Structural neurobiology of the entorhinal cortex in healthy and diseased brains.
Menno P. Witter
Kavli Institute for Systems Neuroscience, NTNU Norwegian University of Science and Technology, Trondheim, Norway
The entorhinal cortex is a crucial component of our conscious medial temporal lobe memory system. The quest to understand the system as a key player in learning and memory started in the late 1950th and was boosted by the discovery of spatially modulated neurons in the hippocampus in 1971. Subsequently, many spatially modulated neurons were discovered in the entorhinal cortex and neighboring areas. The current, generally accepted organizational scheme is that the medial entorhinal complex conveys spatial information to HF, the ‘where pathway’, whereas the lateral entorhinal complex conveys information concerning objects, the ‘what pathway’ to HF.
In my presentation I aim to brief you on the development of this scheme and show recent connectional data indicating that this concept needs to be revised. I will elaborate on recent findings indicating that the local networks of the lateral and medial entorhinal cortex are remarkably similar, and emphasize the difference in extrinsic connectivity as a major defining feature for the known functional differences. The lateral entorhinal cortex is a high-order multimodal cortex appropriately positioned to integrate representations of the external world with motivational signals, modulated by planning and decision signals originating from amygdala, orbitofrontal, medial prefrontal and insular cortex.
I will finally touch upon the relevance of basic knowledge on brain connectivity at the level of identified neuron types, in relation to understanding certain brain diseases inflicting our memory system, such as Alzheimer’s disease.