The 18-inch-long Atlantic salmon lay perfectly still for its brain scan. Emotional pictures —a triumphant young girl just out of a somersault, a distressed waiter who had just dropped a plate — flashed in front of the fish as a scientist read the standard instruction script aloud. The hulking machine clunked and whirred, capturing minute changes in the salmon’s brain as it assessed the images. Millions of data points capturing the fluctuations in brain activity streamed into a powerful computer, which performed herculean number crunching, sorting out which data to pay attention to and which to ignore.
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, presumably reading the ebbs and flows of activity that underlie almost everything the brain does. Over the last two decades, fMRI has transformed neuroscience, enabling experiments that researchers once could only dream of. With fMRI, scientists claim to have found the brain regions responsible for musical ability, schadenfreude, Coca-Cola or Pepsi preference, fairness and even tennis skill, among many other highly publicized conclusions.
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 neuroscientist Nancy Kanwisher of MIT.