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Front Neural Circuits. 2015 Apr 29;9:17. doi: 10.3389/fncir.2015.00017. eCollection 2015.

Spatial organization of excitatory synaptic inputs to layer 4 neurons in mouse primary auditory cortex.

Author information

1
Department of Otolaryngology/Head and Neck Surgery, University of North Carolina at Chapel Hill Chapel Hill, NC, USA ; The Curriculum in Neurobiology, University of North Carolina Chapel Hill, NC, USA.
2
Department of Otolaryngology/Head and Neck Surgery, University of North Carolina at Chapel Hill Chapel Hill, NC, USA ; The Curriculum in Neurobiology, University of North Carolina Chapel Hill, NC, USA ; Department of Cell Biology and Physiology, University of North Carolina Chapel Hill, NC, USA.

Abstract

Layer 4 (L4) of primary auditory cortex (A1) receives a tonotopically organized projection from the medial geniculate nucleus of the thalamus. However, individual neurons in A1 respond to a wider range of sound frequencies than would be predicted by their thalamic input, which suggests the existence of cross-frequency intracortical networks. We used laser scanning photostimulation and uncaging of glutamate in brain slices of mouse A1 to characterize the spatial organization of intracortical inputs to L4 neurons. Slices were prepared to include the entire tonotopic extent of A1. We find that L4 neurons receive local vertically organized (columnar) excitation from layers 2 through 6 (L6) and horizontally organized excitation primarily from L4 and L6 neurons in regions centered ~300-500 μm caudal and/or rostral to the cell. Excitatory horizontal synaptic connections from layers 2 and 3 were sparse. The origins of horizontal projections from L4 and L6 correspond to regions in the tonotopic map that are approximately an octave away from the target cell location. Such spatially organized lateral connections may contribute to the detection and processing of auditory objects with specific spectral structures.

KEYWORDS:

brain slice; glutamate uncaging; intracortical circuits; neocortical circuits; patch clamp; spectral integration; thalamocortical recipient neurons

PMID:
25972787
PMCID:
PMC4413692
DOI:
10.3389/fncir.2015.00017
[Indexed for MEDLINE]
Free PMC Article
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