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Abstract:
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 (see Figure 1 left side) 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 (see Figure 1 right side). 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.
