Extended Data Fig. 6: Visual stimuli that recruit enhanced facilitating feedback preferentially drive dendritic activity.

a, Semi-sparse expression allows tracing of apical trunks to their parent somata. b, Left, soma and dendrite regions-of-interest. Right, fluorescence from a connected soma and apical dendrite. c, Population average dendritic fluorescence as a function of somatic fluorescence, for six stimulus sizes. Trials sorted by somatic activity level, binned in 5% increments, averaged across cells (n = 57 neurons with receptive fields <20° from stimulus centre, and size tuning (p < 0.01) with preference for 20° gratings). Two-way ANOVA on population data to determine effect of somatic activity, stimulus size, and their interaction on dendritic fluorescence showed a significant effect of stimulus size, F(5,131) = 5.96, p = 5 x 10⁻⁵, and a significant interaction, F(5,131) = 4.74, p = 5 x 10⁻⁴. d, Population average somatic and dendritic calcium fluorescence traces for different stimuli from one somatic activity bin, indicated in panel c. e, Dendritic fluorescence as a function of stimulus size, averaged across neurons after effect of somatic fluorescence is removed on a cell-by-cell basis (residual after subtraction of fit to somatic fluorescence; Methods). One way repeated measures ANOVA on n = 57 neurons shows significant effect of size, F(5,280) = 2.681, p = 0.02. Post-hoc tests show residual at 5° is significantly smaller than residuals at larger stimulus sizes (paired t-tests, p < 0.05). f, Dendritic and somatic size preference. Dendrites prefer larger stimuli as a population (paired t: p = 1 x 10⁻⁶). Data from n = 131 neurons with receptive fields <20° from stimulus centre, significant size tuning (p < 0.01), and preferring 10°,20°, 40° or 60° gratings. Data from 26 sessions in 9 mice. Dendritic preference computed from residuals as in e. g, Schematic illustrating topographically offset feedback facilitating dendritic excitation during global events.