Conjoint control of hippocampal place cell firing by two visual stimuli II. A vector-field theory that predicts modifications of the representation of the environment

Changing the angular separation between two visual stimuli attached to the wall of a recording cylinder causes the firing fields of place cells to mov e relative to each other, as though the representation of the floor undergo es a topological distortion. The displacement of the firing field center of each cell is a vector whose length is equal to the linear displacement and whose angle indicates the direction that the field center moves in the env ironment. Based on the observation that neighboring fields move in similar ways, whereas widely separated fields tend to move relative to each other; we develop an empirical vector-field model that accounts for the stated eff ects of changing the card separation. We then go on to show that the same v ector-field equation predicts additional aspects of the experimental result s. In one example, we demonstrate that place cell firing fields undergo dis tortions of shape after the card separation is changed, as though different parts of the same field are affected by the stimulus constellation in the same fashion as fields at different locations. We conclude that the vector field formalism reflects the organization of the place-cell representation of the environment for the current case, and through suitable modification may be very useful for describing motions of firing patterns induced by a w ide variety or stimulus manipulations.