The Effects of Trial Number and Individual Differences in Exploration on Fish Performance in an Object Location Recognition Task

Frequent exposure to stimuli and testing procedures during repeat experimental trials can enhance the ability of animals to detect and respond to acute environmental change. This is especially relevant for assays which incorporate manipulation of novel objects or test object location recognition. In the spontaneous location recognition (SLR) test, animals are typically given one sample trial where they first encounter identical objects, and then a choice phase where discrimination ability is measured via differences in preferences for an object in a novel location versus one in a familiar location. This preference is based on the animal's propensity to explore and be attracted to novelty. The SLR and similar tests, afford rapid assays of cognition; however, a fundamental question remains outstanding for many species: is there an optimal number of sample trials to ensure learning and discrimination of object locations in the choice phase while also capturing meaningful individual variation within groups? This study investigated the behavioral response of common minnows (Phoxinus phoxinus) to repeated exposures of the SLR's sample phase, and the influence of individual behavioral type (measured as time spent in the center of the open field test) on cognitive performance. Increasing exposure to sample trials increased object exploration and movement in the spatial task. The group exposed to the most sample trials was the only group that learned the task showing significant discrimination between familiar and unfamiliar object locations. Interestingly, there was a preference for the object in the familiar location. Within-group variation in discrimination ability was explained by individual differences in exploration in an open field test. Our results highlight the importance of considering multiple sample trials during SLR testing for this fish species, and more generally how increasing the number of trials and the role individual variation play in cognitive performance.