Limbic system structures differentially contribute to exploratory trip organization of the rat

The role of limbic system structures in spatial orientation continues to be debated. The hippocampus (HPC) has been implicated in encoding symbolic representations of environments (i.e., cognitive map), whereas entorhinal cortex (EC) function has been implicated in self-movement cue processing (i.e., dead reckoning). These distinctions largely depend on the electrophysiological characteristics of cells within these regions and behavioral tasks that typically fail to dissociate environmental and self-movement cue processing. Topographic and kinematic characteristics of exploratory trip organization have been shown to differentially depend on environmental and self-movement cue processing. The present study examines the effects of either HPC or EC lesions on exploratory trip organization under varying lighting conditions. HPC lesions selectively impaired all measures of performance under dark conditions, but spared all measures of performance under light conditions. EC lesions impaired kinematic measures related to distance estimation under all conditions and impaired all measures of performance under light conditions. These results provide evidence that the HPC is involved in processing self-movement cues but not environmental cues, and EC is involved in processing distance estimates generated from either self-movement or environmental cues. These observations provide further support for serial processing of self-movement cues through limbic system structures that converge on the HPC.