Hippocampal place field activity in rats trained to walk forward and backwards

Abstract

To achieve a better understanding of the hippocampus, a brain structure linked to neurodegenerative diseases such as Alzheimer's, the activity of hippocampal neurons in awake behaving animals was monitored. These cells are known as “place cells” because they show increased firing rates at discrete locations in an environment referred to as the neuron's place field. The composite activity of a population of place cells forms a ‘map’ of an environment. When a rat traverses a track in different directions within the same environment, however, the activity of many place cells is typically uncorrelated; that is, few hippocampal neurons show bi‐directional activity. This could be due to changes in head direction, which is used to align place fields to the environment. This experiment investigated bi‐directionality in the place cells of rats trained to maintain the same head direction when traversing a linear track by walking forwards and then returning to the starting position by walking backwards. Although the rats maintained the same head direction, place field activity was not bi‐directional. The independent place maps observed during the forward and backward running conditions could be due to different cognitive strategies that the rats use during these distinct types of behavior. This research was supported by the Howard Hughes Medical Institute ‘06 Grant (#52005889) and the McKnight Brain Research Foundation.