[Ultrastructural variations of synapses in the normal human cerebral cortex]

The numerous synapses in the normal human brain cortex display various aspects. The authors have also observed some electronic type synapses which are more numerous around the pericaryons. The cortical synapses are classed according to their synaptic vesicle richness : synapses with very few vesicles, synapses very rich in vesicles and synapses with a middling vesicular density. With the help of observations on these aspects and on variations of the synaptic cleft and that of the postsynaptic density, the authors advance an hypothesis on synaptic plasticity, the synaptic structures going from a simple intercellular contact (probably non functional) to a completly formed synapse and vice versa.