Figure 3. Combined synaptic input from the local L2/3 cortical network matches the RF structure of the receiving neuron.

a, Top left, presynaptic RF outlines overlaid in normalized visual space (after rotation, translation and scaling of the postsynaptic RF; see text, Methods and Extended Data Fig. 7). Red outline indicates an ON subfield, blue outline indicates an OFF subfield. Bottom left, superimposed RF outlines for neurons assessed presynaptically, but which did not connect. Top middle, sum of presynaptic RFs. Each presynaptic RF was weighted by the EPSP amplitude from the pre- to the postsynaptic neuron. Bottom middle, RF sum for unconnected neurons assessed presynaptically. Top right, RF sum of the postsynaptic neurons. Before summing, each postsynaptic RF was weighted by the EPSP amplitude from the presynaptic to the postsynaptic neuron. b, Each point indicates the correlation between the presynaptic RF sum (weighted by the EPSP amplitude) and the corresponding postsynaptic RF sum, when including only connections in quarters of the connection amplitude distribution. The RF sum of the strongest 25% of inputs has the highest correlation with the postsynaptic RF (R = 0.67). This correlation value falls with decreasing connection strength. Disc area and values above represent the total synaptic weight accounted for by each quarter of the connection amplitude distribution. c, Relationship between ON and OFF subfields of connected pre- and postsynaptic neurons, ranked and displayed according to EPSP amplitude. Left column, presynaptic RF outlines of neurons grouped in quarters ranked by decreasing EPSP amplitude. Middle-left and middle columns, sum of binarized presynaptic ON and OFF subfields, respectively. Middle-right column, subtraction of summed OFF from summed ON subfields for presynaptic neurons. Right column, subtraction of summed OFF from summed ON subfields for postsynaptic neurons.