Mouse reach-to-grab task training protocol

It is quite often that animal training may not go as smoothly as described here or in literature. Mice might naturally lick off pellets instead of reaching for them, or not go to the back of the box or stay there. Some would simply exclude the mice from the protocol, but we chose to control the protocol manually and modify the protocol based on observed behaviors.

Training environment is key to a successful training: • Behavioral room should be quite with proper temperature and lighting. • There should be only the one experimenter in the room. The experimenter shouldn’t wear any kind of perfume. • If a mouse jumps out of the hand during habituation to the experimenter, it can be returned to the home cage. The habituation can be tired again after habituating the rest of the mice.

Tips to engage animals into training:

• On shaping day 1, if the mouse shows no interest in getting food (no licks, no reaches), you can try to provide sugar pellets in the home cage with regular chow at the end of day, but still maintain the same total amount of food provided (e.g. 2g of chow + 2g of sugar pellets can be provided for calculated 4 g food daily. Make sure to add an additional shaping day. • During the initial days of training, if the mouse starts biting on the slit or performs more than 20 consecutive in-vain reaches, a brief noise can be introduced by gently scratching the top corner of the side wall. This will distract the mouse and move it to the rear of the reaching box. We have noticed that the mouse would then come forward again after hearing the rotating disk. • If the mouse stays in the back of the test box for more than 5 seconds, rotate the disk again. The sound of the rotating disk might encourage the mouse to come forward. • At the beginning of single-pellet training, if the mouse sniffs through the slit but does not reach, adding a small pile of pellets in the center of the disk encourages the mouse to reach.

Tips to encourage reaching and prevent licking:

• If the mouse attempts to lick off the pellets during the early days of training, move the disk slightly away from the slit. This will prevent the pellet from being reachable by tongue but still reachable by paw. In case the mouse stops licking for a full session, move the disk closer to the slit in the next session. Move 1 to 2 mm closer every 5 minutes, as long as the mouse keeps reaching, until you can place it at the standard 5 mm distance from the front wall. • If the mouse loses too much weight (i.e. < 75% of baseline body weight), it has a tendency to start licking, even after the shaping phase. If the previous solution to licking does not work, we found it helpful to increase the food portion after the session and move back to the shaping setup on the next session.

Tips to increase success rate:

• We strongly encourage a single experimenter to conduct the habituation and behavioral shaping and training sessions. We noted that animals can stop or reduce reaching when a new experimenter is involved at any stages of the task. For instance, even well trained (i.e., “experts”) mice could stop reaching when additional experimenter assisted with the training. • Shaping and training sessions are expected to be performed at the same time of the day to reduce variabilities due to circadian rhythm. • Successful acquisition of this reaching skills requires daily training for at least consecutive 4 days after the completion of shaping. • We were using a rotating disk for pellet delivery. Some modifications may be considered and can be helpful to increase success rate of reaches, such as slightly increasing depth of wells, adjusting the height of disk, and precisely positioning the food dispenser.