The left and right rodent hippocampi exhibit striking lateralization in some of the very neural substrates considered to be critical for hippocampal cognitive function. Despite this, there is an overwhelming lack of consideration for hemispheric differences in studies of the rodent hippocampus. Asymmetries identified so far suggest that a bilateral model of the hippocampus will be essential for an understanding of this brain region, and perhaps of the brain more widely. Although hypotheses have been proposed to explain how the left and right hippocampi contribute to behavior and cognition, these hypotheses have either been refuted by more recent studies or have been limited in the scope of data they explain. Here, I will first review data on human and rodent hippocampal lateralization. The implications of these data suggest that considering the hippocampus as a bilateral structure with functional lateralization will be critical moving forward in understanding the function and mechanisms of this brain region. In exploring these implications, I will then propose a hypothesis of the hippocampus as a bilateral structure. This discrete‐continuous hypothesis proposes that the left and right hippocampi contribute to spatial memory and navigation in a complementary manner. Specifically, the left hemisphere stores spatial information as discrete, salient locations, and the right hemisphere represents space continuously, contributing to route computation and flexible spatial navigation. Consideration of hippocampal lateralization in designing future studies may provide insight into the function of the hippocampus and resolve debates concerning its function.

Lateralization is an organizing principle of nervous systems across taxa. The human hippocampus is known to be lateralized with respect to memory and spatial navigation. In contrast, the rodent hippocampus has been traditionally thought of as a bilaterally symmetric structure, as early studies did not uncover functional differences between the left and right hemispheres. Moreover, it is a common view that the primate hippocampus lacks strong, interhemispheric projections between the bilateral hippocampi, which are present in the rodent brain. Advances in experimental technology have resulted in discoveries of hemispheric asymmetries in the rodent hippocampus, which have led to more sophisticated hypotheses of bilateral hippocampal function. Here, we review studies on hippocampal lateralization with a particular focus on the rodent brain, and suggest that there are more similarities between the human and rodent hippocampus than previously thought. We propose novel hypotheses to uncover the contributions of the left and right hemisphere to hippocampal processing and cognition.All rights reserved. No reuse allowed without permission.(which was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.