Neurons Reach Out and Touch Everyone

3D synaptic contact_Brain
(Picture and full text from PNAS January 18, 2005 vol. 102 no. 3 880-885 )
Using multi-neuron whole-cell recordings and confocal microscopy images of rat somatosensory cortex, the authors found that the pyramidal neurons in a region called cortical layer V send out axons that touch all neighboring dendrites; they describe this process as "all-to-all" geometry. The functional synapses were characterized by the presence of synaptic boutons. These findings suggest that, within the neocortex, all possible connections already exist, though most are nonfunctional. These data provide the first direct experimental evidence for a tabula rasa-like structural matrix between neocortical pyramidal neurons and suggests that pre- and postsynaptic interactions shape the conversion between touches and synapses to form specific functional microcircuits. The authors suggest that this architecture provides the neocortex with its immense capacity for plasticity without requiring the wasteful process of axonal and dendritic remodeling.