we employed fluorescence in situ hybridization with excitatory (SLC17A7) and inhibitory (GAD1) neuronal markers and subsequently validated these neurons at the protein level with NeuN immunohistochemistry. We found that the density of WMN in the vmPFC corresponded with previous independent estimates. The UF displayed a similar, though slightly lower density of WMN compared to the vmPFC, while the CC had a far lower density of WMN than both of these regions. Due to the higher-than-expected density of WMN in the UF, we validated the findings at a second location along the UF temporal segment and confirmed the presence of substantial numbers of WMN in this tract. This research constitutes the first ever validated observation of WMN in human long-range WM tracts, laying the foundation for future research on the phenotype and function of these neurons, and how they may be affected in brain disorders.

Perceiving the direction of observed actions is critical for interpreting intentions and understanding everyday actions. While direction selectivity has been extensively studied with simple stimuli such as dots, gratings, or point-light displays (PLDs), little is known about how the brain encodes direction in naturalistic, repetitive actions that are seen frequently in daily life. The present fMRI study investigated direction-selective representations during observation of complex actions performed along three bidirectional dimensions (left-right, up-down, front-back) within a 96-video stimulus set. The brain activity was analyzed using multivariate pattern analysis (MVPA) and multiple regression representational similarity analysis (RSA). MVPA revealed above-chance classification of action direction across occipital, parietal, and motor cortices, with the highest decoding in occipital, primary motor, and somatosensory regions. Crucially, RSA demonstrated that when accounting for low-level and motor features, direction information was still represented in early visual cortex, occipito-temporal areas, parietal regions, and motor-related regions. These findings indicate that action direction is represented across multiple levels of the action observation network (AON), extending from early sensory regions to higher-order parietal and frontal cortices. By using naturalistic, repetitive action videos, this study provides new evidence that the coding of action direction in the human brain is broadly distributed, reflecting the complexity of perceiving actions in everyday life. These findings suggest that direction selectivity is a core feature of the action observation network, linking basic motion processing with higher-level action understanding.

High fructose intake has been linked to metabolic and cognitive disturbances, yet its effects on hippocampal synaptic architecture remain unclear. We examined whether four weeks of fructose feeding alter metabolic parameters or CA1 synaptic ultrastructure in adult rats maintained on isocaloric AIN-93G diets containing fructose, glucose, or starch as the primary carbohydrate source. Serum biochemical and hormonal profiles showed only modest, diet-specific differences without major metabolic disruption. Quantitative electron microscopy revealed similar dendritic spine density, postsynaptic density length, perforated synapse frequency, and multisynaptic bouton density across groups, whereas fructose-fed rats displayed a small but significant reduction in spine area and an alteration in circularity. These localized geometric changes occurred without broader synaptic remodeling. Overall, our findings indicate that short-term fructose exposure under metabolically controlled, solid-diet conditions produces minimal metabolic and ultrastructural effects, in contrast to the pronounced disturbances reported in metabolically stressful paradigms, suggesting that structural consequences of fructose depend strongly on dietary context and metabolic load.

As global competition intensifies, work-related stress and burnout have become increasingly prevalent, yet their neural correlates remain poorly understood. Drawing on the Conservation of Resources (COR) theory as a conceptual framework, this study examined whether white-matter integrity in executive-function-related brain tracts statistically mediates the associations between workload, resource use, and burnout. Using cross-sectional diffusion MRI data from 188 healthy adults in Japan, we focused on fractional anisotropy (FA) in the superior longitudinal fasciculus (SLF), internal capsule (IC), and external capsule (EC), which have been consistently linked to executive functioning. Correlation and mediation analyses revealed that higher workload was negatively associated with FA in the SLF, IC, and EC, whereas FA in these tracts was negatively associated with cynicism, a core dimension of burnout. Resource use was positively associated with FA in the SLF. Mediation analyses further indicated that FA in the SLF, IC, and EC partially mediated the association between workload and cynicism, and that FA in the SLF fully mediated the association between resource use and cynicism. No comparable mediation effects were observed for exhaustion or professional efficacy. These findings should be interpreted as associative rather than causal. FA is not conceptualized as a resource itself, but as a neural correlate of executive-function capacity that covaries with psychological resource dynamics. By integrating a well-established stress-behavior framework with structural neuroimaging, this study provides an initial interdisciplinary perspective on how work-related demands, resource utilization, and burnout-related attitudes align with individual differences in white-matter integrity.

Language has referential and emotive uses. Referential language depicts events and can be verified or falsified by comparison with the event, whereas emotive language lacks the events upon which one can determine the truth value of the sentence. Using functional magnetic resonance imaging (fMRI), we investigated the brain mechanisms of the processing of the two semantically distinct forms of language in a paradigm of empathy for pain conveyed through single short sentences. In the emotive condition, subjective expressions of pain, such as "I have a toothache", were used. In the referential condition, an objective description of events in which an individual would experience pain, such as "I cut my finger", were presented. Assuming each stimulus elicits activation proportional to pain intensity ratings, we combined referential and emotive conditions and performed an analysis with a parametric modulation model. It revealed activation in the anterior cingulate cortex and, slightly below the threshold, the anterior insula, that are involved in the perception of one's own pain. Without pooling the two conditions, only the referential condition yielded activation in the two regions. Crucially, although both emotive and referential language activated multiple regions, emotive sentences activated the right temporoparietal junction, whereas referential sentences activated the precuneus/retrosplenial cortex, parahippocampal cortex, and the language network in the left hemisphere. These results suggest that a complementary interhemispheric network supports the processing of both types of language.

Depression involves impaired cognitive, affective, and social functions associated with aberrant brain network interactions. The temporoparietal junction (TPJ), a multisensory integration hub, exhibits depression-related connectivity alterations, yet the roles of its subregions during subclinical stages remain unclear. This study examined TPJ subregional communication in non-clinical high-depression individuals. Resting-state fMRI data from 586 medication-free young adults were analyzed. Participants were divided into high-depression (HD, N = 130) and low-depression (LD, N = 130) groups using Beck Depression Inventory scores. TPJ was parcellated into anterior (aTPJ), posterior (pTPJ), and ventral (vTPJ) subregions via community detection. Multi-metric connectivity (functional connectivity/FC, total interdependence/TI, Granger causality/GC) seeded from TPJ subregions was compared between groups. Support vector machine (SVM) fusion analysis identified high-contribution features for network alteration modeling. TPJ subregions showed depression-related connectivity patterns: (1) Altered default mode network DMN interactions featuring enhanced anterior DMN (medial prefrontal cortex) connectivity and weakened posterior DMN (posterior cingulate/precuneus) connectivity; (2) Disrupted left TPJ-reward pathway communication (ventral striatum, putamen, amygdala); (3) Right TPJ/left vTPJ hyperconnectivity with cognitive control systems (frontoparietal network, orbitofrontal cortex, anterior cingulate cortex); (4) Enhanced somatosensory-motor connectivity with reduced visual/auditory input; (5) Impaired intra-TPJ communication. TPJ subregions exhibit distinct dysconnectivity patterns in non-clinical depression, affecting self-referential processing, reward integration, and cognitive control. Multi-metric profiling identifies TPJ as a potential pathophysiological biomarker.