Differential tuning and population dynamics of excitatory and inhibitory neurons reflect differences in local intracortical connectivity

Neuronal responses during sensory processing are influenced both by the organization of intracortical connections and the statistical features of sensory stimuli. How these intrinsic and extrinsic factors govern activity of excitatory and inhibitory populations is unclear. Using two-photon calcium imaging in vivo and intracellular recordings in vitro, we investigated the dependencies between synaptic connectivity, feature selectivity and network activity in pyramidal cells (PCs) and parvalbumin-expressing fast-spiking (PV/FS) interneurons in mouse visual cortex. In PC populations, patterns of neuronal correlations were largely stimulus-dependent, indicating that their responses were not strongly dominated by functionally biased recurrent connectivity. In contrast, visual stimulation only weakly modified co-activation patterns of PV/FS cells, consistent with the observation that these broadly tuned interneurons received very dense and strong synaptic input from nearby PCs with diverse feature selectivities. Therefore feedforward and recurrent network influences determine the activity of excitatory and inhibitory ensembles in fundamentally different ways.