Heather Zeiger: Here.
One of the limitations of fMRI is its qualitative nature. fMRI is qualitative, not quantitative, so its measurements are based on comparisons to a baseline or to a norm. It does not provide a specific indicator of a particular mental state. This can pose difficulties in comparing one individual to another, and in measuring individuals for whom a baseline measurement cannot be taken.
The most problematic situations for qualitative measurements are when a patient is compared to “normal” subjects for a baseline measurement. This draws on too many assumptions for what “normal” brain function is. For example, a patient with schizophrenia is compared to subjects who do not have schizophrenia. However, this presumes that the control group has no other mental issues that may cause an “abnormal” reading.
Furthermore, there is no real definition of a “normal” brain scan. The best that scientists can do is to take a statistical average.
However, even this can be problematic …
Here’s Part I .