Abstract
Brain function relies on the coordination of activity across multiple, recurrently connected brain areas. For instance, sensory information encoded in early sensory areas is relayed to, and further processed by, higher cortical areas and then fed back. However, the way in which feedforward and feedback signaling interact with one another is incompletely understood. Here we investigate this question by leveraging simultaneous neuronal population recordings in early and midlevel visual areas (V1–V2 and V1–V4). Using a dimensionality reduction approach, we find that population interactions are feedforward-dominated shortly after stimulus onset and feedback-dominated during spontaneous activity. The population activity patterns most correlated across areas were distinct during feedforward- and feedback-dominated periods. These results suggest that feedforward and feedback signaling rely on separate “channels”, which allows feedback signals to not directly affect activity that is fed forward.
Highlights
Brain function relies on the coordination of activity across multiple, recurrently connected brain areas
We found that the population activity patterns involved in feedforward signaling were distinct from those involved in feedback signaling
We asked: (1) how the interaction evolved during stimulus presentation and the subsequent period of spontaneous activity; and (2) how the interaction depended on the time delay considered between the two areas
Summary
Brain function relies on the coordination of activity across multiple, recurrently connected brain areas. Other studies have studied feedforward or feedback signaling by measuring activity simultaneously in two areas, and comparing temporal delays in pairwise spiking correlations[16–21] or phase delays in local field potentials (LFP)[22–25] These studies have suggested that feedforward signaling occurs shortly after stimulus onset and that feedback signaling appears later. To understand inter-areal interactions more deeply, it is possible to record activity from large neuronal populations simultaneously in different cortical areas, and characterize what patterns of population activity are most related across those areas[19,26–33] This approach has led to new proposals about how activity can be flexibly routed across brain areas This indicates that activity patterns in V1 that most affect downstream activity during feedforward processing are not the ones most affected by feedback signaling Our results reveal both the dominant direction of signal flow between areas on a moment-by-moment basis and the distinct nature of population activity patterns involved in feedforward and feedback interactions
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