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Two-photon calcium imaging and electron microscopy were used to explore the relationship between structure and function in mouse primary visual cortex, showing that layer 2/3 neurons are connected in subnetworks, that pyramidal neurons with similar orientation selectivity preferentially form synapses with each other, and that neurons with similar orientation tuning form larger synapses; this study exemplifies functional connectomics as a powerful method for studying the organizational logic of cortical networks.

Automated reconstruction of dense neural networks in the ventral nerve cord of the fruit fly provides a resource for investigating the neural control of movement.

Connectomics, the comprehensive mapping of neural circuits at nanoscale resolution, has historically relied on electron microscopy (EM), both transmission (TEM) and scanning (SEM). However, as connectomics scales towards larger brain volumes and whole mammalian brains, substantial technical challenges emerge. Here, we highlight key challenges and advancing approaches that hold promise, particularly those that integrate three-dimensional, multi-resolution and time-resolved imaging to capture both long-range and local wiring, down to supramolecular resolution.

We use connectomics to compare the wiring logic of premotor circuits controlling the Drosophila leg and wing, finding that both premotor networks cluster into modules that link motor neurons innervating muscles with related functions.

Electron microscopy (EM) is the gold standard for biological ultrastructure but acquisition speed is slow, making it unsuitable for large volumes. Here the authors present a parallel imaging pipeline for continuous autonomous imaging with six transmission EMs to image 1 mm³ of mouse cortex in less than 6 months.

Excitatory pyramidal neurons preferentially target inhibitory interneurons with the same selectivity and, in turn, inhibitory interneurons preferentially target pyramidal neurons with opposite selectivity, forming an opponent inhibition motif that supports decision-making.

Mapping of the mouse cerebellar cortex using 3D reconstruction from electron microscopy, as well as numerical simulation of neuronal activity, shows non-random redundancy of connectivity that may favour resilient learning over encoding capacity.

Kuan, Phelps, et al. used synchrotron X-ray imaging and deep learning to map dense neuronal wiring in fly and mouse tissue, enabling examination of individual cells and connectivity in circuits governing motor control and perceptual decision-making.

Comprehensive profiling of a circumventricular organ with leaky blood vessels, and comparison to cortex vasculature reveal that blood–brain barrier heterogeneity reflects differences in endothelial cells and their interactions with perivascular cells.

A consensus cell type atlas for the fly brain provides both an intellectual framework and open-source toolchains for brain-scale comparative connectomics.

Three electron microscopy datasets are combined to provide a complete connectomic description of the neural circuitry that makes up the neck connective in Drosophila, including the descending neurons, ascending neurons and sensory ascending neurons.

FlyWire presents a neuronal wiring diagram of the whole fly brain with annotations for cell types, classes, nerves, hemilineages and predicted neurotransmitters, with data products and an open ecosystem to facilitate exploration and browsing.

During segmentation of neurons in electron microscopy datasets, auxiliary learning via the prediction of local shape descriptors increases efficiency, which is important for the processing of datasets of ever-increasing size.

Candelabrum cells have remained an obscure cerebellar cell type. The authors show that candelabrum cells are the most abundant Purkinje layer interneuron, are molecularly distinct and have a connectivity that allows them to control cerebellar output.

To date, various aspects of connectivity have been inferred from electron microscopy (EM) of synaptic contacts, light microscopy of axonal and dendritic arbors, and correlations in activity. However, until now it has not been possible to relate the complex structural wiring between neurons to the function of individual cells. Using a combination of functional imaging and three-dimensional serial EM reconstruction at unprecedented scale, two papers now describe the connectivity of single cells in the mouse visual system. This study investigates the connectivity of inhibitory interneurons in primary visual cortex.

A deep-learning-based approach enables automatic identification of synaptically connected neurons in electron microscopy datasets of the fly brain.

A complete larval zebrafish brain is examined and its myelinated axons reconstructed using serial-section electron microscopy, revealing remarkable symmetry and providing a valuable resource.