In the present study we have used Focused Ion Beam/Scanning Electron Microscopy (FIB/SEM) to perform a study of the synaptic organization of layer III of Brodmann’s area 21 in human. We analyzed the synaptic density, 3D spatial distribution, and type (excitatory/inhibitory), as well as the shape and size of each synaptic junction of 4945 synapses that were fully reconstructed in 3D. Moreover, the postsynaptic targets of 1888 synapses were determined. We also compared several electron microscopy methods and analysis tools to estimate the synaptic density in the same brain tissue. We have shown that FIB/SEM is much more reliable and robust than the majority of the other commonly used EM techniques. The present work constitutes a detailed description of the synaptic organization of cortical layer III. Further studies on the rest of the cortical layers are necessary to better understand the functional organization of this temporal cortical region.
bioRxiv Subject Collection: Neuroscience