Grid cells on steeply sloping terrain: evidence for planar rather than volumetric encoding

Area of Science:

• Neuroscience
• Spatial Cognition
• Computational Neuroscience

Background:

• The hippocampus and entorhinal cortex are key to spatial navigation.
• Grid cells in the entorhinal cortex exhibit spatially localized firing fields in a hexagonal array.
• Grid cells are hypothesized to support metric computations for distance estimation.

Purpose of the Study:

• To investigate whether grid cell representations form a 3D lattice or conform to environmental surfaces.
• To test the prediction that a tilted surface would disrupt a 3D grid lattice.
• To determine if grid cell activity is volumetric or surface-dependent.

Main Methods:

• Computational modeling of grid cell lattices on tilted surfaces.
• Recording neural activity of grid cells in rodents foraging on a 40°-tilted surface.
• Analyzing firing patterns, field size, number of fields, and hexagonal symmetry.

Main Results:

• Simulations predicted reduced coverage, field number, and symmetry on a tilted surface if grids form a 3D lattice.
• Empirical recordings showed grid cell firing patterns were largely preserved on a tilted surface, with increased coverage and field number.
• Slight degradation in coherence and symmetry was observed on the tilted surface.

Conclusions:

• Findings suggest grid cells do not form a rigid 3D lattice but are influenced by the local surface.
• The neural map of space appears to be multi-planar rather than fully volumetric.
• Grid cell activity adapts to surface geometry, supporting a flexible spatial representation.