It isn’t breaking news, and it’s hardly science. Still, considering last month’s discussion of statistical rigor and the recent kerfuffle over a paper in a well-respected psychological journal purporting extra sensory perception, now is the perfect time to revisit the dead salmon study.
In 2005, a graduate student in the lab of Abigail Baird at Dartmouth College needed to test his fMRI protocols for an upcoming experiment. Having already tested a pumpkin and a cornish game hen, the obvious next step was to scan a whole salmon from the local supermarket. After his protocol was validated, he promptly forgot about the whole experience.
That is, until last year, when the group published the salmon results in the Journal of Serendipitous and Unexpected Results. Their purpose was to illustrate the need for rigorous statistical analysis of fMRI data. The experiment went as follows:
One mature Atlantic Salmon (Salmo salar) participated in the fMRI study. The salmon measured approximately 18 inches long, weighed 3.8 lbs, and was not alive at the time of scanning. It is not known if the salmon was male or female, but given the post-mortem state of the subject this was not thought to be a critical variable […] The task administered to the salmon involved completing an open-ended mentalizing task. The salmon was shown a series of photographs depicting human individuals in social situations with a speciﬁed emotional valence, either socially inclusive or socially exclusive. The salmon was asked to determine which emotion the individual in the photo must have been experiencing.
In this unabashedly silly experiment, they found that certain areas of the salmon’s brain show significant amounts of activation when asked to consider a person’s emotional state. Clearly something is wrong here—as the authors put it, “Either we have stumbled onto a rather amazing discovery in terms of post-mortem ichthyological cognition, or there is something a bit off with regard to our uncorrected statistical approach.”
Even though the paper is written with tongue in cheek, it serves as a reminder that improperly analyzed data can sometimes be extremely misleading. Next time you need to explain the danger of false positives, remember the dead salmon.
Craig Bennett (the graduate student) tells the story on his blog, Prefrontal
Bennett, C., Miller, M., & Wolford, G. (2009). Neural correlates of interspecies perspective taking in the post-mortem Atlantic Salmon: an argument for multiple comparisons correction. NeuroImage, 47 DOI: 10.1016/S1053-8119(09)71202-9