A dead salmon has become a scientific celebrity after its brain supposedly lit up when shown pictures of humans during a brain scan.
Some bloggers last week reported that the fish was still thinking or that the research is evidence of an ethereal soul. However, the study was done to show that data from an fMRI brain scan can lead to false positives — misleading results — if not carefully analyzed.
Yes, the salmon was dead — bought in a lifeless state at a fish market and scanned an hour later. No, the results are not shocking or miraculous. Like many scientific studies, the study and its results, presented earlier this year in a poster at a conference, are technical and rather bland:
"The goal of the salmon poster was to encourage the minority of researchers who report uncorrected statistics to move forward and begin using basic multiple comparisons correction in their research," says study leader Craig Bennett, a postdoctoral researcher in the Department of Psychology at the University of California, Santa Barbara.
In a nutshell, the data reported by Bennett and colleagues in no way suggests the salmon's brain was functioning, but rather reveal anomalies that can be misleading if you're not careful. [In a separate study recently, researchers concluded that human brain scans are often done unnecessarily.]
The scientific saga of the salmon is as long and complex as a salmon's journey from the ocean to a mountain stream to spawn.
It began in 2005 when Bennett picked up a salmon at a local market. An hour later he and colleagues stuck the fish in an fMRI scanner and did a bunch of different scans as part of a project at Dartmouth College to develop MRI protocols. They had previously scanned a pumpkin and a dead bird.
"The salmon was approximately 18 inches long, weighed 3.8 lbs, and was not alive at the time of scanning," the poster presentation states. "The salmon was shown a series of photographs depicting human individuals in social situations with a specified emotional valence. The salmon was asked to determine what emotion the individual in the photo must have been experiencing."
"By far it was our crowning achievement in terms of ridiculous objects to scan," Bennett recently wrote, on his blog, of the fish.
Another look at the data
Then in 2008, Bennett was working with one of his advisers on a presentation about false positives in MRI data, specifically about misleading results that can come from what's called a "multiple comparisons problem." Bennett ran his 2005 fish data through some statistical programs and, sure enough, three false positives showed up in the salmon's brain.
The results were presented at the Human Brain Mapping conference last June in San Francisco. They almost never saw the light of day, however. In the review process, "Just about everyone thought it was a joke — some rogue student who was playing a prank," Bennett says.
The findings have been submitted to a journal — as a cautionary tale about data interpretation — but not yet accepted for publication (it is normal for scientific papers to go through a months-long process of review, rewrite and resubmission).
With all of last week's hoopla, Bennett blogged about some of the best comments he ran across regarding the dead salmon study. Here is one he considers spot on: "The recorded signal is changing due to noise. The point of the experiment is that if you look at enough signals, the noise in one will match the timing of your experimental stimulus, purely out of chance."
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In The Water Cooler, Imaginova's Editorial Director Robert Roy Britt looks at what people are talking about in the world of science and beyond. Find more in the archives and on Twitter.