A vascular code for speed in the spatial navigation system

The vascular dynamics supporting hippocampal spatial navigation during naturalistic behavior remain poorly understood. Here, we used functional ultrasound (fUS) imaging to examine cerebral blood volume (CBV) changes in freely exploring rats. High-resolution imaging during open-field exploration revealed strong correlations between CBV and animal speed across hippocampal-parahippocampal regions. Lagged general linear modeling uncovered hierarchical information flow from the thalamus to the parahippocampal cortex and hippocampal subfields (dentate gyrus, CA1-CA3). This speed-CBV relationship showed sharp spatial specificity to navigation structures. Multivariate decoding demonstrated that CBV signals carry highly accurate encodings of locomotion speed, remaining robust across animals. We also identified slow CBV oscillations aligned with exploratory behavior fluctuations. These findings reveal a hemodynamic signature of speed representation arising from energy demands in continuous attractor networks, where population activity scales quadratically with speed, and establish fUS imaging as a powerful tool for investigating the neurovascular basis of navigation.