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Abstract
SummaryGrid cells in the entorhinal cortex (EC) of rodents [1] and humans [2] fire in a hexagonally distributed spatially periodic manner. In concert with other spatial cells in the medial temporal lobe (MTL) [3, 4, 5, 6], they provide a representation of our location within an environment [7, 8] and are specifically thought to allow the represented location to be updated by self-motion [9]. Grid-like signals have been seen throughout the autobiographical memory system [10], suggesting a much more general role in memory [11, 12]. Grid cells may allow us to move our viewpoint in imagination [13], a useful function for goal-directed navigation and planning [12, 14, 15, 16], and episodic future thinking more generally [17, 18]. We used fMRI to provide evidence for similar grid-like signals in human entorhinal cortex during both virtual navigation and imagined navigation of the same paths. We show that this signal is present in periods of active navigation and imagination, with a similar orientation in both and with the specifically 6-fold rotational symmetry characteristic of grid cell firing. We therefore provide the first evidence suggesting that grid cells are utilized during movement of viewpoint within imagery, potentially underpinning our more general ability to mentally traverse possible routes in the service of planning and episodic future thinking.
Highlights
IntroductionAfter learning six object locations, participants were required to both move to and imagine moving to the locations of each object during a period that included both a retrieval and imagination element ( referred to as the imagination block) (Figure 1; see Experimental Procedures)
A virtual reality (VR) object-location memory task was used during fMRI scanning
In concert with other spatial cells in the medial temporal lobe (MTL) [3,4,5,6], they provide a representation of our location within an environment [7, 8] and are thought to allow the represented location to be updated by self-motion [9]
Summary
After learning six object locations, participants were required to both move to and imagine moving to the locations of each object during a period that included both a retrieval and imagination element ( referred to as the imagination block) (Figure 1; see Experimental Procedures). Participants navigated (and imagined navigating) every possible path between the six objects in both directions twice during each block (6 objects, 30 paths, 60 trials per block, 2 blocks per participant). Paths between objects, were chosen to ensure full coverage of heading directions (sampling every 15) in the full 0–360 range. During this period, we defined ‘‘movement,’’ ‘‘stationary,’’ and ‘‘imagination’’ periods and interrogated the data for a grid-like signal during each period
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