Spatially Periodic Cells Are Neither Formed From Grids Nor Poor Isolation

TL;DR

This study demonstrates that spatially periodic cells in rodents are not simply formed from grid cells or due to poor spike isolation, highlighting the existence of diverse spatial representations beyond classic grid patterns.

Contribution

The paper provides evidence that most spatially periodic cells are not derived from hexagonal grid cells and are not artifacts of poor spike isolation, emphasizing the diversity of spatial coding.

Findings

Most SPCs cannot be formed from hexagonal grids

Standard isolation measures are similar for grid and non-grid SPCs

Spikes from different fields of band-like SPCs do not differ

Abstract

Grid cells recorded in the parahippocampal formation of freely moving rodents provide a strikingly periodic representation of self-location whose underlying mechanism has been the subject of intense interest. Our previous work(1) showed that grid cells represent the most stable subset of a larger continuum of spatially periodic cells (SPCs) which deviate from the hexagonal symmetry observed in grid cells. Recently Navratilova et al(2) suggested that our findings reflected poor isolation of the spikes from multiple grid cells, rather than the existence of actual non-grid SPCs. Here we refute this suggestion by showing that: (i) most SPCs cannot be formed from hexagonal grids; (ii) all standard cluster isolation measures are similar between recorded grid cells and non-grid SPCs, and are comparable to those reported in other laboratories; (iii) the spikes from different fields of band-like SPCs do not differ. Thus the theoretical implications of the presence of cells with spatially periodic firing patterns that diverge from perfect hexagonality need to be taken seriously, rather than explained away on the basis of hopeful but unjustified assumptions.