QUANTITATIVE FMRI: APPLICATIONS

     Functional Magnetic Resonance Imaging (fMRI) is a powerful tool in the field of neuroimaging. This technique is based on Blood Oxygenation Level Dependent (BOLD) contrast, where local changes in the ratio of deoxyhemoglobin and oxyhemoglobin concentrations in the brain lead to variations in the amplitude of the Magnetic Resonance Imaging (MRI) signal. Brain electrical activity demands a constant and high oxygen consumption even at rest. Performing a specific task requires an additional oxygen demand accompanied by an even greater increase in local cerebral blood flow and volume, an effect known as neurovascular coupling. This hemodynamic response results in a decrease in the ratio of deoxyhemoglobin and oxyhemoglobin concentrations with a consequent increase in the effective transverse relaxation time (T2*) in the affected region, which can be detected by MRI equipment.

Although neurovascular coupling has been extensively studied, the vascular response under conditions of reduced oxygenation is an open problem that can be studied using quantitative MRI techniques.

In epilepsy, patients experience epileptiform and spontaneous electrical discharges, often focal. For the treatment of some patients, it is crucial to know the location of the brain region responsible for these discharges. Due to neurovascular coupling, the fMRI technique, alone or in conjunction with electroencephalography, can aid in the localization process.

BOLD contrast, even in a resting state, provides fluctuations in the MRI signal associated with the electrical activity of different brain regions. Functional connectivity between brain areas can be studied based on correlations between spatially distinct time series resulting from MRI. This connectivity has been associated with aspects of human cognition of interest in neuroscience.

In this lecture, we will address quantitative aspects of the fMRI technique, presenting four applications related to the following questions: 1. How does reduced oxygen availability affect the cerebral hemodynamic response? 2. How can fMRI be used to localize epileptogenic zones? 3- Is it possible to control sustained attention using fMRI data? 4- Is there a relationship between brain functional connectivity parameters and human intelligence?