Layer-specific profiles of factual and counterfactual feedback signals in human early visual cortex during navigation – 7T fMRI study

Abstract

We rely on pre-existing models of the world stored from past experiences in order to form internal representations of our present environment. In addition to facilitating perception in the present, these models enable us to engage in prospective thoughts and mental simulations unrelated to the immediate environment, known as counterfactual thoughts. Traces of both streams have been found to share some neuronal mechanisms at the earliest level of cortical processing (Monaco, 2020; Huang, 2021). It is still a challenge to understand the mechanisms that allow the parallel existence of these two streams of thought while at the same time keeping the perception of reality and imagination segregated. We used a VR headset to familiarise participants with a virtual environment prior to scanning. We recorded 7T fMRI while participants were presented with videos simulating navigation through the environment. Directional cues elicited expectations for an upcoming room that the participant was not presently viewing, but about which they could generate prospective thoughts. The lower right quadrant of the video was hidden behind an occluder, blocking feedforward input to the corresponding patch of the visual cortex. We applied MVPA analysis to probe the contents of the activation in the non-stimulated areas of V1 and V2. The results revealed that different top-down inputs target different cortical layers depending on the type of information they carry. Our data suggests the coexistence of information streams might depend on cortical layering, and layer-spanning pyramidal neurons that integrate feedforward and feedback processing (Larkum, 2018).