(A) Relationship between retinotopic alignment of LGN and L4 SIN RF centers (x-axis) and (1) the efficacy of the connection between concentric LGN neurons and SINs (filled circles, y-axis, left side) and (2) the percent connected cell pairs (solid line, y-axis right side). The proportion of connected pairs is high (~73%) when alignment is good (i.e. when the distance between thalamic and cortical RF centers is less than 1/2 the diameter of the LGN RF), and drops off precipitously as misalignment increases. Non-connected cell pairs were ascribed an efficacy of ‘0’ and are shown by open circles. Insets show cross-correlograms for four LGN-SIN pairs with different degrees of RF alignment. Red arrow denotes the data point for cell pair shown in B-E. (B-E) Importantly, LGN-SIN synaptic connectivity does not depend on similarity of RF properties other than alignment. An example of connected cell pair with dissimilar RF sign (LGN cell was OFF-center, SIN was ON-dominated) and dissimilar sustained/transient cell class. (B) Spatial RF maps from a LGN neuron and a retinotopically-aligned L4 SIN. (C) LGN and SIN RFs are dissimilar in their RF sign. The LGN neuron yields only an OFF response at short latencies, and SIN yields earlier and stronger ON response. (D) These LGN and SIN RFs are also dissimilar in their sustained/transient responses. PSTHs of the responses of the LGN cell (upper) and the SIN (lower) to an optimal stationary stimulus placed over the RF center, presented for two seconds (arrows mark stimulus onset). The LGN cell responded in a purely transient manner, but the SIN’s response had both transient and sustained components and was therefore classified as a ‘sustained’ cell (Bezdudnaya et al., 2006; Stoelzel et al., 2008; Zhuang et al., 2013). (E) Cross-correlation of the spike trains (spontaneous spikes only) of the LGN cell and the SIN, indicating synaptic connectivity.