Extended Data Fig. 3: Action potential propagation speed and axon diameter along RGC axons.
From: Synchronization of visual perception within the human fovea
a, Histogram of normalized, local action potential propagation speed measurements. b, Density-colored scatter plot of normalized propagation speed values (20,824 speed measurements along 2,558 axons from 34 retinal explants). Each point represents the local action potential speed measured along short (usually <35 µm) axonal segments. Orange line: mean normalized speed. Black brackets (top): statistical comparisons between consecutive 0.4 mm bins, starting 0.2 mm away from the soma. Although the first test was significant (two-sided Wilcoxon rank-sum test, ***P < 0.001), the effect size was small (~5% speed increase; first bin: 0.98 ± 0.23; second bin: 1.03 ± 0.24; mean ± s.d.). c, Schematic of the RGC axon labeling procedure by injection of a current. Panel c is created with BioRender.com. d, Example of a labeled RGC axon across 12 FOVs. e, Three example FOVs (5, 7, 11 in d) at increasing distance from injection site. Scale bar: 10 µm. Images from one axon, representative of seven axons from three retinae. f, RGC axon segment in one field of view (~400 µm distance from injection site). White: intensity profiles and FWHM estimates measured at three sampling points along an axon segment. Representative of the axon shown in d and e. g, Same field of view as f. Left: example of two consecutive varicosities (white triangles). Intensity profile is measured between the varicosities. Right: diameter of the IVS estimated as FWHM of the average intensity profile (red) between two consecutive varicosities. h, Successive IVS diameter measurements as a function of distance from the injection site. Points are color-coded according to normSNR of the field of view. Data are from the same axon shown in d–g, with multiple IVS measurements per field of view. i, Weighted histogram showing the distribution of measured diameters for the same axon shown in d–h. Solid line: kernel density estimate. N refers to the number of IVS diameter measurements (individual points shown in h). j, Average normalized diameter at increasing distance from the injection site. Histogram includes 368 pooled IVS diameter measurements from seven RGC axons across three retinae. k, normSNR-colored scatter plot of normalized IVS diameter values (same data as in j). Dashed line: unity.
