Hippocampal Complex Spike Cells do not Change Their Place Fields if the Goal is Moved Within a Cue Controlled Environment.

Abstract

It has been shown that most hippocampal complex-spike cells fire at specific locations in relation to a set of controlled spatial cues and that they continue to fire in the appropriate places when the cues are removed (O'Keefe and Conway, 1978; O'Keefe and Speakman, 1987). However, the goal remained in a constant position relative to the controlled cues throughout these experiments. It is therefore possible that the unit firing was related to the goal location and not to the controlled cues as was suggested. For example, firing in a particular location might signal the rat's intention to make a particular turn towards the goal from that location and not the location itself. There are many reasons for believing that this is an unlikely class of explanations; nevertheless a test of this hypothesis was undertaken in the present experiment. Nineteen place units were recorded from three rats as they performed the task of finding the goal location. After obtaining an accurate picture of the place fields in relation to the controlled cues and the goal, the location of the goal relative to the cues was moved and the animal retrained to the new goal. After the new goal was being consistently chosen, a second picture of the place fields of the same units was obtained. If the fields were related to the environment created by the cues then they would remain the same during the two stages of the experiment. If they were related to the goal, or to the intended movements towards the goal, then they would rotate relative to the cues. As expected, the majority of place fields remained in the same place in relation to the cues during the two stages of the experiment and were not influenced by the goal relocation. In only two cases was there any suggestion that the place fields changed their location after the goal was moved. It was concluded that the activity of place cells is related to an animal's location in an environment and that the results accord with cognitive map theory of hippocampal function (O'Keefe and Nadel, 1978).