The role of the prefrontal cortex in episodic memory, pet studies in normal subjects

grantor: University of TorontoThis thesis documents the findings of a series of positron emission tomography (PET) experiments undertaken to eluicidate the neural correlates of episodic memory--in particular, to understand the functional contributions of the prefrontal cortex to episodic memory. Healthy young adults were scanned using ($\sp{15}$O) -H$\sb2$O-PET imaging as they carried out encoding and retrieval tasks. The data were analyzed using the cognitive subtraction paradigm and Statistical Parametric Mapping technique of image analysis. The results clearly document a differential involvement of the left and right prefrontal cortex in encoding and retrieval respectively. The thesis further suggests that the left prefrontal activation is invoked by the task requirement of "working with meaning" of the stimulus. The results are supportive of a role for the left prefrontal cortex in facilitating the formation of a retrievable engram, regardless of the subject's intention. The right prefrontal cortex is invoked equally in recall and recognition tasks when these tasks are equated for difficulty. The role of the right prefrontal cortex in retrieval as revealed by PET, is consistent with the concept of "retrieval attempt" and is distinguishable for the concept of "ecphory" which may be a medial temporal or posterior association cortex based process. The results are discussed in concert with neuropsychological findings and it is concluded that the prefrontal cortex facilitates memory encoding and retrieval processes--though it may not be the site where the engram resides. The discrepancy with established neuropsychological findings is discussed and directions for future research are outlined.Ph.D