Intracranial self-stimulation facilitates a spatial learning and memory task in the Morris water maze

Learning and memory improvement by post-training intracranial self-stimulation has been observed mostly in implicit tasks, such as active avoidance, which are acquired with multiple trials and originate rigid behavioral responses, in rats. Here we wanted to know whether post-training self-stimulation is also able to facilitate a spatial task which requires a flexible behavioral response in the Morris water maze. Three experiments were run with Wistar rats. In each of them subjects were given at least five acquisition sessions, one daily, consisting of 2-min trials. Starting from a random variable position, rats had to swim in a pool until they located a hidden platform with a cue located on its opposite site. Each daily session was followed by an immediate treatment of intracranial self-stimulation. Control subjects did not receive the self-stimulation treatment but were instead placed in the self-stimulation box for 45 min after each training session. In the three successive experiments, independent groups of rats were given five, three and one trial per session, respectively. Temporal latencies and trajectories to locate the platform were measured for each subject. Three days after the last acquisition session, the animals were placed again in the pool for 60 s but without the platform and the time spent in each quadrant and the swim trajectories were registered for each subject. A strong and consistent improvement of performance was observed in the self-stimulated rats when they were given only one trial per session, i.e. when learning was more difficult. These findings agree with our previous data showing the capacity of post-training self-stimulation to improve memory especially in rats with little training or low conditioning levels, and clearly prove that post-training self-stimulation can also improve spatial learning and memory.