Blood Flow Waves Wash Across Brain Surface – Neuroscience News

Summary: Researchers visualized the full network of blood vessels in awake mice, discovering rhythmic expansions and contractions that create blood flow waves across the brain’s surface. This study reveals new insights into brain blood supply, though the function of these waves remains unclear.

The findings may impact how fMRI scans are interpreted, adding complexity to our understanding of brain activity. The waves’ potential role in waste removal suggests implications for neurological disorder protection.

Key Facts:

• Blood vessels on the brain’s surface rhythmically expand and contract, creating slow waves of blood flow.
• These waves occur independently of brain activity, suggesting new complexities in interpreting fMRI scans.
• The waves may help mix fluids around brain cells, potentially aiding in waste removal and protection against neurological disorders.

Source: NIH

Researchers have, for the first time, visualized the full network of blood vessels across the cortex of awake mice, finding that blood vessels rhythmically expand and contract leading to “waves” washing across the surface of the brain.

These findings, funded by the National Institutes of Health (NIH), improve the understanding of how the brain receives blood, though the function of the waves remains a mystery.

A network of elastic and actively pumping vessels carrying oxygenated blood span the surface of the brain before entering the cortex. There, they feed into a second network of capillaries that supply oxygen deeper into the tissue.

Using physics-based experimental methods and analyses, the researchers saw that in addition to the pulses of blood flow that occur with each heartbeat, there are slower waves of blood flow changes that sweep across the brain and occur about once every ten seconds.

The change in blood flow that occur with these slow waves was up to 20% of the entire brain blood supply. Surprisingly, this phenomenon was only weakly tied to changes in brain activity.

The waves produced visible bulges in the blood vessels, which will aid in mixing the fluid around the brain’s cells. This has implications in how waste products and other materials are removed from the fluid surrounding brain cells.

Because the waves of bulging blood vessels move in a variety of directions, the authors surmise that the pulses of dilation and contraction of the blood vessels are more likely to be involved in mixing the fluid around them rather than actively moving it in a given direction.

Regardless, this mixing activity could aid in removing misfolded proteins and other components from the brain into the cerebrospinal fluid that surrounds it.

This process is considered an important protective mechanism for a variety of neurological disorders, such as Alzheimer’s disease and other related dementias, and is more active during sleep.  

These findings may also affect current approaches to interpreting fMRI scans, which measure changes in blood oxygenation within brain structures as they are activated. Specifically, the finding that these waves of blood flow changes occur largely independent of brain activity suggests a new level of complexity complication that needs to be considered when interpreting the link between the fMRI data and brain activation. 

Funding: This research was funded in part  by the NIH’s Brain Research Through Advancing Innovative Neurotechnologies^® (BRAIN) Initiative (U19NS123717, R01NS108472), the NIH’s National Institute of Neurological Disorders and Stroke (R35NS097265), the NIH’s National Institute of Mental Health (R01MH111438), and the NIH’s National Institute of Biological Imaging and Bioengineering (U24EB028942, R01EB026936)

About this neuroscience research news

Author: Carl Wonders
Source: NIH
Contact: Carl Wonders – NIH
Image: The image is credited to Neuroscience News

Original Research: Closed access.
“Long-wavelength traveling waves of vasomotion modulate the perfusion of cortex” by Jim Gnadt et al. Neuron

Abstract

Long-wavelength traveling waves of vasomotion modulate the perfusion of cortex

Highlights

• Vaso-oscillations in arteriole diameter modulate the perfusion of blood to cortex
• Modulation during the resting state exceeds that of stimulus-induced activity
• Vaso-oscillations support long-wavelength traveling waves along all arterioles
• Waves along penetrating arterioles are unlikely to translocate interstitial solutes

Summary

Brain arterioles are active, multicellular complexes whose diameters oscillate at ∼ 0.1 Hz. We assess the physiological impact and spatiotemporal dynamics of vaso-oscillations in the awake mouse.

First, vaso-oscillations in penetrating arterioles, which source blood from pial arterioles to the capillary bed, profoundly impact perfusion throughout neocortex. The modulation in flux during resting-state activity exceeds that of stimulus-induced activity.

Second, the change in perfusion through arterioles relative to the change in their diameter is weak. This implies that the capillary bed dominates the hydrodynamic resistance of brain vasculature.

Lastly, the phase of vaso-oscillations evolves slowly along arterioles, with a wavelength that exceeds the span of the cortical mantle and sufficient variability to establish functional cortical areas as parcels of uniform phase.

The phase-gradient supports traveling waves in either direction along both pial and penetrating arterioles.

This implies that waves along penetrating arterioles can mix, but not directionally transport, interstitial fluids.