Search

The rodent odor span task (OST) uses an incrementing non-matching to sample procedure in which a series of odors is presented and selection of the session-novel odor is reinforced. An OST is frequently used to test the effects of neurobiological variables on memory capacity as the number of odors to remember increases during the course of the session. In this regard, one important finding has been that NMDA receptor antagonists selectively impair OST performance at doses that spare accuracy on control tasks. However, in many versions of the odor span task the number of stimuli to remember is confounded with the number of distractor odors presented to the rat on each trial. The present study compared the effects of the NMDA antagonist dizocilpine when the number of choices was held constant at two (one novel odor-S+ and one previously presented distractor odor-S-) and when the number of choice stimuli was permitted to increase up to 10 (one S+ and 9 S-). Dizocilpine impaired OST accuracy at doses that had no effect on a reference memory control task in both 2-choice and 10-choice conditions; however, the dose-response function was shifted to the left in the 10-choice tests. The impairments produced by dizocilpine were exacerbated as the memory load increased in both 2- and 10-choice conditions. These findings support the hypothesis that NMDA antagonism reduces the number of stimuli that rats can remember accurately, but the interaction between the effective DZP dose and the number of distractors shows that drug effects on OST performances may involve attentional factors in addition to memory capacity. The findings also demonstrate that variations in number of OST distractors can be used to alter sensitivity of the task., (Copyright © 2019 Elsevier Inc. All rights reserved.)

The odor span task is an incrementing non-matching-to-sample procedure designed to provide an analysis of working memory capacity in rodents. The procedure takes place in an arena apparatus and rats are exposed to a series of odor stimuli in the form of scented lids with the selection of new stimuli reinforced. This procedure makes it possible to study drug effects as a function of the number of stimuli to remember. In the present study, the non-selective positive allosteric GABA A receptor modulator flunitrazepam impaired odor span performance at doses that did not affect a control odor discrimination. In contrast, the alpha-1 selective positive GABA A receptor modulator zolpidem and the cholinergic receptor antagonist scopolamine only impaired odor span at doses that produced more global impairment, including decreased accuracy in the control discrimination and increased response omissions in the both the odor span and control discrimination procedures. Even though the effects of flunitrazepam were selective to odor span performance, they did not depend on the number of stimuli to remember-the same degree of impairment occurred regardless of the memory load. These findings suggest that flunitrazepam interfered selectively with conditional discrimination performance rather than working memory and tentatively suggest that flunitrazepam's selective effects in the odor span task relative to the control odor discrimination are mediated by one or more non-alpha1 GABA A receptor subtypes., (Copyright © 2017 Elsevier Inc. All rights reserved.)

The effects of acute and sub-chronic MDMA were assessed using a procedure designed to test rodent working memory capacity: the odor span task (OST). Rats were trained to select an odor that they had not previously encountered within the current session, and the number of odors to remember was incremented up to 24 during the course of each session. In order to separate drug effects on the OST from more general performance impairment, a simple olfactory discrimination was also assessed in each session. In Experiment 1, acute doses of MDMA were administered prior to select sessions. MDMA impaired memory span in a dose-dependent fashion, but impairment was seen only at doses (1.8 and 3.0 mg/kg) that also increased response omissions on both the simple discrimination and the OST. In Experiment 2, a sub-chronic regimen of MDMA (10.0 mg/kg, twice daily over four days) was administered after OST training. There was no evidence of reduced memory span following sub-chronic MDMA, but a temporary increase in omission errors on the OST was observed. In addition, rats exposed to sub-chronic MDMA showed delayed learning when the simple discrimination was reversed. Overall, the disruptive effects of both acute and sub-chronic MDMA appeared to be due to non-mnemonic processes, rather than effects on specific memory functions., (Copyright © 2014 Elsevier Inc. All rights reserved.)

