A canonical input to the head direction compass carries predominantly eye movement signals

In mice, nucleus prepositus hypoglossi (NPH) neurons show predominantly eye-movement encoding, with most apparent angular head velocity (AHV) tuning explained by eye rather than head motion.

• Why it matters: The canonical model assumes the mammalian head direction system updates using AHV relayed from the brainstem, but this relay role for NPH had not been directly tested against simultaneous eye and head signals.
• What they did: The study recorded NPH activity while measuring eye and head movements in mice, used optotagging for NPH projections to the head direction circuit, and fit empirically constrained population models to reconstruct eye position and gaze direction.
• The result: Head-direction readouts failed when eye and head motion were dissociated, overturning the view of NPH as a dedicated AHV relay and implying the HD circuit receives major eye-movement signals.