Functional neuroimaging is the use of neuroimaging technology to measure an aspect of brain function, often with a view to understanding the relationship between activity in certain brain areas and specific mental functions.
It is primarily used as a research tool in cognitive neuroscience and neuropsychology.
Common methods include positron emission tomography (PET), functional magnetic resonance imaging (fMRI), multichannel electroencephalography (EEG) or magnetoencephalography (MEG), and near infrared spectroscopic imaging (NIRSI).
PET, fMRI and NIRSI can measure localized changes in cerebral blood flow related to neural activity..
(http://www.sciencedaily.com/articles/f/functional_neuroimaging.htm)
