Mathematical Biology Seminar Gregory Handy, University of Minnesota, Tueday, April 22, 2025 2:00pm in LCB 215 Ensemble Dynamics in Visual Cortex: Probing the Spatial and Feature Dependencies of Recurrent Activity Abstract: Although most synapses within the neocortex are recurrent, the functional impact of this recurrence remains unclear. Prior experimental and theoretical work in the primary visual cortex (V1) suggests that recurrent excitation amplifies responses when signals are weak to optimize detection, while recurrent inhibition suppresses responses when signals are strong to optimize discrimination. Deepening our understanding of the logic for when recurrent activity facilitates cooperation among cortical ensembles and when it mediates competition beyond these initial results is fundamental to understanding cortical computation. To isolate the impact of local recurrence, we used multiphoton holographic optogenetics to activate neuron ensembles in V1 without external stimuli. We found that both the spatial arrangement and stimulus preference of the ensemble shape the activity response, with the strongest effects within 30 µm of a stimulated cell. Compact, co-tuned ensembles recruit nearby iso-tuned neurons while suppressing others. Computational modeling reveals that local excitatory connections and selective inhibition explain these patterns, highlighting a trade-off between excitatory and suppressive pathways. This combination of in vivo and in silico circuit interrogation explains how recurrent cortical circuits selectively amplify or suppress cortical activity depending on the precise pattern of co-active neurons.