Figure 1. Orderly coordination of constituent movements during reach and grasp to drink (RGD).
(A) Schematic of a head-restrained mouse reaching with its left hand for a waterspout positioned randomly at one of five locations (ipsilateral P1, P2; central P3; contralateral P4, P5).
(B) Schematic of the serial order of RGD and its constituent movements. RGD involves four components: reach, grasp, withdraw and hand lick. The reach consists of hand lifting, aiming, and advancing to target; the grasp opens and closes the digits at the target; the withdraw supinates the hand to the mouth and opens the digits to enable water licking. The color code is used in all subsequent figures.
(C) Example hand trajectory annotated with constituent actions. The dashed line indicates the reference direction in relation to target; +, waterspout location.
(D) Spatial contour map of hand location from side view at lift, aim and advance endpoint. Contours indicate probability starting from 0.01/mm2 with equal increment of 0.01/mm2; 6229 trials from 70 sessions in 25 mice across five target locations; +, waterspout location.
(E) Hand position relative to target at the advance endpoint (median ± interquartile range). Zero means digits are located at the waterspout. Kruskal-Wallis test with Tukey’s post hoc test, χ2 = 40.74, p = 1.18e-05. Horizontal lines in boxplots indicate 75%, 50%, and 25% percentile. Whiskers represent data point span to 90% or 10% percentile. Data from 70 sessions from 25 mice. The same animals were used in the following figure panels.
(F) Top: Hand postures at lift (fingers slightly closed and flexed), aim (palm rotated toward target), advance endpoint (fingers extend and open for grasp) and hand-lick (hand can be closed or open). Bottom: Distribution of hand rotation score as a reflection of palm-facing direction. Data from 6229 lifts, aims, advance endpoints; and 119584 licks from 70 sessions in 25 mice. Note the near 180-degree hand supination from reach-grasp (pronated) to withdraw-lick (supinated).
(G) Movement profiles of an example trial from lift onset to first hand lick. Annotated lift, aim, advance, grasp/withdraw are color coded. Dashed lines indicate z-score normalized zeros for each movement variable. Arrows point to two separate hand speed accelerations that reflect movement adjustments during reaching.
(H) Example of annotated hand trajectories of three random trials for each position in the same session.
(I) Movement duration from lift to grasp for the five target locations. Two-tailed nonparametric Kruskal-Wallis test, statistic χ2 = 91.07, p = 7.78e-19.
(J) Distance from aim to target for the five locations. Kruskal-Wallis test, χ2 = 100.02, p = 9.72e-21.
(K) Distributions of the temporal occurrence of lift and first lick relative to time of waterspout contact for the 5 waterspout locations. Median lift-to-contact duration for P1 -P5: 179.2, 158.3, 195.8, 320.5, 379.2 msec; data from 1167, 1199, 1136, 1121, 1077 trials of 70 sessions from 25 mice.