The ability to call to mind past experiences and events is the essence of human memory. Our understanding of this process often called episodic retrieval has been advanced by neuroimaging studies, particularly those involving functional magnetic resonance imaging (fMRI). Brain regions involved in episodic retrieval can be analyzed by measuring activity during successful retrieval of a memory. Two prominent regions have been linked to episodic retrieval the parietal cortex and the prefrontal cortex. Although the role of the prefrontal cortex in memory has been studied extensively, there is less detail about the role of the parietal cortex. With support from the National Science Foundation, Dr. Arthur P. Smimamura of the University of California, Berkeley, will use fMRI to study brain activity during episodic retrieval. Three other tasks will be compared with episodic retrieval of word lists: visuospatial processing (seeing letter strings to the right or left of a target), working memory (remembering the location of visual targets), and semantic retrieval (recalling an experimentally determined piece of information). By having such an array of processes, the role of the parietal cortex in episodic memory should become clear.
Research has recently focused on the dynamics between brain regions, rather than the activity in just one region. Moreover, past investigations have keyed on a particular cognitive process, such as episodic memory or visuospatial attention and their neural correlates, without considering how such processes interact. In the present research program, the contribution of the parietal cortex will be assessed across a variety of tasks, and the degree to which brain responses across these tasks overlap will be investigated. By this analysis, it is hoped that the neural dynamics underlying episodic retrieval will be revealed and clarified. Such insights will help us understand the workings of everyday memory and perhaps to help overcome their loss.
What did you eat for dinner yesterday? Answering this question depends on brain processes that interpret the world around us, store that experience, and enable the retrieval of it at a later time. This kind of memory retrieval, called episodic retrieval, involves the "re-collection" of specific features, such as the place, perceptions, thoughts, feelings, and actions linked to an episode. It is as if we time travel, experiencing the event in our mind by recalling the same features encountered during the event itself. The conundrum of episodic retrieval is that we must self-generate these event events with limited input or cues, such as trying to retrieve an event simply by the cue, "What did you eat for dinner yesterday?" To retrieve successfully such information, we must initiate a search process through memory and recollect the specific ensemble of features that made up the event. In neuroimaging studies, ventral regions of the posterior parietal cortex (vPPC) are particularly active when episodic memories are successfully retrieved. Grant support provided an analysis of the neural correlates of episodic retrieval. A new theory was developed, Cortical Binding of Relational Activity (CoBRA), in which the vPPC acts as a convergence zone that binds episodic features stored in disparate neocortical regions. This process works in conjunction with other known mechanisms, such as those associated with the prefrontal cortex and medial temporal lobe.
