A spiking network model of neural pattern separation in the hippocampus

Can you remember your last birthday? -Then chances are you also remember where you were that day. Recent advances at the Center for the Biology of Memory (CBM) in Trondheim, Norway, have shed new light on why this is: a dedicated brain network continually keeps track of where we are -like a neural coordinate system. This area is a primary input to the brain's episodic-memory processor, the hippocampus, and, alas, often the first to be affected by Alzheimer's disease. A common cause of forgetting is storin g a new memory using neurons that are already used to store something else. Avoiding such confusion is an essential memory function referred to as 'neural pattern separation'. During my doctoral work at the CBM we discovered that memory maps are stored s ystematically from small-scale maps at the top of the hippocampus to large-scale maps at the very bottom. Likewise, we have not one, but many coordinate systems arranged correspondingly from small to large scales. By defining random sets of coordinate sys tems, every new memory can have a unique spatial foundation which the hippocampus furnishes with information about what happened at this location and when, effectively creating an episodic memory that is not confused with similar memories, but inextricabl y linked to the location of the event. As for any natural system, close interaction between theory and experiment is key to gaining profound insight into how the normal brain works -a prerequisite for meeting the challenge of treating diseased brains. Dr awing on the exceptional experience in theoretical modeling of neural systems found in Professor Terrence Sejnowski's Computational Neurobiology Laboratory at the Salk Institute (San Diego, USA) we have a unique opportunity to combine state-of-the-art neu ral modeling techniques with the latest experimental research on the spatial representation circuit from CBM, in an effort to develop a detailed mathematical account for neural pattern separation in the hippocampus.