How orientation-tuned neurons connect to other orientation-tuned neurons remains controversial10,35. Some measurements suggest that individual neurons sample heterogeneous input, from neurons with diverse orientation-tuning10. Models indicate that specific connectivity is not required for orientation tuning36. However, other measurements emphasize that neurons prefer to make synapses with neurons sharing similar orientation tuning35, but orientation tuning at the level of subthreshold membrane potential is weak37,38. We thus compared the orientation tuning of populations of individual spines and the output of their parent neuron. We identified neurons with tuned output (OSI, 0.91 ± 0.04, n=5) (Fig. 5a) and measured the orientation tuning of large numbers of dendritic spines per neuron (average, 201 spines; range, 120-298 spines) (Fig. 5b-d). Contributions to the signal from back-propagating action potentials were removed using a computational subtraction procedure (Methods; Supplementary Fig. 11). For individual neurons, the orientation tuning averaged across all spines was biased towards the orientation tuning of the parent neurons (Fig. 5e, f) (p < 0.01, Wilcoxon rank sum test), although the modulation depth for spines was smaller (p < 0.01, Wilcoxon rank sum test). A
