Abstract
The sensory neocortex consists of hierarchically-organized areas reciprocally connected via feedforward and feedback circuits. Feedforward connections shape the receptive field properties of neurons in higher areas within parallel streams specialized in processing specific stimulus attributes. Feedback connections have been implicated in top-down modulations, such as attention, prediction and sensory context. However, their computational role remains unknown, partly because we lack knowledge about rules of feedback connectivity to constrain models of feedback function. For example, it is unknown whether feedback connections maintain stream-specific segregation, or integrate information across parallel streams. Using viral-mediated labeling of feedback connections arising from specific cytochrome-oxidase stripes of macaque visual area V2, here we show that feedback to the primary visual cortex (V1) is organized into parallel streams resembling the reciprocal feedforward pathways. This suggests that functionally-specialized V2 feedback channels modulate V1 responses to specific stimulus attributes, an organizational principle potentially extending to feedback pathways in other sensory systems.
Highlights
The sensory neocortex consists of hierarchically-organized areas reciprocally connected via feedforward and feedback circuits
Neuronal receptive fields (RFs) in higherorder areas become tuned to increasingly complex stimulus features, with multiple parallel pathways specialized in processing specific attributes of sensory stimuli
In this work, using selective viral-mediated labeling of FB connections arising from specific V2 CO stripes, we show that, like V1-to-V2 FF pathways, V2 FB connections to V1 are organized into multiple parallel streams that segregate within the CO compartments of V1 and V2
Summary
The sensory neocortex consists of hierarchically-organized areas reciprocally connected via feedforward and feedback circuits. Using viral-mediated labeling of feedback connections arising from specific cytochrome-oxidase stripes of macaque visual area V2, here we show that feedback to the primary visual cortex (V1) is organized into parallel streams resembling the reciprocal feedforward pathways This suggests that functionally-specialized V2 feedback channels modulate V1 responses to specific stimulus attributes, an organizational principle potentially extending to feedback pathways in other sensory systems. These projections arise predominantly from V1 layers (L) 2/3 and 4B, and sparsely from 4A and 5/6, with L4B projecting more heavily to thick stripes compared to other stripe types[23,24] It is debated whether V2-to-V1 FB connections form similar parallel pathways that segregate within V1 CO compartments[25,26,27], maintaining stream specificity, or diffusely project to all compartments[28], integrating information across streams.
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