title: Specialized circuits from primary visual cortex to V2 and area MT.
abstract: Primary visual cortex recombines inputs from magnocellular (M) and parvocellular (P) streams to create functionally specialized outputs. Understanding these input-output relationships is complicated by the fact that layer 4B, which provides outputs to dorsal visual areas, contains multiple cell types. Using a modified rabies virus that expresses green fluorescent protein, we show that layer 4B neurons projecting to MT are a majority spiny stellate, whereas those projecting to V2 are overwhelmingly pyramidal. Regardless of cell type, MT-projecting neurons have larger cell bodies, more dendritic length, and are deeper within layer 4B. Furthermore, MT-projecting pyramidal neurons are located preferentially underneath cytochrome oxidase blobs, indicating that MT-projecting neurons of both types restrict their dendrites to M-recipient zones. We conclude that MT-projecting layer 4B neurons are specialized for the fast transmission of information from the M pathway, while V2-projecting neurons are likely to mediate slower computations involving mixed M and P signals.
authors.affiliation: Systems Neurobiology Laboratories, The Salk Institute for Biological Studies, 10010 North Torrey Pines Road, La Jolla, CA 92037, USA.
authors.forename: Jonathan J
authors.initials: JJ
authors.lastname: Nassi
authors.forename: Edward M
authors.initials: EM
authors.lastname: Callaway
mesh_terms: D000818:Animals; D001370:Axonal Transport / Q000502:physiology; D001931:Brain Mapping / Q000379:methods; D048430:Cell Shape / Q000502:physiology; D003712:Dendrites / Q000502:physiology / Q000648:ultrastructure; D003576:Electron Transport Complex IV / Q000378:metabolism; D005822:Genetic Vectors / Q000235:genetics; D049452:Green Fluorescent Proteins / Q000235:genetics; D007395:Interneurons / Q000166:cytology / Q000502:physiology; D008251:Macaca; D009474:Neurons / Q000166:cytology* / Q000502:physiology; D017966:Pyramidal Cells / Q000166:cytology / Q000502:physiology; D011820:Rabies virus / Q000235:genetics; D013194:Staining and Labeling / Q000379:methods; D013702:Temporal Lobe / Q000166:cytology* / Q000502:physiology; D014793:Visual Cortex / Q000166:cytology* / Q000502:physiology; D014795:Visual Pathways / Q000166:cytology* / Q000502:physiology; D014796:Visual Perception / Q000502:physiology*