They've "shown" when patients are in pain, how psychopaths' brains are different, and why some people are shy. And they've even been used to reconstruct watched videos in what was widely described as "mind reading."
Most of the time, these brain scans are functional magnetic resonance imaging (fMRI) studies, which measure the amount of oxygen in different parts of the brain. And, presumably, where there is more oxygen, there is more activity.
But it's pretty hard to keep a brain quiet. Even when you're inactive, there is still plenty of oxygen flow. Now researchers are studying the brain under these "normal" conditions -- when it's in resting state or performing simple tasks.
Two papers published last week showed that, when participants were just watching videos of peoples' faces or looking at patterns of numbers or letters, the entire brain lit up. You read that right: even when you're doing nothing in particular, the entire brain is active. And these studies were huge: in one, more than 1,300 peoples' brains were scanned, and in the other, three people each underwent the study 500 times each.
The findings suggest that most fMRI studies are presenting a "misleading picture of the brain," writes the blogger Neuroskeptic. If the whole brain is active most of the time, studies will only pick up the most extreme areas of activity, leaving smaller changes left unknown -- "[a] bit like how we only hear the shouts and screams from through our neighbor's walls, not their normal conversations, which aren't loud enough to reach our ears," he wrote. "The idea that only small parts of the brain are 'involved' in any particular task may be a statistical artefact."
But studying the brain's background noise won't just improve fMRI studies: some researchers want to use the information to diagnose brain disease.
The premise is fairly straight-forward: if brain connections are damaged in people with Alzheimer's disease, epilepsy or ADHD, maybe their "normal" brain static will differ as well. Roxanne Khamsi writes in Nature Medicine:
[I]ncreasingly, a group of neuroscientists believe that scientists focusing on task-based brain scans are missing the big picture. Over the last decade, momentum has swelled around the idea that examining resting-state fMRI, captured as people lie idle in the scanner, could reveal more intimate details about how brain regions communicate or fall out of sync as a result of disease. The approach, which might eventually be used as a diagnostic tool, has even caught the attention of some big-name drug developers.
Researchers are developing large databases, already with "resting brain" scans of more than 1,400 people, reports Khamsi.
The focus on "normal" brain states is compelling to me: before we start to pick apart behavior, shouldn't we first better understand the diversity among all human brains?
Brain Scanning - Just the Tip of the Iceberg? [Neuroskeptic]
Diagnosis by default [Nature Medicine]