Friday, November 21, 2003

12 noon

Redwood Neuroscience Institute

Title: "Remembering Events Past: Neural Mechanisms for Building and Retrieving Memories"

Anthony Wagner

Psychology Department

Stanford University

Abstract:

Episodic memory --- which refers to conscious memory for past experience -- is central to our ability to link the past with the present.  For example, episodic memory supports the ability to recognize a stimulus as having been previously encountered.  In this talk, I will consider the contributions of prefrontal (PFC) and medial temporal lobe (MTL) mechanisms to episodic memory.  Relying on functional magnetic resonance imaging (fMRI) and transcranial magnetic stimulation (TMS) data, and relating these data to animal connectivity, lesion, and electrophysiological data, I will argue that PFC-MTL interactions are critical for effective learning and remembering. 

-- During encoding, fMRI evidence indicates that PFC cognitive control processes provide a top-down signal that modulates inputs to, and perhaps encoding processes in, MTL.  The consequence of TMS to the frontal lobes indicates that these PFC processes play a necessary role in encoding.  Within MTL, fMRI evidence suggests that hippocampal and perirhinal learning mechanisms differentially support the formation of relational and item memories, respectively. 

-- At retrieval, fMRI evidence suggests that PFC control mechanisms maintain and elaborate on retrieval cues in working memory in the course of probing memory.  These pre-retrieval mechanisms are complemented by post-retrieval PFC control mechanisms that monitor the products retrieval.  FMRI evidence suggests that hippocampal mechanisms specifically support the recollection of past details, with the level of recollection impacting demands on PFC monitoring processes. 

Collectively, it will be argued that these data suggest that PFC-MTL interactions during episodic memory take multiple forms, including indirect or direct interactions during event processing and episodic encoding, and during pre- and post-retrieval stages when attempting to recollect the past.