The dorsal hippocampus is required for the formation of long-term duration memories in rats

Abstract

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 µg 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.

Intra-dorsal striatal acetylcholine M1 but not dopaminergic D1 or glutamatergic NMDA receptor antagonists inhibit consolidation of duration memory in interval timing

“…To investigate the role of D1 and M1 receptor interactions with NMDA receptors in the DS in the acquisition and consolidation of duration memory, we applied the "time-shift paradigm" [21] with a probe session [22] to the peak interval (PI) procedure. The PI procedure consists of food and empty trials presented in a random order and separated by an inter-trial interval (ITI).…”

“…These previous studies suggest that the time-shift paradigm is suitable for examining the acquisition of duration memory. To study the consolidation of duration memory, we added a "probe session" following the shift session, in which all trials were empty trials and drugs were not administered [22]. Impairment of consolidation is operationally defined as the appearance of impairment in long-term memory with no impairment in short-term memory when the drug is infused before or after the session [6].…”

Intra-dorsal striatal acetylcholine M1 but not dopaminergic D1 or glutamatergic NMDA receptor antagonists inhibit the consolidation of duration memory in interval timing

“…It is The copyright holder for this preprint this version posted May 25, 2021. ; https://doi.org/10.1101/2021.05.24.445416 doi: bioRxiv preprint studies suggest that the time-shift paradigm is suitable for examining the acquisition of duration memory. To study the consolidation of duration memory, we added a "probe session" following the shift session, in which all trials were empty trials and drugs were not administered [22]. Impairment of consolidation is operationally defined as the appearance of impairment in long-term memory with no impairment in short-term memory when the drug is infused before or after the session [6].…”

“…Impairment of consolidation is operationally defined as the appearance of impairment in long-term memory with no impairment in short-term memory when the drug is infused before or after the session [6]. Recently, it has been reported that suppression of dorsal hippocampal activity by muscimol did not affect the acquisition of new duration memory in the shift session but impaired the memory if tested in a probe session the next day without the drug [22]. These findings suggest that short-term memory from recent food trials guided adaptive behavior in the shift session, while long-term memory, which should have been observed in the probe session, did not form.…”

“…Dependent variables 2.1.4.1.Session-by-session analysis Details of the data analysis were performed according to a previous study[22]. Datafrom empty trials were used for the analysis.…”