Feedforward and feedback interactions between visual cortical areas use different population activity patterns

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", such that feedback signaling does not directly affect activity that is fed forward.

Between-area communication through the lens of within-area neuronal dynamics

“…Furthermore, cognition is believed to arise from distributed computational processes. Even in early sensory areas historically thought of as mostly feedforward, the importance of feedback interactions in sensory processing has started to be exposed (Semedo et al, 2022). Therefore, a natural extension of our work will be the implementation of more complex circuit architectures, starting by the introduction of feedback connections, to provide novel insights into the mechanistic interplay of inheritance and emergence of shared fluctuation across spatial scales.…”

Attention improves information flow between neuronal populations without changing the communication subspace

“…A recent set of studies used recordings from multiple populations of neurons to establish that functional communication between different brain areas in the motor 94 or visual system 50,102 is confined to a subspace of activity that is even lower dimensionally than the activity within each area. Our results are consistent with the proposal that this limited communication subspace is an attractive mechanism for behavioral flexibility.…”

Disentangling the flow of signals between populations of neurons

“…Interpretation of DLAG's latent variables and time delays One might interpret the population activity patterns represented by DLAG's across-area variables as distinct "channels" with which two areas communicate [44]. As with any statistical method, however, interpretation of the features extracted by DLAG is subject to ambiguities, particularly when not all relevant brain areas and neurons are recorded [64].…”

“…The data analyzed here are a subset of those reported in [28], and similar but not identical to the subset used in [39, 43]. Activity in V1 output layers was recorded using a 96 channel Utah array (400 micron inter-electrode spacing, 1 mm length, inserted to a nominal depth of 600 microns; Blackrock, UT).…”

“…If communication were to occur in one direction at a time, then existing dimensionality reduction methods could, in principle, provide further insight into these questions. If two areas were to communicate in both directions concurrently, however, then existing methods would only identify the dominant direction of population-level signal flow [43]. Disentangling the concurrent flow of signals between populations remains a substantial barrier in neuroscience (Fig.…”