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Combined Functional Neuroimaging and Transcranial Magnetic Stimulation Studies of Verbal Short-Term Memory


Abstract
The ability to maintain information in mind over short periods of time, what has been termed "short-term memory", is critical to human cognition. Recent research has revealed at least two forms of verbal short-term memory- one that serves to maintain the phonology (or sound-based representations) of verbal input and another that serves to maintain semantic information (or meaning-based representations).  Studies of brain­ damaged patients suggest that each form of verbal short-term memmy is supported by a unique network in the brain, with semantic short-term memmy supported by the inferior frontal lobe and middle temporal areas and phonological short-term memory supported by the inferior parietal lobe and superior temporal areas.  Functionalneuroimaging studies (Mmtin eta!.,  2003) have provided support for this distinction, but other studies have provided conflicting data (Barde & Thompson-Schili, 2002).  The proposed collaboration employs advanced neuroimaging methods to better define the brain areas subserving each form of short-term memory and to better understand the connectivity between different brain areas active in each network.  Neuroimaging data will then be used to conduct a transcranial magnetic stimulation (TMS) experiment, which safely disrupts brain function in small areas of cortex. TMS allows one to distinguish between areas that arc causally involved in a given network and those areas that might be spuriously activated for reasons unrelated to the function of interest.  Combined neuroimaging and TMS studies, which provide the strongest available evidence for making causal inferences about brain organization, have yet to be applied to verbal short­ term memory and require collaborators with unique areas of expertise.  The proposed experiments have the potential to better delineate the brain networks involved in short­ term memmy, which would advance our understanding of how these processes are engaged in healthy individuals and how they may be disrupted in disorders such asstroke, ncurodegenerative conditions, and epilepsy.