The rodent hippocampus as a bilateral structure: A review of hemispheric lateralization

Abstract

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 No reuse allowed without permission.(which was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.

New boundaries and dissociation of the mouse hippocampus along the dorsal‐ventral axis based on glutamatergic, GABAergic and catecholaminergic receptor densities

“…This would be further in line with the high amount of different cell types in this region (Amaral, 1978;Nó, 1934;Ramón y Cajal, 1911;Scharfman & Myers, 2012) and again matches the multi-receptor profile of human CA4 (Palomero-Gallagher et al, 2020). Besides, recent evidence further supports the idea to think of the hippocampus as a bilateral structure with functional specializations of subfields in either the right or left hemisphere that are accompanied by the asymmetrical presence of neurotransmitter receptor subunit compositions in these subfields and strata (Jordan, 2020;Kawakami et al, 2003;Shinohara et al, 2008;Shipton et al, 2014). Therefore, we cannot exclude that an additional lateralization of the chemoarchitecture of hippocampal subfields per se and in the dorsal-ventral axis exists, which was not in the focus of this study, but should be considered for future studies.…”

Affective dimensions of pain and region -specific involvement of nitric oxide in the development of empathic hyperalgesia

“…Since the strong lateralization of hippocampal functions has been proved (for review see., Jordan 2019) 32 , based on results of our study, left hippocampus maybe exhibit striking functional lateralization in empathic pain, however, electron paramagnetic resonance imaging techniques are needed to clarify the distribution of the NOX in hippocampi.…”

“…As the hippocampus is crucial in learning and memory, and a major player in the emotion-controlling limbic system, and alterations in its functioning have been seen upon the pain experience and in those exhibiting deficits in empathetic responding 30 , it could also play a role in empathetic pain. Strong lateralization of hippocampal function has been demonstrated (for review see Jordan.,) 32 . Based on results of our study, expression of empathetic pain could be lateralized with the left hippocampus exhibiting a more predominant role.…”

Phenylbutyrate ameliorates prefrontal cortex, hippocampus, and nucleus accumbens neural atrophy as well as synaptophysin and GFAP stress in aging mice

“…Learning and memory is a process that involves various structures, nonetheless, the hippocampus and PFC are two of the most involved in these cognitive processes (Eichenbaum, 2017; Floresco, 2015). In addition, it should be noted that the hippocampus is very actively involved in spatial task processes (Eichenbaum et al, 2017; Floresco, 2015; Jordan, 2020). Several reports using the MWM test, a test used to assess spatial learning and memory, have shown that aging reduces both spatial learning and memory (Eichenbaum et al, 2017; Jordan, 2020).…”

“…In addition, it should be noted that the hippocampus is very actively involved in spatial task processes (Eichenbaum et al, 2017; Floresco, 2015; Jordan, 2020). Several reports using the MWM test, a test used to assess spatial learning and memory, have shown that aging reduces both spatial learning and memory (Eichenbaum et al, 2017; Jordan, 2020). In agreement with previous reports in adult mice (Jangra et al., 2017; Xu et al., 2015; Yao et al., 2014), our results suggest that the PBA improves the response of the old mice, in the MWM test, for both the learning and for the memory process.…”