Those trying to make claims about neural correlates of cognition have mainly relied on brain scans. The approach of such claimants has been to use fMRI scans, which do not directly measure neural activity, but instead measure differences in oxygen or blood flow in different regions of the brain. The "neural correlates of cognition" theorists try to claim that when some particular cognitive activity is done, some tiny region of the brain shows more activity, as shown in fMRI scans.
Such claims have always been very dubious, for several reasons:
(1) Typically the reported difference in activity during some cognitive activity as shown in the fMRI scan is some unimpressive tiny difference such as 1 part in 200. There is no reason for thinking that so small a change is any good evidence of any part of the brain working harder when some type of mind activity occurs. We would expect so small a fluctuation to occur merely by chance.
Those making claims about neural correlates of cognition have tended to be guilty of a very bad type of visual deception I call "lying with colors." When the deception occurs, some difference of only about 1 part in 200 will be depicted in bright red, against a white background. That creates the impression that the difference is some big difference much greater than the actual difference. What goes on is illustrated in the diagram below.
(2) Typically there is no reliable statistical basis for any claim of a reported difference in activity during some cognitive activity. To make such a claim with any reliability, you would need to do a study scanning hundreds or thousands of people. But typically a scientific study making such "neural correlates of cognition" claim will involve some way-too-small study group size such as only 15 or 20 subjects.
(3) There has always been another reason for doubting the reliability of studies of this type: the fact that neither brain electrical activity nor brain chemical activity is being directly measured by fMRI machines when brain scans are done. Instead, what is being measured is blood flow or oxygen levels in the brain. Those making "neural correlates of cognition" claims will typically try to persuade us that greater blood flow or oxygen means greater brain activity related to cognition.
Recently a new scientific study cast great doubt on such claims. The study is entitled "BOLD signal changes can oppose oxygen metabolism across the human cortex." A press release announcing the study has the headline "40% of MRI signals do not correspond to actual brain activity, study suggests." We read this:
"For almost three decades, functional magnetic resonance imaging (fMRI) has been one of the main tools in brain research. Yet a new study published in Nature Neuroscience fundamentally challenges the way fMRI data have so far been interpreted with regard to neuronal activity. According to the findings, there is no generally valid coupling between the oxygen content measured by MRI and neuronal activity.
First author Dr. Samira Epp emphasizes, 'This contradicts the long-standing assumption that increased brain activity is always accompanied by an increased blood flow to meet higher oxygen demand. Since tens of thousands of fMRI studies worldwide are based on this assumption, our results could lead to opposite interpretations in many of them.' "
