3D ultrastructural study of synapses using FIB/SEM in the Human Cortex (Brodmann’s areas 24 and 38) (v1)

We used Focused Ion Beam/Scanning Electron Microscopy (FIB/SEM) to perform a 3D analysis of the synapses in the neuropil in layer III of the Brodmann's areas 24 and 38 of the human brain. 3 human brain autopsies cases have been used to achieve a total of 27 FIB/SEM valid images stacks. Specifically, we studied synaptic structural characteristics, which were fully reconstructed in 3D. We analyzed the synaptic density, 3D spatial distribution, and type (excitatory and inhibitory), as well as the shape and size of each synaptic junction. Moreover, their postsynaptic targets were determined. The present work constitutes a detailed description of the synaptic organization of the human cortex, which is a necessary step to better understand the functional organization of the cortex in both health and disease.