Delayed Alternation Task for the Study of Spatial Working and Long Term Memory in Rats.

Memory systems can hold previously presented information for several seconds, bridging gaps between discontinuous events. It has been previously demonstrated that the hippocampus and the medial entorhinal cortex (mEC) are necessary for memory retention over delay intervals in alternation tasks. Here we describe the delayed alternation task, a spatial working memory (WM) task in which animals need to alternate between left and right sides of a figure-8 maze on a trial-by-trial basis to receive a reward. On each trial of this task, the rat has to remember the last episode and turn in the opposite direction compared to the previous trial. We manipulated the WM load by introducing delays of various lengths (10 s and 60 s) between trials. While other alternation task protocols use short delay intervals between trials, our protocol introduces a longer delay condition that requires animals to use long-term memory resources that are not necessarily supported by sequential neuronal firing patterns (i.e., time cells) as are seen with shorter delay intervals.