Cosyne 2007 Workshops
February 26-27, 2007
The Canyons, Utah
Hugh Blair
Scale-invariant memory representations emerge from moire interference between hexagonal grid fields encoded by theta oscillations: A computational model
Hugh T. Blair, Adam C. Welday, Kechen Zhang
The dorsomedial entorhinal cortex (dMEC) of the rat brain contains a remarkable population of spatially tuned neurons called grid cells (Hafting et al., 2005). Each grid cell fires selectively at multiple spatial locations which are geometrically arranged to form a hexagonal lattice that tiles the surface of the rat.s environment. Here we show that grid fields can combine with one another to form moiri interference patterns.referred to as .moiri grids..that replicate the hexagonal lattice over an infinite range of spatial scales. We propose that dMEC grids are actually moiri grids formed by interference between much smaller grids, and these smaller grids are referred to as .theta grids. because they are proposed to be encoded by theta oscillations. The formation of moiri grids from theta grids obeys two scaling laws, referred to as the length and rotational scaling rules. The length scaling rule appears to account for firing properties of grid cells in layer II of dMEC, whereas the rotational scaling rule can better explain properties of layer III grid cells. Moiri grids built from theta grids can be combined to form yet larger grids, and can also be used as basis functions to construct memory representations of spatial locations (place cells) or visual images. Memory representations built from moiri grids are automatically endowed with size invariance by the scaling properties of the moiri grids. We therefore propose that moiri interference between grid fields may constitute an important principle of neural computation underlying the construction of scale-invariant memory representations.
