Place cells in rat hippocampus - by Asha Gopinathan
Place cells are hippocampal pyramidal cells that fire when a rat is in a particular location. This location is called the place field of the rat. There are many theories related to the function of these place cells and place fields and whether it helps the rat navigate an environment. Jefferey et al (2007) in a review discuss the multimodal nature of the sensory inputs to these neurons which help them in localizing their position in a particular environment.
The purpose of this simple project undertaken using NENGO was to show the presence of the place cells when a rat is navigating its environment. For this two sets of ' experiments' were done. In the first one, the rat moves from its initial position towards a goal. During this path it encounters the place field of some of its place cells. At this point, to make the demonstration more interesting, it was decided to halve the velocity of the movement of the rat. Thus the rat slows down till it reaches its goal after this point.
In the second experiment, an experiment done by Jefferey and O'Keefe (1999), was repeated. In this a rat was allowed to move in a cage with two cues placed in the walls of the cage.
Each cue- A and B has place fields on the opposite wall to the cue. These cues are then removed and the rat is covered, removed and again put back in the cage. It is seen that the place fields move by 90 degrees to continue facing the cues that they faced before. In contrast to this the place field generated when there is no visual cue, move along with the position of the rat. Here only the first part of this experiment has been replicated in NENGO.
Both experiments are aimed towards giving some idea of the function of place cells and the place fields in a rat's environment. It is also an attempt to use NENGO to code this function.
1)Jefferey, K J: Integration of the sensory inputs to place cells : What, where, why and how ? Hippocampus, 17, 775-785 (2007) 2)Jefferey,KJ, O'Keefe,J : Learned interaction of visual and idiothetic cues in the control of place field orientation. Exp Brain Research, 127, 151-161 ( 1999)