Acknowledgments This paper was written with support from the following grants MHCRC: Neurobiology and Phenomenology of the Major Psychoses (MH43271); Phenomenology and the Classification of Schizophrenia (5R01MH031593); MR Imaging in the Major Psychoses (5R01 MH040856); Training in the Neurobiology of Schizophrenia and evaluation with DTI (Magnotta K award); and BRAINS Morphology
Inhibitors,research,lifescience,medical and Image Analysis (5R01 NS050568). The author has no conflict of interest to disclose that is relevant to the subject of this manuscript.
The introduction of magnetic resonance imaging (MRI) into neuroscience has instigated a revolution in the magnitude and type of research relating brain function to behavior. Functional MRI (fMRI) has been at the forefront of this effort for several reasons. Before MRI, functional neuroimaging was only feasible with radioisotopic tracers such as oxygen-15 labeled water or fluorine-18 Inhibitors,research,lifescience,medical labeled deoxy glucose, and the temporal resolution was in minutes. Such a time resolution precludes detailed mapping of cognitive operations that take place over much shorter epochs. In
Inhibitors,research,lifescience,medical addition to improved temporal resolution down to about 2 to 16 seconds (duration of the “hemodynamic response”), fMRI has provided several other Selleck 5FU advantages relevant to its use in neuroscience: higher spatial resolution, noninvasiveness, lack of ionizing radiation, direct correlation with anatomical imaging, greater repeatability (without limitations of radiation exposure), feasibility in children, and affordability The relative disadvantages are: loud background noise generated by the gradients, need to adapt stimulus Inhibitors,research,lifescience,medical presentation and recording of performance to the magnet bore setting, Inhibitors,research,lifescience,medical low signal-to-noise ratio, lack of quantitation in physiologic units for the most abundant
methods, and the need to exclude individuals with metal in their bodies or who have claustrophobia. With the increased utilization of the method, many of these disadvantages have been addressed through the use of specialized equipment compatible with the MRI environment. As a result, there has been an explosion of studies of fMRI across the neurosciences, both in healthy people and in patients with brain disorders. Blood oxygenation level-dependent see more (BOLD) fMRI This method is the most widely applied in fMRI studies. The technique relies on magnetic susceptibility effects of deoxyhemoglobin, which cause regional signal changes in imaging sequences that are sensitive to susceptibility (eg, echoplanar or routine gradient echo sequences). When the brain is activated by task demands, a net increase in signal intensity is observed in regions activated by the task. This is attributed to a greater increase in regional oxygenated blood flow that exceeds regional oxygen consumption. A variety of pulse sequences can be applied to obtain BOLD measures.