Spatial discrimination of visually similar environments by hippocampal place cells in the presence of remote recalibrating landmarks.

Place cells in the rat hippocampus commonly show place-related firing activity in the animal's current environment. Here, we evaluated the capability of the place cell system to discriminate visually identical environments. Place cell activity was first recorded while rats moved freely in a cylinder divided into three connected sectors. Two sectors were visually identical whereas the third sector was made distinctive by the addition of visual and tactile cues. When in a given sector, the rats could not perceive the cues present in the other two sectors. Most cells had distinctive place fields in each sector, including the two identical sectors. To rule out the influence of non-controlled cues, rotations of the cylinder (+/- 120 degrees) were conducted. When successful, cylinder rotations resulted in equivalent field rotation for all cells. These results suggest that the place cell system is able to form a specific spatial representation for all sectors, so that the rat knows, at any time, in which sector it is currently located. Presumably, such discrimination relies on angular path integration in which the computational errors stemming from self-motion cues would be corrected by environmental landmarks provided by the distinctive sector.