Place recognition monitored by location-driven operant responding during passive transport of the rat over a circular trajectory

Spatial memory of animals is usually tested in navigation tasks that do not allow recognition and recall processes to he separated from the mechanisms of goal-directed locomotion. In the present study, place recognition was e xamined in rats (n = 7) confined in an operant chamber mounted on the perip hery of a slowly rotating disk (diameter 1 m, angular velocity 9 degrees/s) , The animals were passively transported over a circular trajectory and wer e rewarded for bar pressing when they passed across a 60 degrees-wide segme nt of the path. This segment was recognizable with reference to room landma rks visible from the operant box. Responding defined in the coordinate syst em of the room increased when the chamber entered the 60 degrees-wide appro ach zone, culminated at the entrance into the reward sector, was decreased inside it by eating the available reward, and rapidly declined to zero at t he exit from this zone. When reward was discontinued, the skewed response d istribution changed into a symmetric one with a maximum in the center of th e reward sector. With advancing extinction, the response peak in the reward sector decreased in most rats proportionally to the overall decline of bar pressing. The rewarded and nonrewarded response patterns indicate that pas sively transported rats can recognize their position in the environment wit h an accuracy comparable to that of actively navigating animals and that lo cation-driven operant responding can serve as a useful tool in the analysis of the underlying neural mechanisms.