Which posterior brain regions provide the inputs that let hippocampal and entorhinal map-like codes support navigation?

The entorhinal cortex sends structured spatial signals to the hippocampus

The strongest evidence for a posterior input to hippocampal map-like codes comes from the entorhinal cortex. In a human object-matching task, hippocampal activity showed a threefold periodic pattern that tracked navigation directions, and this pattern was phase-locked with the sixfold periodicity of the entorhinal cortex [3]. A model built to reproduce this effect proposed that grid cells in the entorhinal cortex project vector-like representations to the hippocampus, where the collection of those vectors produces the threefold pattern [3]. That model is an explanation, not a direct measurement of anatomical projections, but it fits the observed coupling between the two regions.

This fits a broader picture in which the entorhinal cortex supplies the global metric framework and the hippocampus supplies local representations, with the two coordinating during navigation [3]. The direction of influence in that coordination is inferred from the phase relationship and the model, not from tracing physical connections in these human participants.

The circuit can run on internally generated signals, not just sensory input

A key question for any input to map-like codes is whether the brain can drive them without external sensory cues. In monkeys performing a mental navigation task, entorhinal cortex neurons showed periodicity and ramping that matched the temporal structure of landmarks the animals could not see [4]. A continuous attractor network model with a Hebbian-like learning rule explained how the system could recall landmarks endogenously, and the model predicted a transient slowing of path integration that was borne out in the firing-rate and behavioral data [4].

This suggests that at least some of the drive to entorhinal spatial codes can come from within the circuit itself rather than from a posterior sensory region. The study recorded only from entorhinal cortex, so it does not identify which upstream regions, posterior or otherwise, might contribute to that endogenous recall.

Posterior entorhinal structure tracks navigational skill

Structural imaging offers a complementary clue. Differences in gray matter volume in the posterior portion of the entorhinal cortex were present in a study relating brain structure to first-person navigational accuracy [5]. That is a correlation between anatomy and behavior, not a demonstration that the posterior entorhinal cortex is the source of the inputs that drive map-like codes. It does, however, place a posterior region of the entorhinal cortex in the same system that supports navigation.

Modulating the circuit changes navigation, but the posterior sources remain open

Noninvasive stimulation of the right hippocampal-entorhinal complex in healthy volunteers improved spatial navigation performance and was correlated with hippocampal activity modulation and decreased grid cell-like activity in the entorhinal cortex [2]. This shows the circuit can be pushed and pulled to change navigation behavior, but the stimulation targeted the complex as a whole rather than any specific posterior input region.

Taken together, the evidence supports the entorhinal cortex as a major source of structured spatial signals to the hippocampus, and it shows that the circuit can generate map-like activity internally [3][4]. What the studies do not do is identify which specific posterior cortical areas provide the inputs that let these codes support navigation. A brain-inspired navigation framework for unmanned aerial vehicles borrows the same place-cell and grid-cell computations for positioning, but it is an engineering analogy rather than a map of the brain's posterior inputs [1].

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