Brain distributed memory network : Towards the integration of functional imaging study and single-unit neurophysiology.

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1. We successfully launched a functional brain mapping system for macaque monkeys using a 4.7T MRI system (BioSpec47/40; Bruker BioSpin). We can now obtain single-shot EPI images of the entire brain with an in-plane spatial resolution of 1.25mmx1.5mm. We published many important papers (see below) on the functional MRI (fMRI) in monkeys using this system.2. We established a new method which directly compares an activation map obtained from alert behaving monkeys for high-level cognitive tasks with that from humans (Nakahara et al., 2002). It was first applied to the investigation of neural mechanisms underlying correct performance of the Wisconsin Card Sorting Test. It revealed a functional homology between the anterior bank of the arcuate sulcus in monkeys and the dorsal part of the inferior frontal gyrus in humans. This report was highlighted on the inner cover of Science (Vol. 295, No. 5559, 2002). We also identified a functional homology between the cortical eye-movement-related ar … More eas in monkeys (e. g., FEF, LIP) and those in humans (Koyama et al., 2004).3. We developed a novel method that enables us to locate the microelectrode tip in monkey brains at the spatial resolution of 100um using the 4.7T MRI system (Matsui et al., 2007). In this method, the susceptibility-induced effect enhances the detectability of the microelectrode tip, which usually occupies less than a few percent of the volume of an image voxel. It opens a new perspective, in which the localization of microelectrode recording sites in the layers of primate cerebral cortex permits the analysis of relationships between recorded neuronal activities and underlying anatomical connections.4. We revealed the following mechanisms of cognitive memory: (1) forward processing of long-term associative memory in monkey inferotemporal (IT) cortex, particularly, the emergence of associative encoding from area TE to area 36 (Naya et al.,2003), (2) anatomical reorganization of fiber projections from area TE to area 36 related to long-term memory formation (Yoshida et al., 2003), (3) prefrontal neuronal activity related to update of working memory (Ohbayashi et al., 2003; Fukushima et al., 2004), and (4) active maintenance of associative mnemonic signal in IT cortex (Takeda et al., 2005). I also synthesized these observations and proposed a global view of the cognitive memory system (Miyashita, 2004). Less