http://sciencenews.org/view/feature/...ling_the_brain

Trawling the brain
New findings raise questions about reliability of fMRI as gauge of neural activityBy Laura Sanders December 19th, 2009; Vol.176 #13 (p. 16)

18-inch-long Atlantic salmon lay perfectly still for its brain scan. Emotional pictures ...flashed in front of the fish as a scientist read the standard instruction script aloud. The hulking machine ... capturing minute changes in the salmon’s brain as it assessed the images...
By the end of the experiment, neuroscientist Craig Bennett and his colleagues at Dartmouth College could clearly discern in the scan of the salmon’s brain a beautiful, red-hot area of activity that lit up during emotional scenes.

An Atlantic salmon that responded to human emotions would have been an astounding discovery, guaranteeing publication in a top-tier journal and a life of scientific glory for the researchers. Except for one thing. The fish was dead.

The scanning technique used on the salmon — called functional magnetic resonance imaging — allows scientists to view the innards of a working brain..

But many scientists say that serious issues have been neglected during fMRI’s meteoric rise in popularity. Drawing conclusions from an fMRI experiment requires complex analyses relying on chains of assumptions. When subjected to critical scrutiny, inferences from such analyses and many of the assumptions don’t always hold true. Consequently, some experts allege, many results claimed from fMRI studies are simply dead wrong.

“It’s a dirty little secret in our field that many of the published findings are unlikely to replicate,” says neuro*scientist Nancy Kanwisher of MIT.

A reanalysis of the salmon’s post*mortem brain, using a statistical check to prevent random results from accidentally seeming significant, showed no red-hot regions at all, Bennett, now at the University of California, Santa Barbara, and colleagues report in a paper submitted to Human Brain Mapping. In other words, the whole brain was as cold as a dead fish...



Make no mistake: fMRI is a powerful tool allowing neuroscientists to elucidate some of the brain’s deepest secrets. It “provides you a different window into how mental processes work in the brain that we wouldn’t have had without it,” says Russell Poldrack of the University of Texas at Austin.

But like any powerful tool, fMRI must be used with caution. “All methods have shortcomings — conclusions they support and conclusions they don’t support,” Kanwisher says. “Neuroimaging is no exception.”