The Magic Number 70 (plus or minus 20): Variables Determining Performance in the Rodent Odor Span Task

Area of Science:

• Neuroscience
• Cognitive Psychology
• Animal Behavior

Background:

• The olfactory span task (OST) is used to assess rodent working memory capacity.
• Procedural variations in the OST, such as the number of comparison stimuli, can influence performance.
• Previous studies suggest limitations in rodent working memory capacity based on OST performance.

Purpose of the Study:

• To investigate the impact of procedural parameters on olfactory span task (OST) performance in rats.
• To determine the true working memory capacity of rats using the OST.
• To explore the stimulus control mechanisms underlying responding in the OST.

Main Methods:

• Experiment 1: Varied the number of stimuli to remember (12, 24, 36) and comparison choices (2, 5, 10).
• Experiment 2: Tested rats with extensive OST training on memory loads of 36, 48, or 72 stimuli.
• Experiment 3: Used probe trials with previously presented stimuli to assess stimulus control.

Main Results:

• Performance accuracy decreased with higher memory loads but was also influenced by the number of comparison choices.
• Rats maintained high accuracy (≥80%) even with 72 stimuli, indicating a larger odor memory capacity than previously reported.
• Stimulus control appears to involve more than relative familiarity, potentially incorporating temporal aspects ('what-when' or 'how long ago').

Conclusions:

• Rodent working memory capacity, as measured by the OST, may be greater than previously estimated.
• Procedural details of the OST significantly impact performance and must be carefully considered.
• Odor memory in rats involves sophisticated stimulus control mechanisms beyond simple familiarity.