Different representations in layer 2/3 and layer 5 excitatory neurons of the primary visual cortex
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 excita-tory neurons in layer 2/3 (L2/3) and layer 5 (L5) differ 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 has opposite effects on population synchrony in the two layers, desynchronizing L2/3 by abolishing spontaneous population oscillations, and synchronizing L5, where excitatory cells are less entrained by oscillation and more strongly correlated with movement itself. Spontaneous activity is 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 the population code of in different layers of the visual cortex differentially balances visual and non-visual signals.