Optimization of the touchscreen paired-associate learning (PAL) task for mice and its dorsal hippocampal dependency

Two versions of the touchscreen paired-associate learning (PAL) task have been developed for rodents: same PAL (sPAL) and different PAL (dPAL). These tasks are very important in studying murine models of Alzheimer’s disease and schizophrenia, and have also been used to test object-location memory in various studies. However, the relatively long time needed for the tasks (approx. 50 days for mice) limits their widespread use. By giving training that was more intensive with a higher number of trials, we shortened the time required for learning saturation in sPAL and dPAL to about one-third of the time required for the generally used protocol. Furthermore, by applying a reduced number of objects and trial types for sPAL, we developed a simplified version of sPAL, termed 2-object sPAL, in which mice could reach the fully learned level in 6 days. Our pharmacological experiments indicate that the dorsal hippocampal CA1 region is crucial for the performance of the two PAL tasks with the new protocols and the new 2-object sPAL. This work has significantly enhanced the usefulness of the touchscreen PAL tasks to increase the speed of learning, but they remain highly hippocampus-dependent object-location memory tasks.