Narayanan Kasthuri and a team of researchers from Harvard, MIT, Duke, and John Hopkins universities, fully reconstructed all the neuron sections and many sub-cellular objects, including synapses and synapse vesicles, in a volume of 1500 µm3 (which is just a little more than one millionth of a cubic millimeter) using 3×3×30 nm voxels.
The results, published in an article in the journal Cell, in July 2015, describe the experimental procedure and the conclusions. The data was obtained by collecting 2,250 brain slices, each roughly 30 nm thick, obtained with a tape-collecting ultramicrotome that slices brain sections using a diamond knife.The slices were imaged using serial electron microscopy and the images processed in order to reconstruct a number of volumes. In this volume, the authors have reconstructed the 3D structure of the 1500 µm3 of neural tissue, which included hundreds of dendrites, more than 1400 neuron axons and 1700 synapses, which corresponds to about one synapse per cubic micron.
(Rendering by the authors, used with permission)