Sunday, June 22, 2008

Brain Imaging Is Not Mind Reading

Last November 11th, The New York Times published an op-ed article with the title "This Is Your Brain on Politics." The authors--neuroscientists and political scientists--reported that they had done brain scans of 20 swing voters responding to images of the leading American presidential candidates. For example, they wrote: "Mitt Romney shows potential. Of all the candidate's speech excerpts, Mr. Romney's sparked the greatest amount of brain activity, especially among the men we observed. His still photos prompted a significant amount of activity in the amygdala, indicating voter anxiety, but when the subjects saw him and heard his video, their anxiety died down. Perhaps voters will become more comfortable with Mr. Romney as they see more of him." They also reported that John McCain and Barack Obama elicited "a notable lack of any powerful reactions, positive or negative." This article provoked a letter to the editor signed by 17 neuroscientists who protested the publication of such a crude brain imaging study that had no scientific basis. They noted that "a one-to-one mapping between a brain region and a mental state is not possible." They also indicated that the amygdala cannot provide a brain marker of anxiety, because the amygdala is activated not just by anxiety but also by various kinds of arousal and positive emotions.

This illustrates what I called last year "the brain imaging fallacy." That post can be found here. The fallacy is the assumption that a brain image--as in functional magnetic resonance imaging (fMRI)--is a photograph of the mind at work. Almost every day, there is a new report from proponents of "neuroeconomics," "neurolaw," or "neuroethics" who claim to have brain scans showing the mental activity associated with economic, legal, or ethical behavior.

There seems to be a growing recognition in the scientific community about the serious ramifications of this brain imaging fallacy. Recently, the two most important journals of science have published articles on this problem. Nature (June 12, 2008) has published an article by Nikos Logothetis on "What we can and what we cannot do with fMRI." Science (June 13, 2008) has published an article by Greg Miller on "Growing Pains for fMRI." The scientific and philosophical difficulties with brain imaging have been surveyed recently in an article by Adina Roskies in the journal Neuroethics. The winter, 2008 issue of The New Atlantis has articles by O. Carter Snead and Matthew Crawford on the implications of "neuro-talk" for law and morality.

Here are some of the difficulties that contribute to the brain imaging fallacy.

1. Functional neuroimaging is not a direct measure of neuronal activity because it measures only indirect surrogates--particularly, the flow of oxygenated blood.

2. The interpretation of these brain scans depends on elaborate theoretical assumptions about the relationships between blood flow and neural activity.

3. Many different kinds of brain activity can produce the same fMRI signal.

4. No two brains are alike in their structure or functioning, and therefore brain scans require an averaging procedure.

5. Interpreting these brain scans assumes that mental activity can be decomposed into distinct parts corresponding to distinct parts of the brain, although the interconnectedness of brain activity make this unlikely to be completely true.

6. Although the sensory and motor activities of the brain do seem to be clearly localized in identifiable parts of the brain, it is much more speculative to assign the higher cognitive activities to particular parts of the brain.

7. Although brain scans and neuroscience generally show clearly that the brain supports mental activity, this does not show how the brain does this.

8. Since the mind is an emergent property of the brain, the mind depends on, but is not simply reducible to the brain; and this gap is most evident in the contrast between our subjective experience of consciousness and the objective study of the brain in neuroscience. There will always be a gap between our scientific observation of brains at work and our introspective knowledge that comes from our first-hand experience.

As I have argued on this blog and in Darwinian Conservatism, the scientific study of the human mind can clarify but not resolve one of the deepest mysteries of human experience--the emergence of the soul in the brain.

Those who interpret brain imaging as supporting a reductionist materialism conclude that this denies the traditional moral and legal standards of individual choice and responsibility. But once we recognize the brain imaging fallacy, and see the mind as an emergent product of the brain, it becomes clear that neuroscience does not contradict our traditional understanding of moral choice and legal responsibility as rooted in the power of the mind for deliberate thought and action.

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