A MOVING OBJECT MODULATED HIPPOCAMPAL PLACE CELL ACTIVITY IN RATS

Abstract

We investigated how hippocampal place cells encode a continuously moving object in the environment. Neuronal place cell activities were recorded from freely moving rats when a toy car was introduced in an open field. First, in a freely moving (FM) task without the car, the rats freely navigated inside the open field to acquire intracranial self-stimulation (ICSS) reward by each travel of 150 cm. Second, they were then divided into 2 groups and tested by 2 different tasks. In a car-dependent navigation (CDN) task, a toy car was placed inside the open field. The rat could receive ICSS if it chased and approached the car within 20 cm distance from the car. In a car-independent navigation (CIN) task, the rat could acquire ICSS rewards if it traveled 150 cm path regardless of the car. Place fields remapped more frequently in the CDN than CIN tasks. In both the CDN and CIN tasks, the place neuronal activity was significantly modulated by movement parameters of the rat, car and distance between the car and rat. However, tuning of the place cells to movement variables of the car as well as the rat was more selective in the CDN than CIN tasks, while information regarding movement variables represented by the place cells was larger in the CDN than CIN tasks. These results indicated that place cell activity within the place fields represents not only own location but also movement variables of other moving object in the environment. [J Physiol Sci. 2008;58 Suppl:S142]