Constructing the Cognitive Map: How Neural Symmetries Guide Navigation

The study posits that a precise, rhythmic synchronisation between the entorhinal cortex and the hippocampus enables the brain to orient itself toward specific concepts. Historically, isolating the specific mechanism of this coordination has been a persistent challenge for neuroscientists. While the existence of distinct regions for mapping space is established, the mathematical translation between global coordinates and local targets remained opaque.

Defining the Cognitive Map in Mental Space

To investigate this, the team designed a cryptic object-matching task. Participants manipulated object variants arranged in a ring structure around a central prototype, unaware they were navigating a geometric shape. Functional MRI data measured blood flow changes during this process. The analysis focused on how the brain constructs a cognitive map—a mental representation used for navigation in both physical environments and abstract conceptual spaces. The data indicates that navigation is not merely about location but involves a directional vector relative to a 'prototype' centre.

A critical distinction exists between the neural signals observed in these two regions. The entorhinal cortex is characterised by a sixfold periodicity, firing in a hexagonal grid pattern that provides a global metric for space. In contrast, the hippocampus displayed a threefold spatial periodicity in this study. This is a significant technical deviation. While the sixfold signal acts as a rigid coordinate system, the threefold signal appears to be a derivative vector, specifically tracking the direction from an object variant back to the central prototype. The study suggests the brain does not simply copy the grid; it transforms the sixfold input into a threefold output to compute directionality.

The researchers developed an EC-HPC PhaseSync model to validate these observations. This computational framework reproduced the phenomenon, indicating that the sixfold grid activity projects vectorial representations to the hippocampus. Consequently, the collection of these vectors exhibits the observed threefold periodicity. Behavioural performance mirrored this neural pattern. Participants unknowingly performed better when their mental trajectory aligned with this threefold rhythm.

Scepticism is warranted regarding the universality of this mechanism. The task utilised a specific ring-like structure, which naturally lends itself to periodic symmetries. Whether this threefold mechanism applies to irregular, non-circular conceptual spaces remains an open question. Furthermore, fMRI measures haemodynamic responses, which are proxies for neural activity rather than direct measurements of firing rates. Nevertheless, the findings offer a mechanical explanation for how abstract concepts might be organised spatially within the brain.