| Co-Investigator(Kenkyū-buntansha) |
HORI Etsuro Toyama Medical and Parmaceutical, University Faculty of Medicine Professor, 医学部, 助手 (90313600)
UMENO Katsumi Toyama Medical and Parmaceutical, University Faculty of Medicine Professor, 医学部, 助手 (90086596)
TABUCHI Eiichi Toyama Medical and Parmaceutical, University Faculty of Medicine Associate Professor, 医学部, 講師 (70272911)
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| Budget Amount *help |
¥3,900,000 (Direct Cost: ¥3,900,000)
Fiscal Year 2001: ¥1,600,000 (Direct Cost: ¥1,600,000)
Fiscal Year 2000: ¥2,300,000 (Direct Cost: ¥2,300,000)
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| Research Abstract |
1. To investigate the role of the medial temporal lobe including the hippocampal formation (HF) in spatial representaion of the outer world, neuronal activity in the HF, and PH was recorded from the monkeys. In the tasks the monkey freely moved to one of 4 reward areas in an experimental field by. Driving cab which the monkey, rode (real translocation task), or freely moved a pointer to one of 4 reward areas on a monitor (virtual translocation task) by manipulating a joystick. 1) Of 389 neurons recorded from the monkey HF, 166 had place fields where neuronal activity increased in a specific area in the experimental field and/or on the monitor (location-differential neurons). In addition, of 163 neuron pairs recorded simultaneously, significant cross-correlation (CCR) peaks were observed in 98 pairs. Task-selective CCRs were observed in 44% (43/98) of neuron pairs. These results suggest that the HF is crucial in allocentric information processing and more over that the HF can encode dif
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ferent reference frames that are context or task dependent. 2) These 166 location-differential neurons, were, analyzed in terms of 16 places in the experimental field or on the monitor by means of the multidimensional scaling (MDS). In the real translocation tasks, the 16 places spread apart in two-dimensional space and their relative positions in a two-dimensional space were well correlated to real positions in the experimental room. However, correlation between spatial arrangements in the MDS-derived and real spaces was significantly smaller in virtual than real translocation tasks. The present results strongly suggest that the ensemble of the HF neurons represent spatial information, and might provide a neurophysiological basis of the cognitive map.
2. Neuronal activity was recorded from the monkey HF while the monkey performed the virtual-reality (VR) navigation task in the virtual space. Some HF neurons displayed place fields where the activity increased in a specific area of the VR space (place differential neurons). The most place-differential neurons showed different responses in different VR spaces. Other neurons responded before or after the reward delivery only in the specific areas. Furthermore, another type of the HF neurons responded during movements in the specific directions. The present results indicated that the monkey HF encoded not only spatial information but also task relevant information such as reward delivery. These specific features of the monkey HF neurons might underlie neurophysiological bases of the human episodic memory.
3. To elucidate the brain mechanisms to encode sequential events, event-related potentials (ERPs) were recorded during a sound sequence discrimination task using young and middle-aged adult subjects. Behavioral results indicated that the young subjects learned the task faster than did the middle-aged subjects. Positive ERP waves were evoked by Targets and Non-targets in the parieto occipital area around 300-700 msec after stimulus onset. The mean amplitudes during this period in the young subjects were larger in Target than Control conditions, and those in Target condition were larger in the young than middle-aged subjects. Furthermore, the mean amplitudes in the Target condition were significantly correlated with behavioral performance, Equivalent dipoles for the ERPs evoked by Targets were estimated in the medial temporal lobe including the hippocampal formation and parahippocampal gyrus. The results suggest that the ERPs around 300-700 msec latency are involved in sound sequence information processing. Furthermore, decrease in amplitudes of this positivity in the middle-aged subjects suggests that age-related memory decline is associated with deficits in encoding and retrieval of unfamiliar sequence. Less
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