The ability to recognize previously encountered material declines with age and is impaired by neurological dysfunctions such as Alzheimer's disease, stroke, and schizophrenia. The controlled search and decision processes that guide recognition are especially prone to loss in patient populations, and depend on the prefrontal cortex (PFC) and storage mechanisms in the medial temporal lobes (MTL). However, it is unclear how sub-regions of the PFC and MTL contribute to recollection and familiarity based recognition. Moreover, the MTL have mostly been studied with long-term recognition tasks, but recent evidence has uncovered short-term recognition deficits in MTL patients. It is unknown whether their short- term impairments reflect the operations of recollection or familiarity. Critically, if common processes underlie impairments on long and short-term tasks, it would have important medical implications for how we might treat and rehabilitate patients with MTL and PFC damage. The proposed studies aim to identify the roles of MTL and PFC sub-regions to short-term recognition. The contributions of recollection and familiarity processes will be estimated using a novel variation of the Process Dissociation Procedure (PDP). Three complementary experiments, each with a different methodology, will implement the PDP paradigm. First, a functional magnetic resonance imaging (fMRI) study will identify whether the PFC and MTL contributions to short-term recollection and familiarity match those previously identified in long-term recognition tasks. Second, a patient study will elucidate the necessity of the PFC and the MTL for recollection and familiarity. Third, because patient deficits recognition deficits could be secondary to encoding deficits, the necessity of the PFC for recollection and familiarity will be tested in healthy controls undergoing repetitive transcranial magnetic stimulation (r-TMS) to the PFC. These experiments will advance understanding about the regulatory processes and storage structures that mediate memory. Short-term memory and long-term memory are often considered separate entities, and evidence establishing processes or structures common to both would provide valuable insights into memory disorders. Such knowledge could uncover the nature of memory deficits that accompany normal aging, stroke, Alzheimer's disease, schizophrenia, and cardiac arrest. Such knowledge can be used to develop drug and behavioral therapies targeted at improving memory.
