Defined neuronal cell types in the lateral entorhinal cortex supporting object and space coding

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The memory of our daily experiences, so-called episodic memory, is generated by interactions between the hippocampus and various neocortical regions. It is widely assumed that episodic memory consists of three main components: the visual-spatial information stream (the “where” component), the information stream about objects and events (the “what” component), and the temporal information stream (the “when” component). Conceptually, the “where” component supports spatial representations of episodic memories, while the “what” and “when” components are associated with non-spatial representation. One hypothesis posits that the medial entorhinal cortex (MEC) conveys spatial representations, while the lateral entorhinal cortex (LEC) conveys non-spatial representations. However, this simplified dichotomy must be revised. It was recently found that LEC neurons also demonstrate spatial coding properties if the environment is enriched with objects, and vice versa, there are cells in the MEC that are responsive to odours or changes in visual cues. Furthermore, based on virus-mediated tracing, we identified novel glutamatergic and GABAergic projections from the MEC to the LEC that are strongly suggestive for MEC-LEC cross-talk before integration of the information in the hipopcampus. Unlike the MEC that has been extensively studied over the last decade, much less is known about neuronal networks in the LEC and how their activity is modulated by different inputs. Based on molecular marker expression, axonal projection pattern and odour responsiveness, we have identified two distinct neuronal cell types/ensembles in the LEC. Here we propose to study these ensembles with the aim to better understand their contribution for coding of spatial and non-spatial components of an experience, and ultimately the role of the LEC for episodic memory.