Convergent Projections from Perirhinal and Postrhinal Cortices Suggest a Multisensory Nature of Lateral, but Not Medial, Entorhinal Cortex

Thanh P Doan,Maria J Lagartos-Donate,Eirik S Nilssen,Shinya Ohara,Menno P Witter

doi:10.1016/j.celrep.2019.09.005

Thanh P Doan, Maria J Lagartos-Donate + Show 3 more

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https://doi.org/10.1016/j.celrep.2019.09.005

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Abstract

The current model of the organization of the medial temporal lobe (MTL) episodic memory system assumes that two functionally different "where" and "what" pathways enter MTL as parallel parahippocampal cortex (PHC)-medial entorhinal cortex (MEC) and perirhinal cortex (PER)-lateral entorhinal cortex (LEC) streams, respectively. With the use of tract tracing and invitro electrophysiological recordings, we show that, in the rat LEC, all main principal neuron types in layer II receive convergent inputs from PER and postrhinal cortex (POR), homologous to PHC in primates. Projections to MEC from POR are much less prominent than previously assumed. These findings thus challenge the prevailing concept that LEC and MEC are defined by different inputs from the PER and PHC/POR, respectively. Our findings point to LEC as the main parahippocampal multimodal integrative structure whose unique set of external sensory-derived inputs allows its network to represent a continuously fluctuating extrinsic environment.

Highlights

The entorhinal cortex (EC) is the main hub connecting the cortex with the hippocampal formation (HF)
This model is based on several seminal neuroanatomical studies that have been taken to indicate that parahippocampal cortex (PHC) carrying visuospatial information and perirhinal cortex (PER) carrying object information are among the principal and categorical inputs to medial entorhinal cortex (MEC) and lateral entorhinal cortex (LEC), respectively (Suzuki and Amaral, 1994; Naber et al, 1997; Burwell and Amaral, 1998b; Schultz et al, 2012; Maass et al, 2015; Navarro Schroder et al, 2015)
In contrast to that model, we demonstrate anatomically that, in the rat, the entorhinal projections originating in postrhinal cortex (POR) preferentially target LEC instead of MEC

Summary

Graphical Abstract

Doan et al demonstrate with the use of tract tracing and in vitro electrophysiological recordings that the rat lateral entorhinal cortex receives convergent perirhinal and postrhinal inputs. They further argue that a comparable input organization scheme exists in the primate, challenging the prevailing concept of parallel parahippocampal pathways to the hippocampus. 2019, Cell Reports 29, 617–627 October 15, 2019 a 2019 The Authors.

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