Figure 1. Gustatory stop-signal task in head-restrained mice. a, Schematic of the apparatus for the gustatory stop-signal task. Inset shows the custom-made multibarrel lick spout with the individual barrels aligned and encased in dental cement to form a small well capable of holding ∼2 μl of preformed stimuli. A fan above the lick spout is used to eliminate any potential olfactory cues from the taste stimuli. A small air-puff valve is placed near the whiskers for task reinforcement during stop-trial errors. b, Schematic of the general structure of the gustatory stop-signal task. Before moving into licking position, an ∼2 μl stimulus is preformed in the well of the lick spout tip. After moving into lick position, a brief tone is played to alert mice that a trial has begun. After the tone, mice have 3 s to decide to participate in a trial by initiating licking; otherwise, the lick spout retracts and is cleaned with a 20 s time-out period ensuing. After the first lick is registered on a trial, mice enter a 700 ms decision phase (light gray box) during which they must choose to continue or stop licking the lick spout depending on the stimulus quality (see Table 1 for stop and no-stop stimuli). Mice then enter a reward/punishment phase (dark gray box) depending on the trial type and performance during the preceding decision phase. c, Specific trial types and outcomes of the gustatory stop-signal task. Trial types are separated into stop and no-stop, with correct and error outcomes for both types. On correct-stop trials, mice must stop licking before reaching six licks after stimulus contact to avoid punishment. On stop-trial errors, mice fail to stop licking and reach at least six licks in the decision phase, causing a light air puff to the whiskers, spout retraction, and a 20 s time-out punishment. On correct no-stop trials, mice must reach ≥6 licks in the 700 ms decision phase to then move into the reward phase during which they must execute an additional 2 licks in 500 ms (8 licks total) to receive an extra ∼2 μl drop of sucrose for consumption. On no-stop trial errors, mice fail to reach six licks in the 700 ms decision phase, causing spout retraction and a 20 s time-out punishment. d, Raster plot of licks during a full example session in a well trained mouse, with trial type and outcome aligned to each trial. To see the difference in behavior during different trial types clearly, the first 100 correct stop and no-stop trials were plotted separately, with each trial aligned by the first lick. Note the clear change in licking behavior during stop trials and the consistent unabated licking during correct no-stop trials.