Fig. 3: Periodic gait cycles in freely moving rats and mice.

a, Trajectories in the freely moving rat of the normalized x position (Px) as a function of time (mean ± s.d. of 1,000 propagations through the probabilistic model) for the left wrist (purple), right wrist (red), left ankle (cyan) and right ankle (yellow) joint during gait. Schematic above at left illustrates the normalized position of an ankle joint (cyan spot) and normalization joint (magenta). Individual traces show the estimated position (solid line) with the uncertainty in the position represented by the width of the surrounding shaded area. Note that the left and right wrist joints were occluded for large parts of this segment, illustrated by the larger uncertainty in position on these traces. b, As in a, but for data from a freely moving mouse. All joints are clearly visible throughout the mouse segment, resulting in small uncertainty ranges for all traces. c, Autocorrelations of the normalized x position for data from a freely moving rat as a function of time (left) for four different limbs as well as a corresponding model fit via a damped sinusoid (black). Fourier-transformed autocorrelations of all limbs (right) have their maximum peak at the same frequency. Colors as in a. d, As in c, but for data from a freely moving mouse. e, Population-averaged trajectories of the normalized x position for data from freely moving rats as a function of time for the ACM (left), the naive skeleton model (center) and the surface model (right). Individual traces represent mean and s.d. Data from 28 sequences, 146.5 s, 58,600 frames in total from four cameras, n = 2 rats. Colors as in a. Trajectories of the ACM and the naive skeleton model correspond to the 3D joint locations, whereas trajectories of the surface model correspond to the 3D locations of the associated surface markers. Scale bar on left applies to both left and center. f, As in e, but for data from freely moving mice. Data from 29 sequences, 93.8 s, 73,536 frames total from four cameras, n = 2 mice. Scale bar on left applies to both left and center.