Brain Structure & Function最新文献

The cellular connectivity of the human visual cortex remains largely uncharted, with most insights derived from animal models. A custom-designed tracer electrophoresis setup for polar lipophilic tracers enabled the reconstruction of fiber tracts in fixed postmortem human brains, visualizing their trajectories across previously unmapped distances, from cellular origins to axonal terminations. Applied to the occipital lobe, four pathways of the calcarine cortex were demonstrated: the stratum calcarinum, stratum proprium cunei, fasciculus transversus cunei, and the fasciculus transversus gyri lingualis. Specifically, axonal projections from granular and supragranular layers of the calcarine cortex were traced to the granular and supragranular layers of the cuneus, inferior, middle, and superior occipital, lingual, and fusiform gyri. Additionally, infra- and supragranular feedback projections from the prestriate cortex to the supragranular layer of the calcarine cortex were identified. These results extend previous descriptions by offering the first cellular-level evidence for intrahemispheric pathways in the human occipital lobe.

Genetic studies have increasingly identified key mechanisms that underlie individual and phylogenetic variation in behavioral and brain phenotypes. Here, we used quantitative genetics to estimate heritability in whole brain and region-specific variation in gray matter in a sample of captive chimpanzees. We included the contributions of sex and age to individual variation in gray matter as well as their association with cognition and motor functions and found small to moderate heritability in average gray matter volume in the majority of brain regions. By contrast, weaker estimates of heritability were found when considering asymmetries in gray matter across brain regions. Age was inversely associated with gray matter volume for the frontal lobe and the basal forebrain after accounting for sex and relatedness of the chimpanzees. Chimpanzees that had higher cognition scores were found to have greater leftward asymmetries in the regions comprising the frontal lobe and basal forebrain component. Further, chimpanzees with better performance on a tool use task had higher gray matter volumes in the frontal and basal forebrain regions. However, no genetic associations were found between tool use performance or cognition and the average frontal or basal forebrain gray matter volumes or asymmetry.

Mental imagery is widely used in cognitive neuroscience and rehabilitation studies, yet their neural mechanisms remain not fully understood. In this study, we investigated neural correlates of motor and tactile imagery using simultaneous electroencephalography (EEG) and functional near-infrared spectroscopy (fNIRS) recordings. A total of 16 healthy participants performed motor and tactile imagery tasks while brain activity was assessed. We analyzed event-related desynchronization (ERD) of the mu-rhythm and hemodynamic responses in sensory-motor regions. Similar spatio-temporal EEG patterns were observed for both motor and tactile imagery conditions (e.g., prominent contralateral ERD at C3). Hemodynamic responses differed: motor imagery elicited activation in both precentral and postcentral regions (p = 0.433), whereas tactile imagery predominantly engaged postcentral regions. The latter effect reached significance only in the functional channels of interest (fCOI) analysis (p = 0.003) and showed a non-significant trend across the full anatomical channel groups (p = 0.101). Correlation analysis revealed a strong across-subject correlation (r = 0.84; p < 0.001) between ERD values in motor and tactile imagery, but no correlation between ERD and hemodynamic responses. Linear mixed model analysis revealed significant (p < 0.001) associations between precentral and postcentral HRs for both MI and TI. These findings suggest that although motor and tactile imagery share common sensorimotor engagement at the electrophysiological level, their hemodynamic signatures are distinct. The absence of linear associations between modalities highlights the complexity of brain dynamics and the importance of multimodal assessments. The findings have implications for the design of brain-computer interfaces and rehabilitation protocols using mental imagery.

In the macaque brain most cortical areas are connected through the corpus callosum to the same or different areas of the contralateral hemisphere (homotopic and heterotopic callosal connections). Many studies have described the callosal connectivity of several cortical areas, but the proportion of callosal vs. ipsilateral afferences and, except for frontal motor areas, of homotopic vs. heterotopic afferences is still unknown. We have analyzed qualitatively and quantitatively the distribution of callosal projecting neurons (CPNs) after neural tracer injections in prefrontal, frontal motor and opercular, and parietal areas (36 tracer injections in 20 macaques). The percentage of CPNs with respect to the total number of labeled neurons (ipsi + contra), with few exceptions, was at least 5% and though quite variable tended to be higher for prefrontal (~ 17%) and premotor (~ 14%), and lower for parietal (~ 9%) areas. For most areas, heterotopic afferences were richer than homotopic ones and for some (e.g., F6 and F3) the areal distribution of CPNs was almost similar to that of the ipsilateral labeling. Furthermore, in areas 24, F6, and F3 the amount of CPNs tended to be relatively high. Finally, the laminar distribution of CPNs could differ from that of the ipsilateral labeling and varied according to the projecting and/or the target area. The present data provide a general framework, though still not complete, of the interhemispheric connectivity in the primate brain and could be useful for a better understanding of the interhemispheric interactions in bimanual coordination, sensorimotor integration, and cognitive functions.