Serial Reversal Learning in an Olfactory Discrimination Task in 3xTg-AD Mice

Male and female 3xTg-AD mice and their B6129F2/J wildtype controls, between 5 and 24 months of age, were tested on a series of 18 olfactory discrimination and reversal tasks in an operant olfactometer. All mice learned the odour discriminations and reversals to a criterion of 85% correct, but the 3xTg-AD mice made fewer errors than the B6129F2/J mice in the odour discriminations and in the first six reversal learning tasks. Many mice showed evidence of near errorless learning and on the reversal tasks, the 3xTg-AD mice showed more instances of near errorless learning than the B6129F2/J mice. There was no evidence of an age effect on odour discrimination, but there was a decrease in errorless reversal learning in aged B6129F2/J mice. In long-term memory tests there was an increase in number of errors made, but no genotype difference. The high level of performance indicates that the mice were able to develop a learning-to-learn strategy. The finding that the 3xTg-AD mice out-performed their littermate controls provides an example of paradoxical functional facilitation in these mice.