Learning related modulation of functional retrieval networks in man

The medial temporal lobe has been implicated in studies of episodic memory tasks involving spatio-temporal context and object-location conjunctions. W e have previously demonstrated that an increased level of practice in a fre e-recall task parallels a decrease in the functional activity of several br ain regions, including the medial temporal robe, the prefrontal, the anteri or cingulate, the anterior insular, and the posterior parietal cortices, th at in concert demonstrate a move from elaborate controlled processing towar ds a higher degree of automaticity. Here we report data from two experiment s that extend these initial observations. We used a similar experimental ap proach but probed for effects of retrieval paradigms and stimulus material. In the first experiment we investigated practice related changes during re cognition of object-location conjunctions and in the second during free-rec all of pseudo-words. Learning in a neural network is a dynamic consequence of information processing and network plasticity. The present and previous PET results indicate that practice can induce a learning related functional restructuring of information processing. Different adaptive processes like ly subserve the functional re-organisation observed. These may in part be r elated to different demands For attentional and working memory processing. It appears that the role(s) of the prefrontal cortex and the medial tempora l lobe in memory retrieval are complex, perhaps reflecting several differen t interacting processes or cognitive components. We suggest that an integra tive interactive perspective on the role of the prefrontal and medial tempo ral lobe is necessary for an understanding of the processing significance o f these regions in learning and memory. It appears necessary to develop ela borated and explicit computational models for prefrontal and medial tempora l functions in order to derive detailed empirical predictions, and in combi nation with an efficient use and development of functional neuroimaging app roaches, to further the understanding of the processing significance of the se regions in memory.