- •Subicular units code space in a heterogeneous manner.
- •We found place cells, barrier-related and grid-like units. These last had spike waveforms similar to axonal recordings.
- •Place cells did not show firing related to physical boundaries in the baseline recordings.
- •Barrier-related cells fired in relation to boundaries. This group included BVC but not all barrier-related were BVC.
- •Firing remapping detected suggests that units firing might be reset by a path integration mechanism.
The subiculum is a pivotal structure located in the hippocampal formation that receives inputs from grid and place cells and that mediates the output from the hippocampus to cortical and subcortical areas. Previous studies have demonstrated the existence of boundary vector cells (BVC) in the subiculum, as well as exceptional stability during recordings conducted in the dark, suggesting that the subiculum is involved in the coding of allocentric cues and also in path integration. In order to better understand the role of the subiculum in spatial processing and the coding of external cues, we recorded subicular units in freely moving rats while performing two experiments: the “size experiment” in which we modified the arena size, and the “barrier experiment” in which we inserted new barriers in a familiar open field thus dividing the enclosure into four comparable sub-chambers. We hypothesized that if physical boundaries were deterministic of the firing of subicular units a strong spatial replication pattern would be found in most spatially modulated units. In contrast, our results demonstrate heterogeneous space coding by different cell types: place cells, barrier-related units and BVC. We also found units characterized by narrow spike waveforms, most likely belonging to axonal recordings, that showed grid-like patterns. Our data indicate that the subiculum codes space in a flexible manner, and that it is involved in the processing of allocentric information, external cues and path integration, thus broadly supporting spatial navigation.
- spatial navigation; subiculum; place cells; grid cells; barriers; tetrodes