In a first-of-its-kind study, researchers investigated the relationship between neuron activity and blood flow deep in the brain, as well as how salt consumption affects the brain, resulting in cognitive decline such as Alzheimer's disease.

The hypothalamus, a deep brain region involved in vital body activities such as drinking, eating, body temperature regulation, and reproduction, was the focus of the Georgia State University research.

The activation of neurons causes a surge in blood flow to the area. Neurovascular coupling, also known as functional hyperemia, occurs when blood arteries in the brain called arterioles dilate.

Previous research on neurovascular coupling was limited to the surface of the brain (such as the cerebral cortex). Scientists focused on how sensory stimuli from the environment alter blood flow in these studies.

Little is known about whether the same principles apply to interoceptive signals, which are created by the body.

Scientists used a newly created approach that combines surgical techniques with cutting-edge neuroimaging to investigate this association in brain regions. They were primarily interested in how the hypothalamus, a deep brain area involved in vital physiological functions such as drinking, eating, body temperature control, and reproduction, worked.

Salt was chosen by scientists because the body must carefully regulate sodium levels. The amount of salt in your blood is detected by specific cells in your body.

"When you ingest salty food, the brain senses it and activates a series of compensatory mechanisms to bring sodium levels back down," Javier Stern, professor of neuroscience at Georgia State and director of the university's Center for Neuroinflammation and Cardiometabolic Diseases, said.

"The body does this in part by activating neurons that trigger the release of vasopressin, an antidiuretic hormone that plays a key role in maintaining the proper concentration of salt."

In contrast to prior research that identified a link between neuron activity and increased blood flow, scientists discovered a drop in blood flow as the neurons in the hypothalamus activated.

This phenomenon was named 'inverse neurovascular coupling,' or a decrease in blood flow that causes hypoxia, by scientists. Other distinctions they discovered were that vascular reactions to stimuli are highly localized in the cortex, and dilation happens quickly. The response in the hypothalamus was diffuse and took place over a long period of time.

The research raises important concerns, such as how hypertension affects the brain. It's worth noting that between 50% and 60% of hypertension is thought to be salt-related.

Scientists are now aiming to investigate whether this inverse neurovascular coupling mechanism contributes to the pathology of salt-dependent hypertension in animal models.