MEG analysis and reconstruction fMRI Cortical coordination dynamics Mouse over to see animation Unlike EEG and MEG, fMRI is a secondary measure of brain activation.
Oxygenated hemoglobin is diamagnetic while deoxygenated hemoglobin is paramagnetic.
When neurons fire, they consume oxygen causing an initial reduction in local oxygenation levels. This decrease is then followed by an increase above the resting level as nearby capillaries dilate to allow more oxygenated blood into the active area, overcompensating for the initial decrease. As a result, activation of neurons in a particular area of the brain results in an increase of the recorded signal levels. Areas of the brain associated with particular tasks can then be determined by comparing the MR signal intensities measured during task conditions compared to a resting control. The animation shows areas of the brain that were activated during the performance of a finger sequencing task.