Doubts raised over fMRI Validity
fMRI or functional magnetic resonance imaging, is one of the newer brain imaging techniques, and has seen a flurry of studies using it to try and decode the brain, in the past year. It is almost the new 'fad' in neural study, because of the way it works.
fMRI works based on detection of the dynamic regulation of blood flow in the brain. Medically, this is termed the haemodynamic response, however it is simply tracking brain activity based on increasing and decreasing demand for oxygen and glucose in the haemoglobin of the blood in the brain.
Functional magnetic resonance imaging thusly does not monitor the electrical signals in the brain at all. It cannot tell what signal the neurons are sending, but what it can do is detect exactly which neurons are active, how active they are, and the duration of the activity.
Therein lies the potential problem. FMRI cannot tell what the neurons are actually doing. Therefore, there is the possibility that the strength of correlation between a given task, and the blood flow to a given area of the brain, is not accurately known. FMRI shows a correlation as neurons fire, but it is almost impossible to tell which neurons out of perhaps tens of millions in a given area, are actually firing.
This discrepancy has been well, glossed over by many researchers in the past year, when reporting their findings, thus artificially inflating the degree of discovery of the inner workings of the brain to some extent. Usually, the work itself is accurate, but the degree of correlation is not as strong and cut and dry as the papers postulate.
Now, psychologist Hal Pashler at the University of California, San Diego, and his colleagues, who examined more than 50 studies that relied on fMRI, many published in high-profile journals, and questioned the authors about their methods.
They found discrepancies of the sort listed above, and Pashler's own paper has survived the peer review process itself now, destined publication in Perspectives on Psychological Science. So, this is not the usual claim of a solo scientist spouting off for publicity's sake.
Pashler is not questioning the validity of all the studies, however, many of them use the same data for final correlation as they did for initial data. Pashler is pushing for multiple fMRI scans, and preferably different methods of brain imaging to be used in more studies, so as to fine-tune results and make them more believable.
A row between Pashler's team and several neurological study groups has ignited over this work, and only time will tell as to which side is correct.