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

Abstract

Two versions of the touchscreen paired-associate learning (PAL) task have been developed for rodents: same PAL (sPAL) and different PAL (dPAL). These tasks have been used to test object-location memory in different studies, and are also crucial in studying murine models of Alzheimers disease and schizophrenia. 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, we developed a new simplified version of sPAL, termed 2-object sPAL by applying a reduced number of objects and trial types for sPAL. In this task, mice could reach learning saturation fast in 6 days. Our pharmacological experiments indicate that the function of the dorsal hippocampal CA1 region is necessary for the performance of the two PAL tasks with the new conditions and the new 2-object sPAL. This work has considerably improved the usefulness of the touchscreen PAL tasks to increase the learning rate, but they remain highly hippocampus-dependent object-location memory tasks.