Neuron number increases with mammalian brain size, but how the dendritic morphology of individual neocortical pyramidal neurons changes across this range remains unclear. To address this question, we examined 2,412 neocortical pyramidal neuron reconstructions from 23 mammalian species in NeuroMorpho.Org, spanning an approximately 11,000-fold range in brain weight. At the whole-neuron level, primary axis length, lateral extent, and Sholl critical radius increased with brain size but remained far below the isometric expectation, whereas total dendritic length showed no significant association. Mean remote bifurcation angle, section tortuosity, and maximum branch order decreased with brain size, suggesting that greater spatial reach was accompanied by a more streamlined arbor organization rather than by proportional increases in dendritic cable length or branching depth. Compartment-resolved analyses localized much of the spatial, cable-length, and fixed-radius Sholl signal to basal dendrites, whereas apical spatial expansion was weaker. By contrast, branch geometry associations were broadly similar between apical and basal compartments. Together, these patterns suggest that mammalian pyramidal neuron morphology varies with brain size through selective spatial expansion and basal-dominant compartmental scaling rather than through uniform enlargement of individual arbors.
Brainhack events provide a bottom-up approach to tackle challenges in neuroscience. In 2025, the Enrico Fermi Research Center in Rome hosted its first Brainhack, with the goal of fostering interdisciplinary collaborations bringing together the physics and neuroscience perspectives on the study of brain structure and function. Structured in four days, it gave the chance to the participants to propose their own idea and shape a project based on it, leading to six research avenues: the combination of X-ray imaging and diffusion MRI algorithms to pioneer ultra-high-resolution tractography; multivariate approaches to study the shared factors between brain metabolism and microstructure estimated from MRI data; development of transfer entropy analysis-based tools for effective connectivity estimation in fMRI data; identification of brain states through Markov models; deep learning approaches to predict task EEG time courses; multi-scale network models to study functional and cerebrovascular data. Each project led to promising results and marked the beginning of new collaborations.
This study provides a unique three-dimensional characterization of the cytoarchitecture of the anterior horn of the human sacral spinal cord, with a specific focus on the S2 segment. This region is of particular interest because it constitutes the transition between the motoneurons that innervate the muscles of the lower limbs and those that control the pelvic floor. The S2 segment also contains a distinct motor nucleus, Onuf’s nucleus (ON), involved in sphincter control. Using a tissue clearing protocol combined with light sheet fluorescence microscopy, we analyzed samples of sacral spinal cords from ten human cadavers to obtain high-resolution 3D images. Segmentation revealed seven distinct motoneuron groups organized into medial and lateral divisions surrounding ON. ON itself displayed a complex, multilobed architecture, with a denser central region and more fragmented extremities. A robust cytoarchitectural pattern of specific neuron columns was identified along the rostrocaudal axis of ON and characterized by their progressive disappearance, fusion, or emergence. Notably, lateral columns predominated at the level of ON rostral half, whereas medial columns appeared more caudally. Additionally, a significant sexual dimorphism in ON length was observed, being longer in males. Overall, our findings demonstrate that the classical columnar model of spinal motoneuron organization underestimates the structural complexity of the anterior horn. This study highlights the interest of light sheet fluorescence microscopy for revealing fine anatomical organization and provides a framework for future investigations of SC cytoarchitecture.
The nucleus reuniens (RE), paraventricular nucleus of the thalamus (PVT), and perirhinal cortex (PRC), which have reciprocal connections with both the medial prefrontal cortex (mPFC) and hippocampus (HPC), could act as the relays to regulate the interplay between the mPFC and HPC. To better understand the anatomical structure of neurons in the mPFC and HPC subregions projecting to the peri-reuniens nucleus (periRE), posterior PVT (pPVT), and PRC, fluorescent retrograde tracers of CTB-AF488 or CTB-AF594 were unilaterally injected into the pPVT and PRC (Experiment 1) or into the pPVT and periRE (Experiment 2), respectively. The cell labeling was examined in the region of interest of the mPFC-HPC network, including the prelimbic cortex (PL), infralimbic cortex (IL), dorsal and ventral CA1 (dCA1 and vCA1), and dorsal and ventral subiculum (dSub and vSub). Our results indicated that mPFC projections to the periRE or pPVT were more robust on the ipsilateral side in general, with the exception of IL projections to the pPVT showing no lateralization, and the majority of the projections originated from the deep layer. There was no lateralization of mPFC projections to the PRC. As for the HPC, the majority of PRC-projecting cells were found on the ipsilateral side of the vCA1 and dSub. There was in general no lateralization of HPC projections to the periRE or pPVT, with the exception of vSub projections to the pPVT more robust on the ipsilateral side. Finally, collateral projecting cells were sparse in all regions examined of the two experiments.
