Fig. 8: Modeling suppression of RGC excitatory responses through electrical isolation of inhibition in the BC axonal arbor.
a Example histogram of CSR value measured at each of the BC ribbon output synapses when activating a single inhibitory synapse in the active compartmental cable model of the BC (see Fig. 7d). Q1 indicates the quartile of ribbons with the lowest CSR values, and Q4 indicates the quartile of ribbons with the largest CSR values. b Difference of Gaussian receptive field when using the average Q1 CSR value (left) or the average Q4 CSR value (right). Note: Center size and surround size were fixed at values obtained when fitting to PixON excitatory conductances (see Fig. 4c and “Methods”). c BC receptive field model of RGC excitation, which predicts RGC excitatory responses as the sum of BC receptive field subunits (difference of Gaussian receptive fields from (b)) sampled across the RGC dendritic arbor (see Fig. 4a and “Methods”). d RGC excitatory conductances for a range of spot sizes predicted by the BC receptive field model (dotted line) and experimentally measured (solid line). Left shows the RGC excitatory responses predicted when providing the model with PixON RGC dendritic arbors and a BC subunit receptive field with a CSR value of 1.1 (Q1 average from (a)). Right shows the RGC excitatory responses predicted when providing the model with ON alpha RGC dendritic arbors and a BC subunit receptive field with a CSR value of 2.3 (Q4 average from (a)). e, f Average surround suppression of PixON excitatory responses plotted against average surround suppression of ON alpha excitatory responses. Dots indicate values predicted from the BC receptive field model with PixON surround suppression predicted using the average Q1 CSR values, and ON alpha surround suppression predicted using the average Q4 CSR values. Note: Each dot represents a separate simulation in which a unique set of inhibitory synapses were simultaneously activated. The red cross indicates the average surround suppression of excitatory conductances experimentally measured in the PixON RGCs (81% ± 3.7%, n = 14) and the ON alpha RGCs (28% ± 3.1%, n = 8). The length of the cross lines indicates the standard error of the mean. Predictions were made with CSR values obtained when activating one inhibitory synapse (left), 60 inhibitory synapses (middle), or all 120 inhibitory synapses (right). For (e), CSR values were obtained from the passive compartmental cable model of the BC. For (f), CSR values were obtained from the active model of the T6 BC. Source data are provided as a Source Data file.
