Using neuroimaging to explore pattern separation and the aging hippocampus
The hippocampus plays a critical role in memory and disruptions of the hippocampus have been observed in numerous diseases (e.g., Alzheimer's disease, schizophrenia, depression, sleep disorders, etc.). Our understanding of the hippocampus has been advanced recently by experimentally testing computational models’ predictions about the role of hippocampal subfields in pattern separation and pattern completion. Pattern separation reduces the overlap between representations of memories so that new memories might be formed without suffering high levels of interference. In contrast, pattern completion fills in degraded representations based on previously stored information. Numerous theories suggest that the dentate gyrus performs a particularly strong pattern separation function and several theories of adult neurogenesis place strong emphasis on the role of neurogenesis in pattern separation. I will describe fMRI studies that support the view that pattern separation is performed by the hippocampal dentate gyrus and that the dentate acts as a “universal” pattern separator. I will also describe fMRI, DTI, and behavioral findings showing how aging and MCI disrupt this circuit and disrupt pattern separation and how these might be used to dissociate age-related changes from early Alzheimer's disease. Finally, I will describe a new project that capitalizes on magnetic resonance spectroscopy (MRS) to explore the excitatory activity that may reflect age-related changes in the hippocampus.
Dr. Craig Stark is a Professor of Neurobiology and Behavior at the University of California-Irvine.