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要旨:
Grid cells in entorhinal cortex of freely moving rodents were proposed to provide a universal
metric of space. They tile the environment into a six-fold symmetric pattern with a particular
orientation relative to the environment. The six-fold rotational symmetry of grid patterns can
be used to predict a macroscopic signal to functional magnetic resonance imaging (fMRI) in
humans [Doeller et al, 2010, Nature]. During hippocampal remapping, grid pattern orientations
in rats also change. The purpose of the present study is to examine whether orientation
changes (i.e. remapping) can also be found in humans. Participants learned object locations
within a virtual room and retrieved locations from different start locations during two scanning
sessions. They then navigated into an adjacent room and repeated the procedure. We
extracted grid orientations from odd trials, and predicted the BOLD response in even trials as
a function of the deviation between running direction and the estimated grid orientation for
each session. This prediction was significant for the right entorhinal cortex, replicating earlier
findings. In 80 of the cases grid cell orientations significantly differed between sessions both
within a room and between rooms. Switching off the virtual environment between sessions
for about one minute was seemingly sufficient for that. For male, but not for female participants,
grid cell orientation was clustered around the random view of the room experienced
at session start. Data suggests that human grid cell orientations can be rather flexible which
might be due to the virtuality of the experience. Grid cell orientation might at least for male
participants be related to the initial view of an environment.
