Functional Magnetic Resonance Imaging - Combining With Other Methods

Combining With Other Methods

It is common to combine fMRI signal acquisition with tracking of participants' responses and reaction times. Physiological measures such heart rate, breathing, skin conductance (rate of sweating), and eye movements are sometimes captured simultaneously with fMRI. The method can also be combined with other brain-imaging techniques such as transcranial stimulation, direct cortical stimulation and, especially, EEG. The fMRI procedure can also be combined with Near infrared spectroscopy (NIRS) to have supplementary information about both oxyhemoglobin and deoxyhemoglobin.

Animals could also serve as subjects, primarily monkeys such as the rhesus macaque. These studies can be used both to check or predict human results and to validate the fMRI technique itself. But the studies are difficult because it is hard to motivate an animal to stay still and typical inducements such as juice trigger head movement while the animal swallows it. It is also expensive to maintain a colony of larger animals such as the macaque.

The fMRI technique can complement or supplement other techniques because of its unique strengths and gaps. It can noninvasively record brain signals without risks of ionising radiation inherent in other scanning methods, such as CT or PET scans. It can also record signal from all regions of the brain, unlike EEG/MEG, which are biased toward the cortical surface. But fMRI temporal resolution is poorer than that of EEG since the HDR takes tens of seconds to climb to its peak. Combining EEG with fMRI is hence potentially powerful because the two have complementary strengths—EEG has high temporal resolution, and fMRI high spatial resolution. But simultaneous acquisition needs to account for the EEG signal from varying blood flow triggered by the fMRI gradient field, and the EEG signal from the static field. For details, see EEG vs fMRI.