Bat and rat neurons differ in theta-frequency resonance despite similar coding of space.

Both bats and rats exhibit grid cells in medial entorhinal cortex that fire as they visit a regular array of spatial locations. In rats, grid-cell firing field properties correlate with theta-frequency rhythmicity of spiking and membrane-potential resonance; however, bat grid cells do not exhibit theta rhythmic spiking, generating controversy over the role of theta rhythm. To test whether this discrepancy reflects differences in rhythmicity at a cellular level, we performed whole-cell patch recordings from entorhinal neurons in both species to record theta-frequency resonance. Bat neurons showed no theta-frequency resonance, suggesting grid-cell coding via different mechanisms in bats and rats or lack of theta rhythmic contributions to grid-cell firing in either species.