In mice, pain cuts brain blood-flow response by over 50%

Inside the mouse cortex, two sensations that looked much alike to neurons produced sharply different vascular signatures. Ravi Rungta, a professor at Université de Montréal, and Ph.D. student Antoine Malescot found that pain generated a blood-flow response more than 50% lower than touch, even though neural activity was nearly identical in most cortical layers.

That result challenges a simple assumption behind functional magnetic resonance imaging, or fMRI—the technique that infers brain activity from changes in blood oxygenation. For 30 years, fMRI has offered one of the main windows onto the living brain, but it does not directly see neurons firing. The new study shows that similar neural activity does not necessarily produce the same overall blood-flow signal.

The explanation sits in the cortex’s vascular architecture. The researchers identified several independent networks of arterioles, tiny vessels linking arteries and capillaries, that supply different layers and react differently to stimulation. Genetic markers followed neural firing in real time, while far-red imaging reached a full millimeter into the mouse brain, twice the depth previously achievable, allowing the team to observe all six cortical layers.

A potential consequence is more precise interpretation of layer-specific fMRI in research on pain, cognition and neurological disorders. Researchers may need to consider not only how strongly neurons respond, but also which vascular network carries the blood-flow signal. That could matter especially in conditions associated with reduced blood flow in the cortex’s deep layers.

The result remains a mouse study, not a clinical finding. Published in Science, it gives Rungta’s team a direction for testing whether distinct arteriole networks also contribute to chronic pain and neurodegenerative diseases.