Within the brain, the regional CBF is spatially as well as temporally coupled to neuronal activity. Increased neuronal activity is accompanied by an increase in CBF, whereas during deactivation CBF is reduced. After more than a century of research, we still do not fully understand the physiological meaning of the regional CBF response to changes in cerebral activity: Vascular coupling may provide a constant glucose and oxygen supply to the activated brain tissue—on the other hand, removal of tissue metabolites as lactate may be the driving force for vasodilation. In addition, it remains unclear which signals initiate the very early blood flow response, and which factors or mechanisms mediate the sustained increase in CBF during increased neuronal activity. The CBF response to functional activation or deactivation of brain tissue induces characteristic changes in hemoglobin oxygenation, leading to microvascular hyper- or hypo-oxygenation, respectively. Stimulation-induced metabolic and vascular responses are utilized to visualize human or animal brain at work and to map brain activity. Neurometa-bolic and neurovascular coupling thus form the physiological basis for modern functional brain imaging techniques such as functional MRI, near infrared spectroscopy, and optical imaging spectroscopy. Therefore we still need to better understand the physiology of neurometabolic and neu-rovascular coupling to fully exploit the potential of modern functional brain imaging.
Capillary recruitment: Opening or closing of capillaries as a mechanism regulating microvascular blood flow according to demand.
Functional brain imaging: Investigation of stimulation-induced active brain areas by utilizing changes of metabolic or vascular parameters.
Initial dip: Early increase of the concentration of deoxyhemoglobin as evidence for early desaturation of hemoglobin and oxidative tissue metabolism at the onset of functional activation.
Neurovascular coupling: Tight temporal and spatial relationship between regional cerebral blood flow and neuronal activity.
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Dr. Lindauer is heading the research group on cerebrovascular regulation within the Department of Experimental Neurology at Charité Hospital in Berlin, Germany. Her research mainly focuses on the investigation of mediators and mechanisms of neurovascular coupling as the basis for functional brain imaging.
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