| 研究実績の概要 |
In this project we aimed study the role of ripples in memory encoding. Since hippocampal ripples are generated in area CA3, we utilized the CA3-tetanus toxin transgenic mouse line to probe the function of ripples in hippocampal memories. We recorded from both mutant and control animals performing spatial navigation tasks, and recording sleep sessions before and after exploration. To encode space rodent hippocampus uses multiple means to achieve this. Firstly place cells modulate their firing rate by position, encoding current position (rate coding). Secondly single place cells modulate their firing through a place field (phase precession). And lastly across the population theta sequences encoding not only current position but current heading of the animal (theta sequences). When we analyzed our data we found that ripples were altered in their frequency, when CA3 output was silenced. Together with this we noted that rate coding and phase precession were unaltered in the mutant mice, such that animals current position was represented reliably. However theta sequences were not detectable across the CA1 population. Essentially CA3 output seemed to be required for the ordering of CA1 activity across a large population of place cells. Our paper on these findings in now in press at Nature Neuroscience. We are continuing to analyze the data further, to specifically address ripples in more detail.
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