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The Journal of Neuroscience, October 29, 2008, 28(44):11174-11185; doi:10.1523/JNEUROSCI.2093-08.2008

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Behavioral/Systems/Cognitive
Excitatory Local Connections of Superficial Neurons in Rat Auditory Cortex

Dennis L. Barbour¹ and Edward M. Callaway²

¹Laboratory of Sensory Neuroscience and Neuroengineering, Washington University in St. Louis, St. Louis, Missouri 63130, and ²Systems Neurobiology Laboratories, Salk Institute for Biological Studies, La Jolla, California 92037

Correspondence should be addressed to Dr. Dennis L. Barbour, Campus Box 1097, One Brookings Drive, Washington University in St. Louis, St. Louis, MO 63130. Email: dbarbour{at}biomed.wustl.edu

The mammalian cerebral cortex consists of multiple areas specialized for processing information for many different sensory modalities. Although the basic structure is similar for each cortical area, specialized neural connections likely mediate unique information processing requirements. Relative to primary visual (V1) and somatosensory (S1) cortices, little is known about the intrinsic connectivity of primary auditory cortex (A1). To better understand the flow of information from the thalamus to and through rat A1, we made use of a rapid, high-throughput screening method exploiting laser-induced uncaging of glutamate to construct excitatory input maps of individual neurons. We found that excitatory inputs to layer 2/3 pyramidal neurons were similar to those in V1 and S1; these cells received strong excitation primarily from layers 2–4. Both anatomical and physiological observations, however, indicate that inputs and outputs of layer 4 excitatory neurons in A1 contrast with those in V1 and S1. Layer 2/3 pyramids in A1 have substantial axonal arbors in layer 4, and photostimulation demonstrates that these pyramids can connect to layer 4 excitatory neurons. Furthermore, most or all of these layer 4 excitatory neurons project out of the local cortical circuit. Unlike S1 and V1, where feedback to layer 4 is mediated exclusively by indirect local circuits involving layer 2/3 projections to deep layers and deep feedback to layer 4, layer 4 of A1 integrates thalamic and strong layer 4 recurrent excitatory input with relatively direct feedback from layer 2/3 and provides direct cortical output.

Key words: auditory cortex; rat; lamina; column; glutamate; synapse

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Received May 7, 2008; revised Aug. 7, 2008; accepted Sept. 17, 2008.

Correspondence should be addressed to Dr. Dennis L. Barbour, Campus Box 1097, One Brookings Drive, Washington University in St. Louis, St. Louis, MO 63130. Email: dbarbour{at}biomed.wustl.edu

This article has been cited by other articles:

				P. Chadderton, J. P. Agapiou, D. McAlpine, and T. W. Margrie The Synaptic Representation of Sound Source Location in Auditory Cortex J. Neurosci., November 11, 2009; 29(45): 14127 - 14135. [Abstract] [Full Text] [PDF]

				R. J. Richardson, J. A. Blundon, I. T. Bayazitov, and S. S. Zakharenko Connectivity Patterns Revealed by Mapping of Active Inputs on Dendrites of Thalamorecipient Neurons in the Auditory Cortex J. Neurosci., May 20, 2009; 29(20): 6406 - 6417. [Abstract] [Full Text] [PDF]

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