Neurovascular coupling: motive unknown

• Published in: Trends in neurosciences (Regular ed.) Vol. 45; no. 11; pp. 809 - 819
• Main Author: Drew, Patrick J.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.11.2022
• Subjects: Brain - metabolism; cerebral blood flow; cerebrospinal fluid; Hemodynamics; Humans; Hyperemia - metabolism; hypoxia; neuromodulator synthesis; Neurovascular Coupling - physiology; Oxygen - metabolism; red blood cells; red blood cells; neuromodulator synthesis; brain metabolism; hypoxia; cerebral blood flow; cerebrospinal fluid
• ISSN: 0166-2236; 1878-108X
• DOI: 10.1016/j.tins.2022.08.004

In the brain, increases in neural activity drive changes in local blood flow via neurovascular coupling. The common explanation for increased blood flow (known as functional hyperemia) is that it supplies the metabolic needs of active neurons. However, there is a large body of evidence that is inconsistent with this idea. Baseline blood flow is adequate to supply oxygen needs even with elevated neural activity. Neurovascular coupling is irregular, absent, or inverted in many brain regions, behavioral states, and conditions. Increases in respiration can increase brain oxygenation without flow changes. Simulations show that given the architecture of the brain vasculature, areas of low blood flow are inescapable and cannot be removed by functional hyperemia. As discussed in this article, potential alternative functions of neurovascular coupling include supplying oxygen for neuromodulator synthesis, brain temperature regulation, signaling to neurons, stabilizing and optimizing the cerebral vascular structure, accommodating the non-Newtonian nature of blood, and driving the production and circulation of cerebrospinal fluid (CSF). While the brain is metabolically demanding, it is oversupplied with oxygen at baseline, and increases in oxygenation driven by neurovascular coupling do not appear to be required to support neural activity.Many brain regions show absent or inverted neurovascular coupling.Simulations have shown that, given the architecture of the brain vasculature, regions of low blood flow are unavoidable.Rather than supporting the metabolic activity of neurons, neurovascular coupling likely serves other physiological functions. Potential roles for neurovascular coupling include supplying oxygen for neuromodulator synthesis, temperature homeostasis, signaling to neurons, driving cerebrospinal fluid (CSF) circulation, and stabilizing the vascular network.Neurovascular coupling may perform multiple physiological functions other than supplying oxygen for metabolism, and these functions may vary across brain areas and states.