Fig. 4.

Stride swing timing drives interlimb coordination changes. (A) Sample paw angle (teal) and corresponding velocity (grey) traces of one mouse for Trial 1 (top) versus Trial 5 (bottom) and Day 1 of training. Black arrow points to change in paw velocity mid-swing. (B) Sample swing cycle paw angle and velocity curves for non-hover (left) and hover (right). Schematic illustrates quantification of hover time using change in paw angle slope. (C) Histogram of hover time for front (left) and hind (right) paws of all cycles across all animals for Day 1 Trial 1 (top row) and Trial 5 (bottom row) at 20 rpm speed bin. Vertical line indicates hover threshold determined from Trial 1 data. (D) Average proportion of hover cycles and hover time for classified hover cycles in forepaws as a function of training. Proportion of 1 is 100% of cycles in 20 rpm bin. Mean ± SD across animals. Statistical significance was assessed by t-tests comparing Day 1 Trial 1 to each subsequent day and trial. Points with p < 0.05 are indicated by black filled markers. Solid horizontal line denotes mean and dashed line is SEM of animals (N = 7) from Day 1 Trial 1. (E) Schematic showing difference in actual versus extrapolated (if there was no hover) touch-down time between the diagonal paw pair of one cycle. (F) Paw touch-down time difference between extrapolated and actual on Day 1 Trial 1 (left) and Trial 5 (right). Thick horizontal line represents mean of 7 animals. Statistical significance was assessed by t-tests. Extrapolated: 0.14 ± 0.04, actual: 0.13 ± 0.04, p = 0.54. No-hover prediction: 0.15 ± 0.04, actual: 0.08 ± 0.03, p = 0.003. (G) Histogram shows touch-down time difference probabilities of actual (filled) and extrapolated (outlined) times for all cycle data on Day 1 Trial 5. Box plot (right) shows median and spread of touch-down time difference between actual and extrapolated times. Statistical significance was assessed by t-tests. Actual: 0.08 ± 0.005, extrapolated: 0.14 ± 0.006, p < 0.01. A two-sample F-test for equal variances assessed variance of the footfall time differences between actual and extrapolated. ${\sigma }_{\text{actual}}^2=0.007$, ${\sigma }_{\text{extrapolated}}^2=0.01$, F(322,322) > 1, p < 0.01.