While the Odor Span Task (OST) was developed to assess working memory in rodents, it appears that odor ("What") and time since an odor was last reinforced ("When") jointly control responding in the OST. The OST uses an incrementing non-match to sample procedure such that the number of stimuli to remember increases during the session; the rodent is trained to remember stimuli within a session but not between sessions. We used a variation of the OST to add a "Where" dimension to the task to examine whether rodents could learn to respond to scents based on contextual cues as well. In Experiment 1, 6 rats well-trained on the OST procedure were exposed to four target scents in a holding cage before the OST session began [What-Where-When (WWW) condition]. When these target scents appeared in the OST, rats treated them as novel scents despite their being previously encountered that day; WWW responding was comparable to baseline (BL) responding. Controls were implemented to account for relative familiarity: frequency of target presentation and time since the target odor was presented. On both types of control probes, rats typically responded to target scents less than during WWW or BL conditions, took longer to make a response, and visited more comparison stimuli. In Experiment 2, the study was replicated adding reinforcement delivery for responding to pre-session presentation of target stimuli. Subjects were the same 6 rats plus 2 additional rats also well-trained on the OST. Results were similar to those from Experiment 1. These data indicate that the variables controlling performance on the OST task include What stimulus is presented, Where (i.e., in which location) it was presented, and When it was presented. Thus, the OST-probe methodology may provide a useful vehicle for the study of episodic-like memory processes in non-humans.

The olfactory span task (OST) uses an incrementing non-matching to sample procedure such that the number of stimuli to remember increases during the session. The number of consecutive correct responses (span length) and percent correct as a function of the memory load have been viewed as defining rodent working memory capacity limitations in several studies using the OST. However, the procedural parameters of the OST vary across experiments and their effects are not well understood. For example, in several studies, the number of stimuli to remember is confounded with the number of comparison stimuli displayed in the test arena. Experiment 1 addressed whether performance is influenced by the number of comparison choices available on any given trial (2, 5, 10) as well as the number of odor stimuli to remember during a session (12, 24, 36). Performance was most accurate when the number of stimuli to remember was low, as would be expected from a working memory interpretation of OST. However, accuracy was also affected by the number of comparison stimulus choices. High levels of accuracy were seen even with 36 odors, suggesting that the capacity for odor memory in rats was greater than suggested by previous research. Experiment 2 attempted to define this capacity by programming sessions with 36, 48 or 72 stimuli to remember in a group of rats that had previously received extensive OST training. Highly accurate performance (80% correct or better) was sustained throughout the session at even the greatest memory loads, arguing strongly against the notion that the OST models the limited capacity of human working memory. Experiment 3 explored the possibility that stimulus control in the OST is based on relative stimulus familiarity, rather than recognition of stimuli not yet presented during the current session. Number of odor cups visited increased with the number of comparisons in the arena, but rats rarely sampled all of the comparison odors before responding. However, on probe trials which included only stimuli that had been presented during the session, latency to respond and number of comparisons sampled was sharply increased. These data suggest that responding in the OST is determined not just by relative familiarity, but rather by a more specific "what-when" or perhaps "how long ago" form of stimulus control.

NMDA receptor antagonists interfere with learning and memory in some tasks, but not others. Some recent accounts have suggested that tasks placing demands on working memory are those most likely to be affected, and the present study tested this hypothesis. The purpose of the study was to adapt a recently developed procedure designed to test working memory capacity, the olfactory memory span task, for use in behavioral pharmacology and to then determine the effects of the NMDA receptor antagonist, dizocilpine (MK801) on performance in this task. Rats were trained in a non-match-to-sample procedure under conditions in which they had to remember an increasing number of olfactory stimuli as the session progressed. Simple olfactory discrimination trials were interspersed to provide a performance control. Effects of dizocilpine (.03, .10, .17, .3mg/kg) were determined after stable performances were obtained. Rats were able to sustain stable performances on both the span and simple discrimination tasks with average spans of about 10 items. Accuracy declined as the number of stimuli to remember increased, and dizocilpine impaired accuracy in a dose-dependent and memory-load dependent fashion. The finding that the effects of dizocilpine interacted with the number of stimuli to remember is generally consistent with hypotheses linking NMDA receptors and working memory processes., (Copyright © 2010 Elsevier Inc. All rights reserved.)