ELECTROPHYSIOLOGICAL MEASURES OF HUMAN MEMORY FUNCTIONS

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The major long-term objective of this project is to advance our understanding of the neurocognitive foundations of human memory. The central memory functions under study are those responsible for the successful recollection of personally experienced episodes. Deficits in episodic memory are extremely common in neurological and psychiatric disorders and in normal aging. However, a critical step towards finding better ways to treat people with memory difficulties is to understand the neurocognitive structure of memory functions in healthy individuals. The proposed research rests on the premise that episodic recollection can be most effectively studied by using methods to monitor the constituent processes as they occur. In other words, neurophysiological measures that correspond to relevant neural computations must be used in order to ultimately decipher the brain substrates of normal and disordered human memory. The proposed research plan includes 9 experiments designed to investigate a range of episodic memory functions using noninvasive recordings of brain potentials from scalp electrodes in healthy volunteers. These event-related potentials (ERPs) appear to be sensitive to processes responsible for effectively encoding and retrieving stored information, as shown in several prior studies supported by the FIRST award. Many of these studies used memory tests in which subjects were not explicitly queried about their memories. These implicit memory tests show that some memory functions are separate from those that give rise to episodic recollection. Contrasts between implicit memory and recollection can thus be extremely informative with respect to both cognitive and neural mechanisms. Accordingly, electrical recordings from the brain will be used to monitor memory functions responsible for both recollection and implicit memory, providing independent measures of memory processing with a temporal resolution unsurpassed by any currently available method for studying the human brain in action. Two supplemental methods will also be used to support neuroanatomical theorizing: functional magnetic resonance imaging (in 2 of the proposed experiments) and brain electrical source modeling. Results from this set of experiments will elucidate a set of neural measures that index specific memory processes. The 3 specific aims are: (1) to provide evidence supporting the idea that measures of the electrical activity of the brain can be used to monitor several functions that contribute to episodic recollection; (2) to directly contrast ERP correlates of episodic recollection and ERP correlates of implicit memory; and (3) to bring data on measures of brain function in human subjects to bear on current neurobiological models of consolidation and retrieval.