Are Brain Scan Findings Fishy?
Some neuroscientists have long been critical of fMRI brain scans, complaining that the technique’s colorful images may cause their data to be weighted beyond their merit. Now, two skeptical groups have published data suggesting that the way we interpret brain scans is downright fishy.
First, a team led by Craig Bennett of UC Santa Barbara produced a paper impressively titled, Neural correlates of interspecies perspective taking in the post-mortem Atlantic Salmon: An argument for multiple comparisons correction. In simpler terms, the team performed brain scans on dead salmon and measured “activity.”
Neuroskeptic reports on the study:
They put the salmon in an MRI scanner and “the salmon was shown a series of photographs depicting human individuals in social situations. The salmon was asked to determine what emotion the individual in the photo must have been experiencing.”
I’d say that this research was justified on comedic grounds alone, but they were also making an important scientific point. The (fish-)bone of contention here is multiple comparisons correction. The “multiple comparisons problem” is simply the fact that if you do a lot of different statistical tests, some of them will, just by chance, give interesting results. [From Neuroskeptic – fMRI Gets Slap in the Face with a Dead Fish.]
As if dead salmon weren’t enough, researcher Henrik Alle at the Max-Planck Institute in Frankfurt has used new squid findings to question the way scientists intepret brain scans. Researchers have long assumed that squid, which have very large axons (nerve fibers), were a good model for human brain activity. Squid nerves consume large amounts of energy sending out messages, and the same was thought to be true for humans. Alle performed rat studies which showed that rat axons consume only a third as much energy as squid axons, and it is likely that human nerves are closer to rats in messaging efficiency.
Lest we dismiss this work as entirely insignificant, an NPR story notes that the work does have real-world implications:
One reason has to do with our use of fMRI and PET scans, which show the brain at work. “What you see with an fMRI or PET scan is the amount of energy that a given brain region is consuming to carry out a certain function,” says Magistretti.
To fully understand what those scans mean, you have to know precisely where the energy is going. And scientists were misled by the squid model, which assumes most of the energy for brain communication is consumed by the brain cell sending a message.
The new research suggests the real energy drain occurs somewhere else — probably where the message gets transferred to another cell. And Magistretti says that can be a long way from the place where the message originated. [From NPR – Brain Scientists Misled by Squid.]
Neither of these studies automatically invalidates neuromarketing studies that use brain scan data. To me, they are one more indication of the need to make neuromarketing research close the loop: correlate brain scan findings with actual market performance. With that kind of data, neuromarketing leaves the realm of the theoretical (e.g., suggesting that an ad that activates the brain in a certain way is likely to be more effective) and into a proven and practical discipline.