Resting state fMRI as a tool to investigate brain functional connectivity

Functional magnetic resonance imaging (fMRI) is a safe, noninvasive and repeatable MRI technique, used to estimate and localize neuronal activation in the gray matter of the brain, with high spatial (millimeters) and temporal resolution (in the order of seconds). This technique is based on the principle of neurovascular coupling, which implies that an increase in neuronal activity will cause a rise in blood oxygen consumption and a concomitant rise in local cerebral perfusion. This increased blood flow to the activated region alters the ratio between the deoxyhemoglobin and oxyhemoglobin. Deoxyhemoglobin is paramagnetic and, therefore, influences the signal registered in the MRI. This is the so called blood oxygenation level dependent (BOLD). The BOLD response reflects the degree of oxygenation of the blood in capillaries supplying brain tissue, and its neurophysiological basis lies in changes to blood flow and level of oxygenation in response to neuronal activity. That changes in the BOLD signal indirectly reflect neuronal activity.