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Dead Salmon's "Brain Activity" Cautions fMRI Researchers
AthanasiusKircher sends in a Wired writeup on what should surely be a contender in the next Improbable Research competition: wiring a dead salmon into an fMRI machine and showing it pictures of humans designed to evoke various emotions. "When they got around to analyzing the voxel... data, the voxels representing the area where the salmon's tiny brain sat showed evidence of activity. In the fMRI scan, it looked like the dead salmon was actually thinking about the pictures it had been shown. ... The result is completely nuts — but that's actually exactly the point. [Neuroscientist Craig] Bennett... and his adviser, George Wolford, wrote up the work as a warning about the dangers of false positives in fMRI data. They wanted to call attention to ways the field could improve its statistical methods. ... Bennett notes: 'We could set our threshold [of significance] so high that we have no false positives, but we have no legitimate results.... We could also set it so low that we end up getting voxels in the fish's brain. It's the fine line that we walk.'" The research has been turned down by several publications, according to Wired, but a poster is available (PDF).
"That's precisely what this study is showing: even a dead fish has changing brain-blood oxygenation levels."
No, they're showing that the noise inherent in the scan can be taken for signal if you aren't careful with your stats. The dead fish is NOT exhibiting varying blood oxygenation levels.
Even the worst fMRI experiments that get published use a repetitive design, or equivalent. The simplest setup is to administer a stimulus or have the subject do something then stop, then do it again then stop, then do it again, etc. When you're done, you look for signals that vary in tandem with the stimulus.
A dead fish's brain does NOT have blood oxygenation levels that vary in that way. For the purposes of the experiment they're basically constant. However, if you look at enough different measurements, the noise superimposed on that static signal will correlate with the stimulus.
The fish is just for laughs. They could have easily done the same thing with a jar of agar.
Atlantic salmon is called Salmo salar in biology-speak. It is the model species of the entire order Salmoniformes. Salmon doesn't get any truer than that. Pacific species belong to the genus Oncorhynchus. They are true salmons too. "Trouts" belong to both Oncorhynchus and Salmo (and another 5 genera). Some of these trouts have anadromous forms (that is, go to the seas and return to the rivers to spawn), for instance, the rainbow trout (called steelhead in its anadromous form) is Oncorhynchus mykiss and the brown trout (sea trout) is Salmo trutta.