Distinct Working Memory for Near and Far in a T-Maze Delayed Alternation Task: Evidence for Dual-Process Dynamics in Hippocampal-Prefrontal Coordination
We recently reported that rats performed better at a task distance of 2 m than at 0 m in a T-maze delayed alternation paradigm using a movable home cage in the longer-delay condition (Takita & Ichitani, 2026). We simultaneously recorded local field potentials from the bilateral prefrontal cortex, intermediate hippocampus, and ventral hippocampus. Across task epochs, coherence and two cross-frequency measures (phase-locking value and modulation index [MI]) revealed differences between correct and error trials in prefrontal interactions with hippocampal subregions. Among these measures, only MI was affected by task distance during the pre-task delay epoch. MI was highest in 2-m error trials and lowest in correct trials. In 0-m error trials, MI transiently increased during arm entry to levels comparable to those in 2-m error trials before declining toward the levels observed in correct trials during the later post-task delay. These MI dynamics appeared to be consistent with distance-dependent differences in behavioral performance. In addition, normalized Correct-Error Indices calculated for each electrophysiological measure revealed differential contributions of prefrontal coupling with the intermediate and ventral hippocampus across task distances. These findings suggest the existence of distinct near and far working memory states underlying distance-dependent behavioral differences, with distinct yet complementary contributions of the intermediate and ventral hippocampus to prefrontal interactions.