The hippocampus is a medial temporal lobe structure of critical importance for the encoding and retention of episodic memory in general and spatial memory in particular. A milestone in the detection of these hippocampal functions was the discovery that most of the pyramidal cells in the hippocampus exhibit location-specific activity (see Figure 1) and that the activity of such "place cells" is influenced by the training history of the animal. This chapter reviews place cells' governing mechanisms, their ensemble properties, and their possible contribution to spatial memory.

Historical Landmarks

Our understanding of hippocampal place cells rests on two important discoveries from the early 1970s. First, James B. Ranck reported that hippocampal neurones fall into two functionally different classes based on their firing patterns in freely moving rats. Complex-spike cells fired at low rates (normally < 1 Hz), but often in bursts of two to seven spikes at 150-200 Hz...