Fig. 1: Action potential propagation speeds systematically vary around the human fovea centralis.
From: Synchronization of visual perception within the human fovea
a, Sample preparation (cross, fovea; ellipse, optic disc). b, Beta-III-tubulin-immunolabeled foveal explant post-HD-MEA recording. The hole in the central fovea resulted from tissue removal after HD-MEA recordings. Small circle, foveola; large circle, fovea. c, Top: successive frames of AP waveform video of an RGC axon, 1.4–2.05 ms postinitiation. Color—waveform amplitude. Bottom left: average AP waveform at increasing distances from the soma (yellow squares). Red square, waveform trough. Bottom right: linear regression (dashed line) of travel time versus distance. d, Top: electrical images of representative foveal RGCs. Bottom: composite image of 18 representative RGCs. e, Top: estimated RGC axon trajectories for one preparation. Three axons are accentuated (black arrows). Small circle, umbo (magnified below); large circle, foveola. Inset: cone-to-RGC connectivity in the umbo with adjacent cones (orange discs) and target RGCs (gray discs). f, Somatic location of 1135 RGCs (11 explants). Color—axonal propagation speeds; radial lines, 30° bins. g, Axonal propagation speed (mean ± s.e.m.) of RGCs within the angular bins from f. Red line, best-fitting sinusoid. Significant difference (Kruskal–Wallis test, ***P < 0.001) between −165° (0.67 ± 0.02 m s−1) and 15° (0.48 ± 0.01 m s−1). T and N regions are indicated by gray bars. h, Comparison of axonal propagation speeds between T (dark gray) and N (light gray) foveal RGCs. Median speeds—T, 0.53 m s−1 and N, 0.48 m s−1 (two-sided Wilcoxon rank-sum test, ***P < 0.001). Data from g replotted by spatial bin. i, Schematic of light stimulation with AOSLO. j, Locations of light stimulation in the foveola (using AOSLO) relative to the CDC in one participant. Radial lines, 30° bins. k, Reaction times (mean ± s.e.m.) for trials in j. No significant differences between angular bins (Kruskal–Wallis test; smallest P values—large spot, P = 0.25; small spot, P = 0.99). T and N regions are indicated by gray bars. l, Normalized reaction times in all seven participants (two-sided Wilcoxon rank-sum test; large spot—NS, P = 0.34 and small spot—NS, P = 0.13). S, superior; N, nasal; I, inferior, T, temporal; Norm., normalized.
