Two recent papers (June 2021) by groups in the USA have shown how a multi-beam electron microscope such as the MultiSEM from Zeiss, when combined with the automated ultramicrotome preparation of serial sections and powerful image segmentation algorithms can provide unprecedented data about how neurons in the brain connect to provide function – examples of the research area known as ‚connectomics‘.

See

A Browsable PetascaleReconstruction of the Human Cortex  by A Shapson-Coe et al. (J W Lichtman group at Harvard University), with this associated blog entry from Google

and

Double cones and the diverse connectivityof photoreceptors and bipolar cells in an avian retina, A Gunther et al. Journal of Neuroscience, 2021.

Image source: A connectomic study of a petascale fragment of human cerebral cortex. Preprint available at bioRxiv: https://doi.org/10.1101/2021.05.29.446289