Spatial memory in rats after 25 hours

Abstract

We investigated the time course of spatial-memory decay in rats using an eight-arm radial maze. It is well established that performance remains high with retention intervals as long as 4 hr, but declines to chance with a 24-hr retention interval (e.g., Beatty & Shavalia, 1980b). It is possible that 24 hr reflects a genuine retention limitation of rat spatial memory. Alternatively, it may be possible to identify factors that might support memory performance even after very long delays. The current experiment was conducted to test the above two hypotheses. We evaluated performance using two intertrial intervals (24 and 48 hr) and two retention intervals (1 and 25 hr). Increasing the intertrial interval produced an approximately constant increase in performance for both retention intervals. This improvement is consistent with a trial-spacing effect (i.e., the superiority of spaced over massed trials). Rat spatial memory apparently lasts at least 25 hr.

A test of the reward-contrast hypothesis

“…If reward contrast was responsible for the long-lasting memory in previous source memory experiments, then the matched contrast would be expected to have produced long lasting spatial memory in the current experiment. Contrary to this prediction, spatial memory declined to the level expected by chance after a 24-hour retention interval; spatial memory is typically degraded after approximately a day (Beatty and Shavalia, 1980; Crystal & Babb, 2008). …”

Discrimination of what, when, and where is not based on time of day

“…Therefore, the rats always received the free choice phase at the same time of day. In a separate experiment, we examined forgetting functions of spatial memory and found that rats' accuracy in the radial maze was still high (62%) after 25 h (Crystal & Babb, 2006). The ITI was at least 48 h, in order to reduce similarity of the RI and ITI.…”

Episodic-like memory in animals

“…By contrast, scrub jays have shown what-where-when memory after 5 days [e.g., 9]. It is not known whether rats could remember over such a long retention interval, although techniques to promote long-lasting memories are available [24] and may be expanded. An interesting question for future research is to increase the retention interval and explore the temporal mechanisms that might support memory in these cases.…”