Interval timing–the perception of durations mainly in seconds or minutes–is a ubiquitous behavior in organisms. Animal studies have suggested that the hippocampus plays an essential role in duration memory; however, the memory processes involved are unclear. To clarify the role of the dorsal hippocampus in the acquisition of long-term duration memories, we adapted the "time-shift paradigm" to a peak-interval procedure. After a sufficient number of training sessions with an initial target duration (20 s), the rats underwent "shift sessions" with a new target duration (40 s) under a muscimol (0.5 g per side) infusion into the bilateral dorsal hippocampus. The memory of the new target duration was then tested in drug-free "probe sessions," including the empty trials in which any lever presses were not reinforced. In the probe sessions, the mean peak function of the muscimol group was located leftward to the control group, but these two functions were superimposed on the standardized time axis, suggesting a scalar property. In the session-by-session analysis, the mean peak time (an index of timing accuracy) of the muscimol group was lower than that of the control group in the probe sessions, but not in the shift sessions. In the trial-by-trial analysis, the mean start time and stop times (indices of timing accuracy) were lower than in the control group in the probe sessions. These findings suggest that the dorsal hippocampus is required for the formation of long-term duration memories within the range of interval timing.
bioRxiv Subject Collection: Neuroscience