Translational differentiation of vertically displaced surfaces by grid cells.

Area of Science:

• Neuroscience
• Cognitive Science
• Spatial Navigation

Background:

• Place and grid cells in rodents and bats primarily support two-dimensional (2D) spatial representations.
• Recent research explores how these neural representations extend to three-dimensional (3D) environments.
• It remains unclear if grid cells integrate vertically separated surfaces into a unified 3D space or maintain distinct planar representations.

Purpose of the Study:

• To investigate whether grid cells represent vertically adjacent horizontal surfaces as a single 3D space or as distinct 2D environments.
• To determine how active locomotion versus passive movement between environments affects grid cell representations.

Main Methods:

• Electrophysiological recordings of grid cells in rats foraging in two vertically separated environments (an open field and an elevated transparent floor).
• Comparison of grid cell activity during active locomotion (via ramp) and passive transport between the two environments.
• Analysis of grid cell firing patterns, including translation and rotation, between the two surfaces.

Main Results:

• Grid cell firing patterns on the elevated surface were translated, but not rotated, relative to the floor environment.
• These translations were consistent across co-recorded grid cells but varied between animals and cell groups.
• Activity remained consistent across active and passive movement conditions.
• Non-grid spatially modulated cells also showed rearranged location preferences between surfaces.

Conclusions:

• The brain treats vertically separated horizontal surfaces as distinct planar environments rather than a unified 3D space.
• Grid cell representations appear to be planar, maintaining a common orientation signal between surfaces.
• Findings suggest spatial navigation mechanisms differentiate between distinct surfaces even when vertically aligned.