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The intrinsic entorhinal network interfacing hippocampal-cortical interactions

Menno P. Witter

Institute for Experimental and Clinical Neurosciences, Dept. of Anatomy and Neurosciences, VU University Medical Center , Amsterdam , The Netherlands , and Centre for the Biology of Memory, NTNU, Trondheim , Norway

The entorhinal cortex, in particular the superficial layers II and III, have traditionally been pictured as the main source of cortical inputs for the hippocampal formation. The main output from the hippocampal formation back to widespread cortical domains is mediated by way of deep entorhinal layers. Although the precise role of the entorhinal cortex is still poorly understood, it is of interest that it contains the circuitry linking hippocampal output layers (deep) to input layers (superficial). Furthermore, the connectivity between entorhinal cortex and hippocampus can best be described as comprising multiple parallel pathways. In the first part, I will present recent findings using semi-quantitative confocal microscopy and voltage-sensitive dye imaging suggestive for different interactions between entorhinal input and intrinsic hippocampal connectivity in, respectively CA1 and the subiculum. In the second part, the intrinsic organization of the entorhinal cortex will be summarized and integrated with relevant input/output connectivity. On the basis of these findings, I will propose a “working” model of the entorhinal cortex focusing on the complex laminar and modular organization that may underlie unique and complex integrative processing capacities relevant to memory processes.