Figure 2.

Head-Restrained Mice Can Reach for Water in Different Directions, Guided by the Olfactory System

(A) Top-view schematics of a head-fixed mouse trained to reach toward three different locations using a motorized system to automatically move the water spout in space (left, center, and right targets). Example reconstructions of the paw trajectories to each target during one session of a proficient mouse are depicted with thin colored traces, and the average trajectory is depicted with a thicker line.

(B) On the left, performance of directional reaching across training sessions (n = 19 mice). Trials are considered “rewarded” when the water droplet is retrieved from the water spout within 7 s from its presentation. Droplet retrieval was measured with an IR beam break detector. Mice attained plateau performance after three training sessions (^∗p < 0.01, Tukey post hoc test, compared with the first session and p > 0.01, RM ANOVA, compared with the last session). On the right, reaction time across sessions for the three directions tested. Reaction time was computed between the droplet presentation time and the first release of the resting bar.

(C) Map of the reaching space. Top-view schematics of a mouse reaching to 1 of 46 possible reward positions. The water presentation locations are disposed on a radial grid around the mouse snout spanning from level 0 (closest to the mouse) to level 5 (farthest from the mouse) (L0–L5). The color of each position represents the percentage of reached trials averaged across six mice (median). A trial was considered “reached” if the mouse touched the water spout within 10 s from water drop presentation.

(D and E) Perturbation of different sensory modalities in the three-directional reaching task shows that the chemosensory system is essential for the performance (rewarded trials, D) and detection (reaction time, E) of the water drops. The role of light (“No light,” n = 6 mice; p = 0.37, paired t test for performance, and p = 0.16, Wilcoxon signed rank test for reaction time), sound (“White noise,” n = 5 mice, p = 0.76 for performance and p = 0.05, paired t test for reaction time) and air perturbation (“Air suction,” n = 7 mice, p < 0.01 for performance and p < 0.01, paired t test for reaction time) was tested on a trial-by-trial basis within session. The role of whiskers (“Whiskers trimming,” n = 6 mice, p = 0.837 for performance and p = 0.04, paired t test for reaction time) and olfactory system (“olfactory lesion,” n = 5 mice, p < 0.01 for performance and p < 0.01, paired t test for reaction time) was tested in separate sessions, before and after the treatment. Single mouse performance and timings are represented by light gray lines. Mean across mice in black. ^∗p < 0.001.

(F) Top-view pictures of the snout of a representative mouse in the directional reaching task during water drop presentation in the left (green), center (yellow), and right (pink) position. Upon water delivery, mice direct the tip of the nose toward the reward.

(G) Snout tip video tracking (Experimental Procedures) showed that mice orient the snout toward the reward (n = 4 mice). Individual traces show the average nose displacement of each mouse for the three reward locations. The data are aligned to the time of reward presentation (dotted line).