Some Cautions About Jumping on the Brain-Scan Bandwagon

My interest in neuroscience and neuroimaging is primarily as a teacher and textbook author. Like any teacher, I want students to appreciate the astonishing progress being made by neuroscientists. But I also want students (and teachers) to think as critically about findings from brain-scan studies as about findings from any other domain of psychology.

The public has a tendency to equate technology with science, but PET scans and fMRIs are only tools; some people do great science with them, others do poor science with them. And many findings are less solid or meaningful than they first appear to be. Just as we teach students to be wary of poorly designed or interpreted surveys, experiments, and tests, we need to teach them to be wary of flawed methods and exaggerated conclusions in neuroimaging studies.

Critics like Joseph Dumit (2004) and William Uttal (2001) have pointed out some of the methodological and conceptual problems with neuroimaging studies. Because of the high costs involved, most brain-scan studies have used small samples; some studies reported with great fanfare by the media have had only four or five participants. Many confounds can affect the results, such as time of day, anxiety levels of the participants, and presentation rates of stimuli. Further, decisions about color scales and the criteria for setting boundaries that define high, moderate, and low neural activity can accentuate or minimize the contrasts among different brains or brain areas. Such decisions can affect whether the gorgeous images we see at conferences, in articles and textbooks, and in the popular press will be striking, ho-hum—or even misleading.

Many neuroimaging studies are done to identify areas of brain activation associated with particular psychological processes, but those processes are not always well defined. Most behaviors and mental processes denoted by a single term (memory, attention, pattern recognition, etc. ) actually involve an intricate and complicated series of operations; the more complicated these operations are, the less likely it is that they are associated with a single region of the brain. It’s far more likely that they involve the interaction of multiple circuits that communicate back and forth in highly complex and, as of yet, unknown ways.

There’s also the vexing problem of individual differences in brain anatomy. In his 1981 Nobel Prize acceptance speech, Roger Sperry observed that the individuality inherent in brain networks made the uniqueness of fingerprints or facial features seem simple by comparison. But when scans from a number of individuals are averaged or pooled to produce a single image, as they usually are, such individuality tends to get overlooked. Of course, scientists pool or summarize all kinds of data. But because brain scans are so beguiling, students and nonspecialists may not realize that an image of a composite brain with apparently well-demarcated active brain areas may not represent the precise pattern of activity in any of the individual brains studied.

The most important problems discussed by critics like Dumit and Uttal have to do with interpreting the results. If an area “lights up” while a person is doing a task or solving a problem or memorizing a list of words, it could mean any number of things. That area may be the sole locus of the operation; or it may have been disinhibited by some other area that is of equal or greater importance even though less active; or it may be necessary for a particular mental operation but not sufficient unless other areas are also involved; or it may contain neurons that operate less efficiently than do those in other areas and therefore require more glucose. Sometimes it is hard to know whether the image in a brain scan even tells us anything about the operation in question. If a scan shows that a brain area “lights up” when someone is doodling, that doesn’t mean the area is a doodling center!

Most researchers are well aware of these and other problems, and the best research avoids such pitfalls. But as we teach about the wondrous new work in neuroscience, we need to impress on students – and remind ourselves – that even the best brain research can take us only so far. Even if we could monitor every cell and circuit of the brain, we would still need to understand the circumstances, thoughts, and cultural rules that affect whether we are gripped by hatred, consumed with envy, or transported by joy.

REFERENCES

Dumit, J. (2004). Picturing personhood: Brain scans and biomedical identity. Princeton, NJ: Princeton University Press. Uttal, W. (2001). The new phrenology: The limits of localizing cognitive processes in the brain. Cambridge, MA: MIT Press/Bradford Books.


Observer Vol.19, No.9 September, 2006

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