Operant conditioning in the Ts65Dn mouse: learning.

Ts65Dn and littermate controls were trained to respond (nose-poke) under operant schedules of reinforcement. A small difference was observed in the initial operant training of the Ts65Dn mouse that disappeared with training under a fixed-ratio 15 schedule of milk presentation. No difference was observed in a position reversal task in which mice initially trained to respond upon one photocell had to learn to respond on a previously inactive photocell. Under an incremental repeated acquisition of behavioral chains schedule, no difference was observed when one or two responses were required to complete the sequence. However, when three or four responses were required to complete the sequence, a marked deficit was observed in the Ts65Dn mice. These results show that both Ts65Dn and littermate controls can be trained to respond under operant schedules of reinforcement, but that Ts65Dn mice have a learning deficit that is correlated with task difficulty.