Higher order cognition (e.g., remembering past events, carrying on a conversation, reasoning and problem solving) depends critically on two broad classes of memory function, working memory (WM) and long-term memory (LTM). LTM refers to the cumulative record of our past experiences and WM refers to the information from perception and LTM that is currently active, along with the set of reflective processes that maintain and manipulate this information. WM allows us to keep something in mind after the initiation stimulus disappears, make connections and comparisons between events, have control over what we think about, formulate intentions, and make plans. Thus, WM is the cognitive system that comprises both mnemonic processes (i.e. storage and rehearsal) as well as non-mnemonic processes (i.e. executive control processes). The proposal will use functional MRI in healthy young subjects to precisely characterize, both cognitively and neurally, the component processes of WM with an emphasis on executive control processes. The first specific aim is to test two models of PFC organization that claim that this brain region is organized-by-material (i.e. the type of information held in WM) vs. organized-by-process (i.e. the type of processing performed on information held in WM). Specifically, we hypothesize that the PFC is organized in a dorsal/ventral fashion where the ventral PFC provides initial processing and is specialized for the maintenance of information held in WM, whereas the dorsal PFC is engaged during the """"""""manipulation"""""""" of information held in WM. The second and third specific aims are to further characterize the cognitive processes that engage the dorsal and ventral PFC systems. For the dorsal PFC, we will examine two cognitive processes that are essential for the production of flexible, goal-oriented behavior: response selection and goal selection. For the ventral PFC, we will examine the cognitive processes involved in inhibitory control. Finally, the fourth specific aim is to determine the differential contribution of PFC and posterior brain regions (i.e. visual association areas) to WM function. Taken together, these studies will provide a rich database for assessing the role of PFC, and its interaction with other cortical brain regions, in various aspects of complex, goal-oriented behavior.
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