Fig. 5
From: Top-down feedback controls spatial summation and response amplitude in primate visual cortex
Effects on spatial summation of inactivating feedback connections in a recurrent network model of V1. a The model architecture. Connection types are color coded according to legend. Pink and black boxes: population of layer 2/3 inhibitory (I) and excitatory (E) cells, respectively, labeled according to the position of their RFs relative to that of the cells in the center recorded V1 column; accordingly, Ectr/Ictr are the cells in the center column, and Enear,far/Inear,far those in the near and far surround, respectively. The proximal surround, as defined in this study, encompasses the near surround (which is coextensive with the spatial spread of V1 horizontal connections) and the more proximal region of the far surround, while the distal surround encompasses the more distal region of the far surround (coextensive with the full extent of feedback connections). FF: excitatory feedforward afferents from other V1 layers to layers 2/3; EFB: excitatory feedback connections from a single extrastriate area to V1. Icons at the bottom and in panel (c); RF and surround components, with red areas indicating regions activated by a stimulus of increasing diameter. b Firing rate of the local E and I cells in the model, plotted against the input current. c Size tuning curves of the model Ectr and Ictr neurons with intact feedback and with different levels of feedback inactivation, as per legend. d–g Data-model comparison. Model results were computed by multiplying feedback weights by 0.5 (50% reduction in feedback activity). d Comparison of sRF size in the data (left) and in the model (right). e Normalized spike-rates measured at the peak of the size tuning curves with and without feedback inactivation, in the data (left) and in the model (right). Both the data and model responses were normalized to the response at the peak of the size tuning curve with feedback inactivated. f Suppression Index (SI) in the data (left) and model (right) for stimuli extending into the proximal surround, measured as described for Fig. 3b. g Normalized spike-rates with and without feedback inactivation measured at stimulus sizes corresponding to the peak of the size tuning curve with intact feedback. Both the data and model responses were normalized to. the response at the peak of the size tuning curve measured with intact feedback
