Geometric and functional organization of cortical circuits.
Can neuronal morphology predict functional synaptic circuits? In the rat barrel cortex, 'barrels' and 'septa' delineate an orderly matrix of cortical columns. Using quantitative laser scanning photostimulation we measured the strength of excitatory projections from layer 4 (L4) and L5A to L2/3 pyramidal cells in barrel- and septum-related columns. From morphological reconstructions of excitatory neurons we computed the geometric circuit predicted by axodendritic overlap. Within most individual projections, functional inputs were predicted by geometry and a single scale factor, the synaptic strength per potential synapse. This factor, however, varied between projections and, in one case, even within a projection, up to 20-fold. Relationships between geometric overlap and synaptic strength thus depend on the laminar and columnar locations of both the pre- and postsynaptic neurons, even for neurons of the same type. A large plasticity potential appears to be incorporated into these circuits, allowing for functional 'tuning' with fixed axonal and dendritic arbor geometry.
Shepherd
Gordon M G
GM
Howard Hughes Medical Institute, Cold Spring Harbor, New York 11724, USA.
Stepanyants
Armen
A
Bureau
Ingrid
I
Chklovskii
Dmitri
D
Svoboda
Karel
K
D000818:Animals; D001369:Axons / Q000502:physiology / Q000648:ultrastructure; D001931:Brain Mapping; D048430:Cell Shape / Q000502:physiology; D003712:Dendrites / Q000502:physiology / Q000648:ultrastructure; D004558:Electric Stimulation; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D019044:Image Cytometry; D007834:Lasers; D008239:Lysine / Q000031:analogs & derivatives*; D009434:Neural Pathways / Q000166:cytology* / Q000502:physiology; D009473:Neuronal Plasticity / Q000502:physiology*; D009924:Organ Culture Techniques; D010775:Photic Stimulation; D017966:Pyramidal Cells / Q000166:cytology* / Q000502:physiology / Q000528:radiation effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D013003:Somatosensory Cortex / Q000166:cytology* / Q000502:physiology; D013569:Synapses / Q000502:physiology / Q000648:ultrastructure*; D009435:Synaptic Transmission / Q000502:physiology*; D014466:Ultraviolet Rays
C013411:biocytin; D008239:Lysine