Fourier Series Encoding of Continuous Variables in Entorhinal Cortex

The activity of a grid cell in the medial entorhinal cortex is spatially modulated and peaks when an animal reaches certain locations in its environment. These locations form a regular triangular grid, and every animal has many grid cells that collectively span a wide range of grid spacings. Instead of being smoothly distributed, grid spacings cluster around particular values that form a geometric sequence with ratio in the range 1.3--1.7. I will briefly describe our proposed mechanism for the self-organization for this system through commensurate lattice relationships. Moreover, the grid system is believed to serve as a cognitive map of space. I will review others’ work which shows that a geometric sequence of grid spacings optimizes certain features of spatial representation and allows for a particular type of error correction. Finally, I will describe others’ initial reports that grid cells also exhibit periodic responses to non-spatial sensory and even conceptual dimensions. These findings tentatively suggest that Fourier-like encoding may be a canonical feature of hippocampal-entorhinal circuits and may encourage the audience to ponder new computational motivations for and implications of its existence. The talk (~30min) will be followed by an open discussion.

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