As the local stores of oxygen in tissues adjacent to capillaries are transiently consumed by glycolysis and waste products build up, various chemical signals (CO2, NO, H+) cause a vasomotor reaction in arterial sphincters upstream of the capillary bed, causes dilation of these vessels. activated) by a cognitive task such as finger tapping, the additional neural firing and other increased signaling processes result in a locally increased energy requirement, in turn resulting in up-regulated cerebral metabolic rate of oxygen (CMRO2) in the affected brain region 12. When a region of the brain is up-regulated (i.e. This nucleotide is produced principally by the mitochondria from glycolytic oxygenation of glucose, and its production results in carbon dioxide as a byproduct. 7 In order to understand the particular contrast mechanism predominantly used in fMRI it is necessary to first discuss brain metabolism.Īll the processes of neural signaling in the brain, including formation and propagation of action potentials, binding of vesicles to the pre-synaptic junction, the release of neurotransmitters across the synaptic gap, their reception and regeneration of action potentials in the postsynaptic structures, scavenging of excess neurotransmitters, etc., require energy in the form of adenosine triphosphate (ATP) 55. Thus, it is of interest to review the fMRI contrast mechanisms, the strengths and weaknesses, and evolutionary trends of this important tool.įMRI is of course based on MRI, which in turn uses Nuclear Magnetic Resonance coupled with gradients in magnetic field 38 to create images that can incorporate many different types of contrast such as T1 weighting, T2 weighting, susceptibility, flow, etc. Increasingly, fMRI is being used as a biomarker for disease 33, 36, to monitor therapy 54, or for studying pharmacological efficacy 62. The popularity of fMRI derives from its widespread availability (can be performed on a clinical 1.5T scanner), non-invasive nature (does not require injection of a radioisotope or other pharmacologic agent), relatively low cost, and good spatial resolution. Since its inception in 1990, fMRI has been used in an exceptionally large number of studies in the cognitive neurosciences, clinical psychiatry/psychology, and presurgical planning (between 100,000 and 250,000 entries in PubMed, depending on keywords). These metabolic changes can be consequent to task-induced cognitive state changes or the result of unregulated processes in the resting brain. All rights reserved.Functional Magnetic Resonance Imaging (fMRI) is a class of imaging methods developed in order to demonstrate regional, time-varying changes in brain metabolism 3, 37, 49. Further MRI studies are needed to disclose whether the migraine attack is triggered by intrinsic brain dysfunction or external factors.Ĭopyright © 2022 Wolters Kluwer Health, Inc. At present, the heterogeneity of the asymptomatic phase and fMRI findings make it difficult to find common denominator.įMRI studies have captured functional brain changes associated with migraine phases, leading to an improvement of our understanding of migraine pathophysiology. Asymptomatic migraine patients can also experience functional alternations of pain and visual processing brain areas. The visual cortex remains hyperexcitable during the postdromal phase.
During the headache phase, further disruptions of the pontine, thalamic, sensorimotor and visual networks occur, although the hypothalamic activity and connectivity normalizes. Moreover, the visual cortex becomes hyperexcitable during the aura phase. The migraine attack starts with hypothalamic hyperexcitability and early reorganization of the common ascending pain and central trigeminovascular pathways. This review will highlight the major fMRI findings that characterize the different phases of migraine. Brain function in migraine patients has been widely explored using functional MRI (fMRI). Advances in neuroimaging techniques during the past few decades have contributed to our understanding of migraine pathophysiology. The underlying mechanisms of migraine are complex and heterogenous.
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