The role of trial tracking in rats’ working memory

Abstract

The experiments reported in the present study tested whether decreasing intertrial intervals (lTls) intensifies the disruptive effects of increasing retention intervals (RIs) in a delayed conditional discrimination by decreasing the animal's trial tracking accuracy (Cohen & Armstrong, 1996;Cohen & Roberts, 1996). Rats responded on a fixed ratio (FR) 1 or fixed interval (FI) lO-secreinforcement schedule at a second light or tone stimulus, 82, when the first light or tone stimulus, 81, had signaled an FI lO-secor FR 1 schedule, respectively. RIs between 81 and 82 were increased from 3 to 24 sec and never exceeded ITls that were reduced from 24 to 6 sec. For some rats, the trials were separated from each other by extending the lever at 81 and retracting it at the end of 82 (lTI lever-retracted group). For other, control rats, the lever remained extended throughout the session (lever-extended group, Experiment 1) or was extended and retracted with the onset and offset of each stimulus (RI/ITI leverretracted group, Experiment 2). The rats under all trial conditions learned to delay leverpressing on the FI lO-sec schedule. Latency to begin leverpressing on the FI lO-sec schedule declined as RIs were increased, but this effect was attenuated in the ITI lever-retracted groups in both experiments, as would be predicted by the trial tracking hypothesis. Decreasing ITls from 24 to 6 sec intensified the disruptive effects of increasing RIs from 3 to 6 sec in the RIJITI lever-retracted group (Experiment 2), as would be predicted by the trial tracking hypothesis.

Spatial memory in rats after 25 hours

“…Although other studies have documented support for interval-type confusion (e.g., Cohen & Njegovan, 1999; Santi, Keough, Gagne, & Van Rooyen, 2007), we note that earlier studies used a different scale of intervals (in the range of seconds to minutes) compared to the range of hours to days in the present study.…”

“…A number of interesting possibilities were reviewed by Cohen and Njegovan (1999). One possibility is that the buildup of proactive intereference between trials dissipates over longer intertrial intervals (Roberts & Dale, 1981).…”

Spatial memory in rats after 25 hours

“…Our data suggest that the limit of rats' spatial working memory has not yet been reached by 25 hr and that confusion between retention interval and intertrial interval does not account for the observed trial spacing effect. Although other studies have documented support for intervaltype confusion (e.g., Cohen & Njegovan, 1999;Santi, Keough, Gagne, & Van Rooyen, 2007), we note that earlier studies used a different scale of intervals (in the range of seconds to minutes) compared to the range of hours to days in the present study.…”

“…The question remains: why did longer intertrial intervals improve performance? A number of interesting possibilities were reviewed by Cohen and Njegovan (1999). One possibility is that the buildup of proactive intereference between trials dissipates over longer intertrial intervals (Roberts & Dale, 1981).…”

Delayed matching-to-position performance in C57BL/6N mice

“…One may consider that such a species-specific rationale is inconclusive. However, two Another possibility could involve the discriminability of the ITI from the delay interval (Cohen and Njegovan, 1999;Zentall, 1997). In the present study, an ITI was always signaled by turning off the house light as well as by the retraction of all three levers.…”