Cerebral Cortex Advance Access originally published online on August 18, 2004
Cerebral Cortex 2005 15(5):479-488; doi:10.1093/cercor/bhh154
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Cerebral Cortex V 15 N 5 © Oxford University Press 2004; all rights reserved
Feature Article |
Laminar Patterns of Local Excitatory Input to Layer 5 Neurons in Macaque Primary Visual Cortex
1 Systems Neurobiology Laboratories, The Salk Institute for Biological Sciences, 10010 North Torrey Pines Road, La Jolla, CA 92037, USA and 2 Department of Biology, University of California, San Diego, La Jolla, CA 92037, USA, 3 Present address: Center for Neuroscience, 1544 Newton Court, University of California, Davis, Davis, CA 95616-8768, USA
Address correspondence to: Edward M. Callaway, SNL-C, The Salk Institute, 10010 North Torrey Pines Rd., La Jolla, CA 92037, USA. Email: callaway{at}salk.edu.
Layer 5 neurons in primary visual cortex make putative reciprocal feedback connections to the superficial layers. To test this hypothesis, we employed scanning laser photostimulation combined with intracellular dye injection to examine local functional excitatory inputs to and axonal projections from individual layer 5 neurons in brain slices from monkey V1. In contrast with previous studies of other V1 neurons, layer 5 neurons received significant input from nearly all of the cortical layers, suggesting individual layer 5 cells integrate information from a broad range of input sources. Nevertheless relative strengths of laminar inputs varied across neurons. Cluster analysis of relative strength of laminar inputs to individual layer 5 neurons revealed four discrete clusters representing recurring input patterns; each cluster included both excitatory and inhibitory neurons. Twenty-five of 40 layer 5 neurons fell into two clusters, both characterized by very strong input from superficial layers. These input patterns are consistent with layer 5 neurons providing feedback to superficial layers. The remaining 15 neurons received stronger input from deep layers. Differences in input from layer 4C
versus 4Cß also suggest specific associations of the magnocellular and parvocellular visual pathways, with populations receiving stronger input from deep versus superficial cortical layers.
Key Words: circuitry • cluster analysis • inhibitory • photostimulation • pyramidal
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