Automated study of simultaneous-cue olfactory discrimination learning in adult mice

Adult C57BL/6J mice were trained in a fully automated operant task to discriminate between 2 simultaneously presented odors for water reward. Each mouse was trained on 16 different discrimination problems to a criterion of 90% correct in a block of 20 trials for each problem. Each of the mice tested reached criterion on all discriminations; the number of errors made before reaching criterion was greatest for the first few problems and decreased substantially thereafter. Acquisition performance on early trials of novel discriminations suggested that mice form learning sets for olfactory cues. The mice were trained on 4 additional problems and tested for memory with probe trials at retention intervals of 1, 2, 4, and 8 weeks. Good retention of olfactory cues was seen even at the longest memory delay. Automated testing of olfactory discriminations should be useful for assessing learning and memory abilities in genetically modified mice.