In the spontaneous object-location (SOL) task, the ability to recognize where stimuli were located in a past encounter is assessed. Even if widely used in rodents, several aspects can affect task performance. It is thus important to assess potentially intervening variables in the new monkey SOL task. Here we assessed whether sex (male vs. females), circadian time (morning vs. afternoon) and retention interval (24 vs. 48 h) affect the performance of adult marmosets in this task. Two identical stimuli were initially explored on a 10-min sample trial. Thereafter, preferential exploration of the displaced vs. the stationary object was analyzed on a 10-min test trial. Both sexes similarly explored the displaced object quicker and longer than the stationary item after a 24 h inter-trial interval. This response pattern was also seen when males were similarly assessed in the morning or afternoon. However, males tested after 48 h explored both objects equally and after a similar latency, yet spent more time where the displaced item had been previously located. Task performance was not related to object exploration during encoding and general activity remained constant. Therefore, sex and diurnal variation in circadian time had no effect on this version of the task, whereas place memory naturally decayed after 24 h. Our results underscore the importance of alternative task parameters to evaluate memory decay. Given the widespread use of spontaneous recognition tasks, a more ecologically-inclined task in monkeys will help translate animal data to clinical research.
Keywords: Circadian time; Marmoset; Object location; Recognition; Retention interval; Sex.
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