Layer 3 dynamically coordinates columnar activity during spatial integration in mouse V1

Abstract

To establish useful representations of the environment, primary visual cortex (V1) integrates inputs from various spatial locations. Spatial integration is a fundamental, context-dependent neural operation involving extensive neural circuits that span across all cortical layers of a V1 column and reflects both feedforward and feedback processing. How spatial integration is dynamically coordinated across cortical layers remains poorly understood. We recorded single- and multi-unit activity and local field potentials across V1 layers of awake mice while they viewed stimuli of varying size, and used dynamic Bayesian model comparisons to identify when laminar activity and inter-laminar functional interactions showed surround suppression, the hallmark of spatial integration. We found that surround suppression is strongest in layer 3 (L3) and L4, where suppression is established within ~10 ms after response onset, and that receptive fields dynamically sharpen while suppression strength increases. Importantly, we also found that specific inter-laminar functional connections resembled a surround-suppressed tuning curve, parametrically driving target layers depending on stimulus context. Taken together our results shed light on how L3 dynamically coordinates activity across a cortical column and on the different functional roles of cortical layers in spatial integration.