Spatio-temporal binding: An adaptation of the peak interval procedure to assess spatio-temporal learning in rats

Time and space are commonly approached as two distinct dimensions, and rarely combined together in a single task. In this project, we designed a new version of the peak interval procedure in which we included a spatial component. The aim of this experiment was to investigate the learning of a spatio-temporal rule in animals. Adult male Sprague-Dawley rats were placed in front of a 5 nose-poke wall where a given hole could be visited after a precise time after a sound onset in a Fixed Interval (FI) schedule. The animals were presented two different contexts, differentiable by the house-light (A-red or B-green), tone frequency (1 or 11 kHz), and spatio-temporal combination rule given by lighting a specific hole and associating it to a specific FI value (i.e., Hole 2-FI 15s vs. Hole 4-FI 60s). Non-reinforced probe trials of longer duration than the FI values (45s for FI15 and 120s for FI60) were pseudo-randomly presented to ascertain temporal peak interval functions. After 8 weeks of training, all the animals were able to differentiate the two contexts as shown by the number of nose-pokes in the correct hole peaking at the appropriate time, while virtually no activity was recorded in the other holes. In a single Pavlovian session of 8 trials, we changed the spatio- temporal rule for half of the animals: in the second context, the hole 1 was reinforced at 30 seconds. Here we showed that this one session was sufficient for the animals to learn the new spatio-temporal association. Contrary to the control group, the experimental group exhibited a behavioral pattern associated to each hole indicative of a possible spatio-temporal binding. Interestingly, the behavior in the other control Context, in which the spatio-temporal rule had not been changed, was preserved in both groups. The experiment was followed for an extra 10 days after the Pavlovian Shift. At the end of the experiment, all the animals were perfectly and fully adapted to new spatio-temporal rule. In conclusion, the study suggests that rats are able to learn a spatio-temporal association in a single session, and that the two (space, time) dimensions may be learned together and not separately.

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