Go, No-Go Olfactory Discrimination task
General Overview
In this task mice are presented with two novel pairs of distinct odors. On each trial, one of the odors is presented at an odor port, followed by the delivery of either a sucrose solution or nothing. Mice initially report to the liquid port on each trial but rapidly come to withhold responding at the liquid port after the odor signal for nothing. During odor discrimination training mice are required to learn a series of 2-odor discrimination problems. Following acquisition of the odor discriminations, the mice begin reversal-learning trials. During these trials the reward contingencies of one of the learned odor pairs are reversed such that the odor that formerly signaled sucrose is now paired with nothing, the odor that formerly signaled nothing is now paired with sucrose. This task allows for the assessment of repeated acquisition of leaning using new information in each test session, and takes advantage of the natural sensory capacities of mice in the use of olfactory information.
Apparatus
Behavioral testing is conducted in specially designed test chambers (15.2 x 15.2 x 15.2 cm) mounted within specially designed sound attenuating shells Behavior is monitored by video cameras and a variety of electronic motion detecting systems. Each chamber is equipped with an odor port through which the mice sample orders, and a water well from which the mice receive a water or sucrose reward. The odor port is a 0.3 cm diameter opening located in the center of the right panel. Behind this port is a small hemicylinder in which odorized air streams can be presented when a mouse nosepokes at the odor port. Odors are delivered through tubing connected to the base of the hemicylinder behind the sampling port. Odors are selected from a set of compounds obtained from
International Flavors and Fragrances, which are classified subjectively into categories. Discrimination problems consisted of odors from different categories
(fruity, spicy, herbal, etc.). These odor compounds are diluted 1:20 in propylene glycol. The set of diluted odors used in the discrimination problems are isolated on a removable cartridge connected to a system of solenoids and flowmeters to allow each odor to be individually delivered to the training chamber. All tubing and valves associated with an odor are dedicated to that odor to prevent any cross-contamination between cues. During odor presentation, a second vacuum line prevents the odor from entering the training chamber. Fluids are delivered to a fluid well located above the odor sampling port.
Procedure
This procedure consists of 3 phases: 1) shaping, 2) odor discrimination training, and 3) reversal learning. During phase 1 mouse are shaped to nosepoke at the odor port to receive a water reward in the fluid well. The mice are gradually

shaped poke their snout in the odor port and to then make a response to the fluid well within 3 sec to receive reward. Mice are given 20 trials per session during shaping and once shaped to this procedure, the second phase of odor discrimination training begins.
During odor discrimination training, the mice are presented with a series of odor problems. Each odor discrimination problem consisted of two odors. One odor signals a positive outcome, indicating that a response at the fluid well will result in delivery of 10% sucrose solution. The other odor signals a negative outcome, indicating that the same response will result in nothing. Trials are signaled to the mouse by illumination of the house lights inside the box. When these lights are on, nosepokes into the odor port results in delivery of the preselected odor cue. The mouse terminates odor sampling by leaving the odor port. The mouse then has 3 sec to make a “go” response at the fluid well. If a response is detected, then fluid is delivered to the well. After a response, fluid remains in the well and the house lights remain on until the mouse leaves the fluid well, then the fluid is removed by activating the drain line, and the lights are extinguished to end the trial. If the mouse does not respond at the fluid well within 3 seconds of exiting the odor port, the trial is counted as a “no-go”, and the light is extinguished. Intertrial intervals are 5 sec after correct responses and
10 sec after incorrect responses. During odor discrimination training mice are required to learn a series of four 2-odor discrimination problems. Mice are given
50 trials per session and once the odor discriminations are learned, training begins on the third phase of reversal learning.
Once the odor problems in phase 2 are acquired, the mice begin the third phase of training. During phase 3, the mice are required to learn a series of reversals. In these trials the contingencies signaled by the odor cues in a single discrimination problem are reversed such that the odor previously associated with outcome 1 is now associated with outcome 2, and the odor previously associated with outcome 2 is now associated with outcome 1. Mice are given 50 trials per session.