Functional differentiation in the monkey brain network for memory encoding and retrieval revealed by functional magnetic resonance imaging
健太郎 宮本 · Institutional Repositories DataBase (IRDB) · 2014
Functional magnetic resonance imaging (fMRI) previously revealed the involvement of various cortical regions including the posterior parietal cortex (PPC) and medial temporal lobe (MTL) in human memory processing: retrieval and encoding.However, the corresponding memory-related networks have not been identified in monkeys.In this thesis, awake monkey fMRI, which captures whole-brain activity using an identical paradigm to human studies, was utilized to identify the networks.To localize the memory retrieval network, cortical activity comparisons were made during the correct recognition of previously seen items and rejection of unseen items.Two major PPC activation sites were uncovered that contribute to the retrieval of differentiallypositioned items on a list of sequentially presented pictures: area PG/PGOp in inferior parietal lobule (IPL), along with the hippocampus, was more active for initial item retrieval, while area PEa/DIP in intraparietal sulcus (IPS) was for the last item.Moreover, connectivity from the hippocampus to the PG/PGOp, but not the PEa/DIP, increased during initial item retrieval.Furthermore, the two parietal areas participated in different memory sub-networks, extracted based on functional connectivity among brain-wide retrieval-related regions.To localize the memory encoding network, memory traces predictive of subsequent memory retrieval performance were identified within the caudal entorhinal cortex (cERC) and perirhinal cortex (PRC), both MTL subregions, as well as the hippocampus.Additionally, neuronal activity in the directly-connected cERC/hippocampus, but not the PRC, was responsible for encoding the initial items.These brain region-dependent distinctions involved in memory encoding and retrieval imply a functional correspondence between macaque and human memory networks.