The Journal of Neuroscience, May 15, 2001, 21(10):3600-3608
Layer-Specific Input to Distinct Cell Types in Layer 6 of Monkey
Primary Visual Cortex
Farran
Briggs and
Edward M.
Callaway
Systems Neurobiology Laboratories, Salk Institute for Biological
Sciences and Department of Biology, University of California, San
Diego, La Jolla, California 92037
Layer 6 of monkey V1 contains a physiologically and anatomically
diverse population of excitatory pyramidal neurons. Distinctive arborization patterns of axons and dendrites within the functionally specialized cortical layers define eight types of layer 6 pyramidal neurons and suggest unique information processing roles for each cell
type. To address how input sources contribute to cellular function, we
examined the laminar sources of functional excitatory input onto
individual layer 6 pyramidal neurons using scanning laser
photostimulation. We find that excitatory input sources correlate with
cell type. Class I neurons with axonal arbors selectively targeting
magnocellular (M) recipient layer 4C
receive input from M-dominated
layer 4B, whereas class I neurons whose axonal arbors target
parvocellular (P) recipient layer 4C
receive input from P-dominated
layer 2/3. Surprisingly, these neuronal types do not differ
significantly in the inputs they receive directly from layers 4C or
4C. Class II cells, which lack dense axonal arbors within layer 4C,
receive excitatory input from layers targeted by their local axons.
Specifically, type IIA cells project axons to and receive input from
the deep but not superficial layers. Type IIB neurons project to and
receive input from the deepest and most superficial, but not middle
layers. Type IIC neurons arborize throughout the cortical layers and
tend to receive inputs from all cortical layers. These observations
have implications for the functional roles of different layer 6 cell
types in visual information processing.
Key words:
macaque; visual cortex; V1; layer 6; photostimulation; excitatory input; local circuits; caged glutamate
Copyright © 2001 Society for Neuroscience 0270-6474/01/21103600-09$05.00/0
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