Different representations in layer 2/3 and layer 5 excitatory neurons of the primary visual cortex

Abstract

The cortex contains multiple types of excitatory neuron, differentiated primarily by their layer of residence. We recorded from neuronal populations in the mouse visual cortex using 2-photon calcium imaging or Neuropixels probes, and found that excitatory neurons in layer 2/3 (L2/3) and layer 5 (L5) differed in their encoding of visual vs. nonvisual signals, with L2/3 more strongly modulated by visual stimuli and L5 more strongly modulated by movement. Movement had opposite effects on population synchrony in the two layers: it desynchronizes L2/3, by abolishing spontaneous synchronous fluctuations that entrain that population, and synchronizes L5, where excitatory cells are less entrained by spontaneous synchronous fluctuations and more strongly correlated with movement itself. Spontaneous activity was lower-dimensional in L2/3 than L5, with L2/3 population activity dominated by a single dimension of overlap between spontaneous and stimulus-evoked subspaces. We conclude that excitatory neurons in different layers of the visual cortex carry different representations of visual and non-visual signals.