Effects of Prior Knowledge on Episodic Memory
Recent neuroimaging studies suggest that the effects of prior knowledge on memory may reflect a relative shift from processing in the medial temporal lobes (MTL) towards processing in the medial prefrontal cortex (mPFC). It is assumed that MTL is important for binding of arbitrary associations, while the mPFC is involved in processing of new information in relation to pre-existing knowledge represented in cortical areas. In my talk, I will present two fMRI studies that tested these hypotheses by examining the emergence of knowledge effects on memory in child development (Study 1) and during intensive learning (Study 2). In Study 1, we developed a novel experimental paradigm in which task-relevant knowledge was experimentally induced to circumvent the collinearity between age and availability of knowledge. A hierarchical knowledge was established to the same level in children of age 8-11 and younger adults. Participants had to remember events that were either congruent or incongruent with the learned hierarchy. For successfully remembered schema-congruent events, we observed stronger mPFC activity in the young adults compared to the children, as well as a correlation between children’s age and mPFC activity. These results suggest that the role of the mPFC for guiding schema-congruent memory retrieval is developing across middle childhood. In Study 2, a sample of medical students who prepared for the state examination was scanned three months prior to (T1) and immediately after (T2) the examination. For successful encoding of knowledge-relevant pairs (face with diagnosis), we found a decrease in hippocampal activation and connectivity with mPFC from T1 to T2. Our results suggest a relative decrease in the importance of hippocampus for memory formation with the increase of knowledge induced by intensive learning.