The heart changes its rhythm, the stomach signals fullness, breathing deepens. Behind these familiar sensations lies a constant exchange of information between the body and the brain. A new study adds an unexpected detail to this picture: blood flow within the brain itself may serve as an additional channel for chemical messages.
Caitlin Carson, Ranjan Roy and Javier Stern of Georgia State University studied two adjacent regions of the brainstem in rats. The results were published on 3 November 2026 in the journal Communications Biology.
The first region is the nucleus of the solitary tract. It is the main receiving hub for information from the internal organs: via the vagus, glossopharyngeal and spinal nerves, data from the cardiovascular, respiratory and digestive systems arrive here. The second region is the area postrema, a tiny portion of the medulla oblongata. Unlike most parts of the brain, it lacks a blood-brain barrier, so it is able to respond to substances circulating in the blood. It is this region that participates in triggering nausea and the vomiting reflex. Together, the two structures help the body coordinate the work of its internal systems.
Anatomists have long suspected connections between their capillaries, but there had been no direct observations in a living brain: the link was inferred from studies on isolated tissues. Now, using two-photon microscopy, it became possible to look into a living brain and trace the path of red blood cells. It turned out that through these connections blood moves predominantly in one direction — from the nucleus of the solitary tract to the area postrema. In a preliminary version of the work (a preprint), such flow was recorded in 12 of 15 studied connections, that is, in roughly 80% of cases, in three rats.
Another finding concerns the structure of the vessels. The capillaries of the area postrema are almost twice as wide as those in the nucleus of the solitary tract: about 9 µm versus almost 5 µm. The blood flow velocity in both regions is practically the same. The authors explain it this way: narrow capillaries create greater resistance, while wide ones facilitate the passage of blood from the neighboring area. Even velocity, in their view, indicates that the blood supply of the shared vascular network is actively regulated.
Vessels are usually perceived as a delivery system for oxygen and nutrients. Now it turns out that the very geometry and direction of blood flow can determine which chemical messages reach neighboring areas of the brain. If one region releases signaling molecules into the blood, the directed flow can carry them to another.
For now this is only a hypothesis. The researchers observed the movement of blood but did not measure the transfer of specific signaling substances or test how they act on nerve cells. The experiments were conducted on rats, and the conclusions can be extended to humans only after separate studies.
If the hypothesis is confirmed, the picture of the brain-body connection will become more complex. In addition to the neural pathways through which organs transmit information, a local vascular channel appears between the centers that process it. The work also calls into question the notion of capillaries as passive pipes that merely deliver energy to nerve tissue.
The next question is which messages this flow is capable of carrying and what they change in the functioning of the body.
