Contribution of multiple sensory information to place field stability in hippocampal place cells

Hippocampal place cells in rats display spatially selective firing in relat ion to both external and internal cues. In the present study, we assessed t he effects of removing visual and/or olfactory cues on place field stabilit y. Place cell activity was recorded as rats searched for randomly scattered food in a cylinder. During an initial recording session, the lights were o n and the only available cue was a single white cue card. Following this se ssion, three sessions were run in a row with the cue card removed. In addit ion, the lights were either turned off or left on and the floor was either cleaned or left unchanged, thus creating four conditions: dark/cleaning, da rk/no cleaning, light/cleaning, and light/no cleaning. A fifth session was run with the cue card back on the cylinder wall and the lights turned on. T he rat remained in the cylinder during all sessions without being removed a t any time. In the dark/cleaning and light/ cleaning conditions, most place fields were not stable (i.e., abruptly shifted position). In addition, hal f of the cells stopped firing in the dark/cleaning condition. In contrast, in the dark/no cleaning and light/no cleaning conditions, most place fields remained stable across sessions. These results suggest that 1) rats are no t able to rely on only movement-related information to maintain a stable pl ace representation, 2) visual input is necessary for the firing of a large number of cells, and 3) olfactory information can be used to compensate for the lack of visuospatial information. Hippocampus 2000;10:64-76. (C) 2000 Wiley-Liss, Inc.