Attractor-like Dynamics in the Subicular Complex.

Distinct computations are performed at multiple brain regions during the encoding of spatial environments. Neural representations in the hippocampal, entorhinal and head direction (HD) networks during spatial navigation have been clearly documented, while the representational properties of the Subicular Complex (SC) are relatively under-explored, even though it has extensive anatomical connections with various brain regions involved in spatial information processing. We simultaneously recorded single units from different sub-regions of the SC in male rats while they ran clockwise on a centrally placed textured circular track (four different textures, each covering a quadrant), surrounded by six distal cues. The neural activity was monitored in standard sessions by maintaining the same configuration between the cues, while in cue manipulation sessions, the distal and local cues were either rotated in opposite directions to create a mismatch between them, or the distal cues were removed. We report a highly coherent neural representation of the environment and a robust coupling between the HD cells and the Spatial cells in the SC, strikingly different from previous reports of coupling between cells from co-recorded sites. Neural representations were (i) originally governed by the distal cues under local-distal cue-conflict conditions, (ii) controlled by the local cues in the absence of distal cues and (iii) governed by the cues that are perceived to be stable. We propose that such attractor-like dynamics in the SC might play a critical role in the orientation of spatial representations, thus providing a "reference map" of the environment for further processing by other networks. SIGNIFICANCE STATEMENT The Subicular Complex (SC) receives major inputs from the entorhinal cortex and the hippocampus, and HD information directly from the HD system. Using cue-conflict experiments, we studied the hierarchical representation of the local and distal cues in the SC to understand its role in the cognitive map, and report a highly coherent neural representation with robust coupling between the HD cells and the spatial cells in different sub-regions of the SC exhibiting attractor-like dynamics unaffected by the cue manipulations, strikingly different from previous reports of coupling between cells from co-recorded sites. This unique feature may allow the SC to function as a single computational unit during the representation of space, which may serve as a reference map of the environment.