Place field dynamics and directionality in a spatial memory task

In previous studies place fields have been shown to be governed by one or more polarizing stimuli such that rotation of the stimuli caused concomitant rotation of the fields. Place fields have also been observed to persist after removal of stimulus cues. In the present study we confirm the previous findings and report two new responses. Hippocampal place fields were observed to decrease or cease place specific firing after the removal of the polarizing cues. Others increased or initiated place specific firing after cue removal. Thus in these instances place field location was dependent on the orientation of the polarizing cues but place field magnitude was governed by their presence or absence. A subset of the place fields recorded in the present study were found to display directionality. Place field directionality was found to be governed by the polarizing cues such that cue rotation produced concomitant rotation in the direction of maximal firing. However directionally specific firing was unaffected by cue removal. These results suggest that place field directionality is initially set up by the polarizing cues but is subsequently independent of them.