Abstract
Visual stimuli evoke fast-evolving activity patterns that are distributed across multiple cortical areas. These areas are hierarchically structured, as indicated by their anatomical projections, but how large-scale feedforward and feedback streams are functionally organized in this system remains an important missing clue to understanding cortical processing. By analyzing visual evoked responses in laminar recordings from 6 cortical areas in awake mice, we uncovered a dominant feedforward network with scale-free interactions in the time domain. In addition, we established the simultaneous presence of a gamma band feedforward and 2 low frequency feedback networks, each with a distinct laminar functional connectivity profile, frequency spectrum, temporal dynamics, and functional hierarchy. We could identify distinct roles for each of these 4 processing streams, by leveraging stimulus contrast effects, analyzing receptive field (RF) convergency along functional interactions, and determining relationships to spiking activity. Our results support a dynamic dual counterstream view of hierarchical processing and provide new insight into how separate functional streams can simultaneously and dynamically support visual processes.
Highlights
Visual processes exhibit complex patterns of fast-evolving activity that are distributed across cortex
We established the simultaneous presence of a gamma band feedforward and 2 low frequency feedback networks, each with a distinct laminar functional connectivity profile, frequency spectrum, temporal dynamics, and functional hierarchy
The overall interaction strengths quickly and transiently increased across the frequency spectrum (Fig 1D). This was followed by sustained interactions in the beta and low gamma band, with a narrowband power reduction around 60 Hz [24,25]
Summary
Visual processes exhibit complex patterns of fast-evolving activity that are distributed across cortex. Within 100 ms after stimulus onset, activity spreads throughout visual cortex and beyond, both in primates and rodents [1,2], enabling functional cortico–cortical interactions that are necessary for even the most elementary visual operations [3,4]. Such networked processing occurs over dense anatomical projections that reciprocally connect cortical areas. Understanding how visual cortex enables fast, distributed processing over its fixed hierarchical structure may provide important clues to further understanding large-scale cortical function. Based on onset latencies after stimulation, it was shown that the feedforward spread of activity from
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