Encoding Patterned Spatial Behavior in the Subiculum.

The subiculum, a key component of the medial temporal lobe (MTL), has traditionally been viewed as a relay station for hippocampal output to cortical regions. However, its intricate afferent and efferent connections with diverse brain areas suggest a more independent role in memory and spatial navigation. This review argues that the subiculum encodes regularities in environmental structures (e.g., boundaries, corners, axes) and behavioral patterns imposed by task demands, integrating hippocampal information into schematic representations for goal-directed actions. In conditions where perceptual constraints are dominantly fostering predictable behaviors, subicular neurons exhibit invariant firing properties tied to environmental features, such as boundary vector and axis tuning. However, during task-guided behaviors, subicular firing is further shaped by task-relevant mnemonic constraints, as seen in theta-phase-specific fields that segment space into pre- and postchoice zones, encoding variables such as context and choice. Anatomical evidence, including convergent CA1 inputs and local recurrent connections within the subiculum, supports this function, with subicular outputs to regions like the medial prefrontal cortex facilitating rule-guided action generation. Ultimately, the subiculum transforms granular hippocampal codes into memory schemas, enabling efficient navigation and behavior in complex environments.