Cerebral Cortex Advance Access published online on April 9, 2007
Cerebral Cortex, doi:10.1093/cercor/bhm027
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Local Potential Connectivity in Cat Primary Visual Cortex
1 Physics Department and Center for Interdisciplinary Research on Complex Systems, Northeastern University, Boston, MA 02115, USA, 2 Department of Biological Sciences, University of South California, Los Angeles, CA 90089, USA, 3 Instituto de Neurociencias de Alicante, Consejo Superior de Investigaciones Cientificas, Universidad Miguel Hernandez, 03550 Sant Joan d'Alacant, Spain, 4 Abteilung für Neurophysiologie, Ruhr-Universität Bochum, 44801 Bochum, Germany, 5 Department of Anatomy, Histology, and Embryology, University of Debrecen, 4032 Debrecen, Hungary, 6 Department of Anatomy and Physiology, Medical Faculty, Laval University, Quebec, G1K-7P4 Canada, 7 Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA
Address correspondence to Armen Stepanyants, Email: a.stepanyants{at}neu.edu.
Time invariant description of synaptic connectivity in cortical circuits may be precluded by the ongoing growth and retraction of dendritic spines accompanied by the formation and elimination of synapses. On the other hand, the spatial arrangement of axonal and dendritic branches appears stable. This suggests that an invariant description of connectivity can be cast in terms of potential synapses, which are locations in the neuropil where an axon branch of one neuron is proximal to a dendritic branch of another neuron. In this paper, we attempt to reconstruct the potential connectivity in local cortical circuits of the cat primary visual cortex (V1). Based on multiple single-neuron reconstructions of axonal and dendritic arbors in 3 dimensions, we evaluate the expected number of potential synapses and the probability of potential connectivity among excitatory (pyramidal and spiny stellate) neurons and inhibitory basket cells. The results provide a quantitative description of structural organization of local cortical circuits. For excitatory neurons from different cortical layers, we compute local domains, which contain their potentially pre- and postsynaptic excitatory partners. These domains have columnar shapes with laminar specific radii and are roughly of the size of the ocular dominance column. Therefore, connections between most excitatory neurons in the ocular dominance column can be implemented by local synaptogenesis. Structural connectivity involving inhibitory basket cells is generally weaker than excitatory connectivity. Here, only nearby neurons are capable of establishing more than one potential synapse, implying that within the ocular dominance column these connections have more limited potential for circuit remodeling.
Key Words: excitatory • inhibitory • interlaminar connectivity • morphology • neurogeometry
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