Updating the Cognitive Map: How Brain Regions Synchronise for Navigation

Mapping the Abstract Mind

The human brain navigates abstract concepts using a mechanism remarkably similar to how it traverses physical rooms. A new study asserts that the entorhinal cortex (EC) and the hippocampus (HPC) coordinate this process through a hierarchical, phase-locked signal. Historically, neuroscientists struggled to define exactly how these two regions communicated. While the existence of a cognitive map has been accepted for decades, the specific translation protocol—the language used between the global metrics of the EC and the local data of the HPC—remained an opaque area of study.

The researchers addressed this by designing an object-matching task. Participants unknowingly manipulated object variants arranged in a ring structure around a central prototype. This design allowed the team to isolate navigation directions in a conceptual space rather than a physical one. Functional MRI data measured during the task revealed a distinct threefold spatial periodicity in the hippocampus. This activity tracked the directional vectors from the variants to the centre, providing a clear signal where previous methods might have seen only noise.

Signal Periodicity: Sixfold vs Threefold

The technical core of this analysis rests on the contrast between established grid codes and this newly observed vector sum. The entorhinal cortex is well-documented to operate with a sixfold periodicity—a hexagonal grid system that maps space. In contrast, the study identified a threefold periodicity within the hippocampus. The authors propose an EC-HPC PhaseSync model to explain this discrepancy. In this model, the sixfold activity of the EC projects vectorial representations into the hippocampus. The collection of these vectors does not mirror the sixfold input exactly but aggregates into a threefold pattern. This suggests a precise mathematical reduction occurs, converting raw grid data into specific conceptual directions.

Behavioural performance mirrored this neural activity. The participants' efficiency in the object-matching task synchronised with the threefold hippocampal signal, lending weight to the fMRI findings. The EC-HPC PhaseSync model successfully reproduced this phenomenon, strengthening the argument that grid cells structure hippocampal representations through this periodic mechanism. While the findings are robust within the parameters of the simulation, questions remain regarding how this translates to more chaotic, real-world conceptual navigation where variables are not neatly arranged in a ring.