Electrophysiological and spatial characterization of subicular neurons

The subiculum (SUB) is the major output structure of the hippocampus. It is involved in spatial learning and memory and it contains neurons that exhibit different electrophysiological and functional properties. This variety might suggest the involvement of the SUB in multiple circuits supporting distinct cognitive processes. The diversity in projection targets for different cell types further supports this notion. Our study aimed to investigate the electrophysiological properties of neurons in the subiculum, their spatial modulation response, and the relationship between them. We implanted silicon probes in the SUB of mice and we recorded neuronal activity across different spatial contexts. Many of the recorded cells were spatially modulated in at least one of the contexts explored by mice. Among them, we found perimetral-like neurons that fired close to all the borders of the environment. Additionally, we observed cells with the opposite spatial modulation, preferentially firing when the animal was in the center of the arena. Many of these neurons maintained their firing fields after environmental changes were implemented. We also found neurons which firing was similar to boundary vector cells (BVC). Notably, a proportion of these neurons did not behave as BVC when barriers were inserted or when the size of the open field was manipulated. Our preliminary results confirm the importance of the subiculum in the encoding of environmental boundaries, supporting its fundamental role in forming and anchoring spatial maps. However, our results indicate the existence of a higher diversity of spatial neurons in the SUB that previously described.