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The Journal of Neuroscience, July 2, 2003, 23(13):5684-5692
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Independent Projection Streams from Macaque Striate Cortex to the Second Visual Area and Middle Temporal Area
Lawrence C. Sincich and
Jonathan C. Horton
Beckman Vision Center, University of California, San Francisco, San
Francisco, California 94143
The interareal wiring of the neocortex is usually depicted as a network of
single point-to-point connections, often side-stepping the possibility that
some neurons may project to multiple cortical areas. The prevalence of such
neurons is unknown; if they are abundant, cortical circuits are more likely to
be connectionally diffuse. We used a dual-tracer approach to determine whether
single neurons in the macaque primary visual cortex (V1) project to two
extrastriate areas, the second visual area (V2) and the middle temporal area
(MT). We found two large intermingled groups of single-labeled neurons in
layer 4B of V1 projecting independently to either V2 or MT. A third, sparser
group of double-labeled neurons projected to both areas; we termed these
manifold neurons. We also found that MT-projecting cells were distributed
indiscriminately with respect to cytochrome oxidase compartment in layer 4B,
revealing a subpopulation that provides a potential source of patch input from
V1 to MT. The results demonstrate that primary sensory cortices can use
multiple projection strategies to distribute signals to higher areas, and
suggest that feedforward projections may route signals with more specificity
than feedback pathways.
Key words: visual cortex; intracortical; manifold projections; flatmount; motion; cytochrome oxidase; patch column; interpatch column
Received Jan. 2, 2003;
revised Apr. 9, 2003;
accepted Apr. 11, 2003.
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