The hippocampus is thought to be essential to many forms of memory. Elucidating the neural code underlying processing during behavior and later recall may lead to an understanding of specific points of failure in diseases in which the functioning of the hippocampus is compromised, such as schizophrenia and Alzheimer's. An understanding of the neural code is necessary to understand communication between brain areas, which could lead to an ability to directly interface with the hippocampus. The goal of this project is to explore one hypothesis of how the hippocampus takes advantage of the spatial properties of the firing of place cells in forms of memory that are sequential in nature. Place cells in the hippocampus preferentially fire when an animal is in a particular location in a given environment, so the population collectively represents the spatial location of the animal. In addition, the firing rate of place cells can be modulated by non-spatial (e.g., sensory or task-related) information. Not only is information conveyed in the firing rate of place cells, the precie timing of spikes with respect to the ongoing theta cycle has been hypothesized to provide a substrate for linking ordered events. A key question that arises from these facts is how the same cells organize their firing to provide two separate streams of information through two separate aspects of its firing behavior, spike rate and spike timing. During this project, analysis of in vio recordings of the hippocampus during navigation will help answer this question. The properties of place cell firing are noticeably different depending on whether the animal is actively engaged in a task or whether it has already achieved its goal. In the latter case, place cells correspondin to locations the animal traversed on the way to its goal will often fire in events called "sharp-wave ripples," and this firing is thought to correspond to recall or memory consolidation. Considering this function of sharp-wave ripples, one might expect that place cells would continue to represent non-spatial information during these events. Further analysis of in vivo recordings of the hippocampus during sharp waves will address this possibility. Taken together, this project will expand our knowledge about the neural code used in the hippocampus during both memory formation and later recall.
This project is basic research aimed at investigating the neural code of the hippocampus. This understanding will help to shed light on the workings of memory in health so that we can interact with the brain directly, for example with neural prostheses. It will also help in understanding what can go wrong in diseases that affect memory, such as schizophrenia and Alzheimer's.